New upstream version 2.2.4.4

6 files changed, 6926 insertions, 0 deletions

diff --git a/opusfile/info.c b/opusfile/info.c
new file mode 100644
index 0000000..3a1a5bf
--- /dev/null
+++ b/opusfile/info.c
@@ -0,0 +1,771 @@
+/********************************************************************
+ *                                                                  *
+ * THIS FILE IS PART OF THE libopusfile SOFTWARE CODEC SOURCE CODE. *
+ * USE, DISTRIBUTION AND REPRODUCTION OF THIS LIBRARY SOURCE IS     *
+ * GOVERNED BY A BSD-STYLE SOURCE LICENSE INCLUDED WITH THIS SOURCE *
+ * IN 'COPYING'. PLEASE READ THESE TERMS BEFORE DISTRIBUTING.       *
+ *                                                                  *
+ * THE libopusfile SOURCE CODE IS (C) COPYRIGHT 2012                *
+ * by the Xiph.Org Foundation and contributors http://www.xiph.org/ *
+ *                                                                  *
+ ********************************************************************/
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "internal.h"
+#include <limits.h>
+#include <string.h>
+
+static unsigned op_parse_uint16le(const unsigned char *_data){
+  return _data[0]|_data[1]<<8;
+}
+
+static int op_parse_int16le(const unsigned char *_data){
+  int ret;
+  ret=_data[0]|_data[1]<<8;
+  return (ret^0x8000)-0x8000;
+}
+
+static opus_uint32 op_parse_uint32le(const unsigned char *_data){
+  return _data[0]|(opus_uint32)_data[1]<<8|
+   (opus_uint32)_data[2]<<16|(opus_uint32)_data[3]<<24;
+}
+
+static opus_uint32 op_parse_uint32be(const unsigned char *_data){
+  return _data[3]|(opus_uint32)_data[2]<<8|
+   (opus_uint32)_data[1]<<16|(opus_uint32)_data[0]<<24;
+}
+
+int opus_head_parse(OpusHead *_head,const unsigned char *_data,size_t _len){
+  OpusHead head;
+  if(_len<8)return OP_ENOTFORMAT;
+  if(memcmp(_data,"OpusHead",8)!=0)return OP_ENOTFORMAT;
+  if(_len<9)return OP_EBADHEADER;
+  head.version=_data[8];
+  if(head.version>15)return OP_EVERSION;
+  if(_len<19)return OP_EBADHEADER;
+  head.channel_count=_data[9];
+  head.pre_skip=op_parse_uint16le(_data+10);
+  head.input_sample_rate=op_parse_uint32le(_data+12);
+  head.output_gain=op_parse_int16le(_data+16);
+  head.mapping_family=_data[18];
+  if(head.mapping_family==0){
+    if(head.channel_count<1||head.channel_count>2)return OP_EBADHEADER;
+    if(head.version<=1&&_len>19)return OP_EBADHEADER;
+    head.stream_count=1;
+    head.coupled_count=head.channel_count-1;
+    if(_head!=NULL){
+      _head->mapping[0]=0;
+      _head->mapping[1]=1;
+    }
+  }
+  else if(head.mapping_family==1){
+    size_t size;
+    int    ci;
+    if(head.channel_count<1||head.channel_count>8)return OP_EBADHEADER;
+    size=21+head.channel_count;
+    if(_len<size||head.version<=1&&_len>size)return OP_EBADHEADER;
+    head.stream_count=_data[19];
+    if(head.stream_count<1)return OP_EBADHEADER;
+    head.coupled_count=_data[20];
+    if(head.coupled_count>head.stream_count)return OP_EBADHEADER;
+    for(ci=0;ci<head.channel_count;ci++){
+      if(_data[21+ci]>=head.stream_count+head.coupled_count
+       &&_data[21+ci]!=255){
+        return OP_EBADHEADER;
+      }
+    }
+    if(_head!=NULL)memcpy(_head->mapping,_data+21,head.channel_count);
+  }
+  /*General purpose players should not attempt to play back content with
+     channel mapping family 255.*/
+  else if(head.mapping_family==255)return OP_EIMPL;
+  /*No other channel mapping families are currently defined.*/
+  else return OP_EBADHEADER;
+  if(_head!=NULL)memcpy(_head,&head,head.mapping-(unsigned char *)&head);
+  return 0;
+}
+
+void opus_tags_init(OpusTags *_tags){
+  memset(_tags,0,sizeof(*_tags));
+}
+
+void opus_tags_clear(OpusTags *_tags){
+  int ncomments;
+  int ci;
+  ncomments=_tags->comments;
+  if(_tags->user_comments!=NULL)ncomments++;
+  for(ci=ncomments;ci-->0;)_ogg_free(_tags->user_comments[ci]);
+  _ogg_free(_tags->user_comments);
+  _ogg_free(_tags->comment_lengths);
+  _ogg_free(_tags->vendor);
+}
+
+/*Ensure there's room for up to _ncomments comments.*/
+static int op_tags_ensure_capacity(OpusTags *_tags,size_t _ncomments){
+  char   **user_comments;
+  int     *comment_lengths;
+  int      cur_ncomments;
+  size_t   size;
+  if(OP_UNLIKELY(_ncomments>=(size_t)INT_MAX))return OP_EFAULT;
+  size=sizeof(*_tags->comment_lengths)*(_ncomments+1);
+  if(size/sizeof(*_tags->comment_lengths)!=_ncomments+1)return OP_EFAULT;
+  cur_ncomments=_tags->comments;
+  /*We only support growing.
+    Trimming requires cleaning up the allocated strings in the old space, and
+     is best handled separately if it's ever needed.*/
+  OP_ASSERT(_ncomments>=(size_t)cur_ncomments);
+  comment_lengths=(int *)_ogg_realloc(_tags->comment_lengths,size);
+  if(OP_UNLIKELY(comment_lengths==NULL))return OP_EFAULT;
+  if(_tags->comment_lengths==NULL){
+    OP_ASSERT(cur_ncomments==0);
+    comment_lengths[cur_ncomments]=0;
+  }
+  comment_lengths[_ncomments]=comment_lengths[cur_ncomments];
+  _tags->comment_lengths=comment_lengths;
+  size=sizeof(*_tags->user_comments)*(_ncomments+1);
+  if(size/sizeof(*_tags->user_comments)!=_ncomments+1)return OP_EFAULT;
+  user_comments=(char **)_ogg_realloc(_tags->user_comments,size);
+  if(OP_UNLIKELY(user_comments==NULL))return OP_EFAULT;
+  if(_tags->user_comments==NULL){
+    OP_ASSERT(cur_ncomments==0);
+    user_comments[cur_ncomments]=NULL;
+  }
+  user_comments[_ncomments]=user_comments[cur_ncomments];
+  _tags->user_comments=user_comments;
+  return 0;
+}
+
+/*Duplicate a (possibly non-NUL terminated) string with a known length.*/
+static char *op_strdup_with_len(const char *_s,size_t _len){
+  size_t  size;
+  char   *ret;
+  size=sizeof(*ret)*(_len+1);
+  if(OP_UNLIKELY(size<_len))return NULL;
+  ret=(char *)_ogg_malloc(size);
+  if(OP_LIKELY(ret!=NULL)){
+    ret=(char *)memcpy(ret,_s,sizeof(*ret)*_len);
+    ret[_len]='\0';
+  }
+  return ret;
+}
+
+/*The actual implementation of opus_tags_parse().
+  Unlike the public API, this function requires _tags to already be
+   initialized, modifies its contents before success is guaranteed, and assumes
+   the caller will clear it on error.*/
+static int opus_tags_parse_impl(OpusTags *_tags,
+ const unsigned char *_data,size_t _len){
+  opus_uint32 count;
+  size_t      len;
+  int         ncomments;
+  int         ci;
+  len=_len;
+  if(len<8)return OP_ENOTFORMAT;
+  if(memcmp(_data,"OpusTags",8)!=0)return OP_ENOTFORMAT;
+  if(len<16)return OP_EBADHEADER;
+  _data+=8;
+  len-=8;
+  count=op_parse_uint32le(_data);
+  _data+=4;
+  len-=4;
+  if(count>len)return OP_EBADHEADER;
+  if(_tags!=NULL){
+    _tags->vendor=op_strdup_with_len((char *)_data,count);
+    if(_tags->vendor==NULL)return OP_EFAULT;
+  }
+  _data+=count;
+  len-=count;
+  if(len<4)return OP_EBADHEADER;
+  count=op_parse_uint32le(_data);
+  _data+=4;
+  len-=4;
+  /*Check to make sure there's minimally sufficient data left in the packet.*/
+  if(count>len>>2)return OP_EBADHEADER;
+  /*Check for overflow (the API limits this to an int).*/
+  if(count>(opus_uint32)INT_MAX-1)return OP_EFAULT;
+  if(_tags!=NULL){
+    int ret;
+    ret=op_tags_ensure_capacity(_tags,count);
+    if(ret<0)return ret;
+  }
+  ncomments=(int)count;
+  for(ci=0;ci<ncomments;ci++){
+    /*Check to make sure there's minimally sufficient data left in the packet.*/
+    if((size_t)(ncomments-ci)>len>>2)return OP_EBADHEADER;
+    count=op_parse_uint32le(_data);
+    _data+=4;
+    len-=4;
+    if(count>len)return OP_EBADHEADER;
+    /*Check for overflow (the API limits this to an int).*/
+    if(count>(opus_uint32)INT_MAX)return OP_EFAULT;
+    if(_tags!=NULL){
+      _tags->user_comments[ci]=op_strdup_with_len((char *)_data,count);
+      if(_tags->user_comments[ci]==NULL)return OP_EFAULT;
+      _tags->comment_lengths[ci]=(int)count;
+      _tags->comments=ci+1;
+      /*Needed by opus_tags_clear() if we fail before parsing the (optional)
+         binary metadata.*/
+      _tags->user_comments[ci+1]=NULL;
+    }
+    _data+=count;
+    len-=count;
+  }
+  if(len>0&&(_data[0]&1)){
+    if(len>(opus_uint32)INT_MAX)return OP_EFAULT;
+    if(_tags!=NULL){
+      _tags->user_comments[ncomments]=(char *)_ogg_malloc(len);
+      if(OP_UNLIKELY(_tags->user_comments[ncomments]==NULL))return OP_EFAULT;
+      memcpy(_tags->user_comments[ncomments],_data,len);
+      _tags->comment_lengths[ncomments]=(int)len;
+    }
+  }
+  return 0;
+}
+
+int opus_tags_parse(OpusTags *_tags,const unsigned char *_data,size_t _len){
+  if(_tags!=NULL){
+    OpusTags tags;
+    int      ret;
+    opus_tags_init(&tags);
+    ret=opus_tags_parse_impl(&tags,_data,_len);
+    if(ret<0)opus_tags_clear(&tags);
+    else *_tags=*&tags;
+    return ret;
+  }
+  else return opus_tags_parse_impl(NULL,_data,_len);
+}
+
+/*The actual implementation of opus_tags_copy().
+  Unlike the public API, this function requires _dst to already be
+   initialized, modifies its contents before success is guaranteed, and assumes
+   the caller will clear it on error.*/
+static int opus_tags_copy_impl(OpusTags *_dst,const OpusTags *_src){
+  char *vendor;
+  int   ncomments;
+  int   ret;
+  int   ci;
+  vendor=_src->vendor;
+  _dst->vendor=op_strdup_with_len(vendor,strlen(vendor));
+  if(OP_UNLIKELY(_dst->vendor==NULL))return OP_EFAULT;
+  ncomments=_src->comments;
+  ret=op_tags_ensure_capacity(_dst,ncomments);
+  if(OP_UNLIKELY(ret<0))return ret;
+  for(ci=0;ci<ncomments;ci++){
+    int len;
+    len=_src->comment_lengths[ci];
+    OP_ASSERT(len>=0);
+    _dst->user_comments[ci]=op_strdup_with_len(_src->user_comments[ci],len);
+    if(OP_UNLIKELY(_dst->user_comments[ci]==NULL))return OP_EFAULT;
+    _dst->comment_lengths[ci]=len;
+    _dst->comments=ci+1;
+  }
+  if(_src->comment_lengths!=NULL){
+    int len;
+    len=_src->comment_lengths[ncomments];
+    if(len>0){
+      _dst->user_comments[ncomments]=(char *)_ogg_malloc(len);
+      if(OP_UNLIKELY(_dst->user_comments[ncomments]==NULL))return OP_EFAULT;
+      memcpy(_dst->user_comments[ncomments],_src->user_comments[ncomments],len);
+      _dst->comment_lengths[ncomments]=len;
+    }
+  }
+  return 0;
+}
+
+int opus_tags_copy(OpusTags *_dst,const OpusTags *_src){
+  OpusTags dst;
+  int      ret;
+  opus_tags_init(&dst);
+  ret=opus_tags_copy_impl(&dst,_src);
+  if(OP_UNLIKELY(ret<0))opus_tags_clear(&dst);
+  else *_dst=*&dst;
+  return ret;
+}
+
+int opus_tags_add(OpusTags *_tags,const char *_tag,const char *_value){
+  char   *comment;
+  size_t  tag_len;
+  size_t  value_len;
+  int     ncomments;
+  int     ret;
+  ncomments=_tags->comments;
+  ret=op_tags_ensure_capacity(_tags,ncomments+1);
+  if(OP_UNLIKELY(ret<0))return ret;
+  tag_len=strlen(_tag);
+  value_len=strlen(_value);
+  /*+2 for '=' and '\0'.*/
+  if(tag_len+value_len<tag_len)return OP_EFAULT;
+  if(tag_len+value_len>(size_t)INT_MAX-2)return OP_EFAULT;
+  comment=(char *)_ogg_malloc(sizeof(*comment)*(tag_len+value_len+2));
+  if(OP_UNLIKELY(comment==NULL))return OP_EFAULT;
+  memcpy(comment,_tag,sizeof(*comment)*tag_len);
+  comment[tag_len]='=';
+  memcpy(comment+tag_len+1,_value,sizeof(*comment)*(value_len+1));
+  _tags->user_comments[ncomments]=comment;
+  _tags->comment_lengths[ncomments]=(int)(tag_len+value_len+1);
+  _tags->comments=ncomments+1;
+  return 0;
+}
+
+int opus_tags_add_comment(OpusTags *_tags,const char *_comment){
+  char *comment;
+  int   comment_len;
+  int   ncomments;
+  int   ret;
+  ncomments=_tags->comments;
+  ret=op_tags_ensure_capacity(_tags,ncomments+1);
+  if(OP_UNLIKELY(ret<0))return ret;
+  comment_len=(int)strlen(_comment);
+  comment=op_strdup_with_len(_comment,comment_len);
+  if(OP_UNLIKELY(comment==NULL))return OP_EFAULT;
+  _tags->user_comments[ncomments]=comment;
+  _tags->comment_lengths[ncomments]=comment_len;
+  _tags->comments=ncomments+1;
+  return 0;
+}
+
+int opus_tags_set_binary_suffix(OpusTags *_tags,
+ const unsigned char *_data,int _len){
+  unsigned char *binary_suffix_data;
+  int            ncomments;
+  int            ret;
+  if(_len<0||_len>0&&(_data==NULL||!(_data[0]&1)))return OP_EINVAL;
+  ncomments=_tags->comments;
+  ret=op_tags_ensure_capacity(_tags,ncomments);
+  if(OP_UNLIKELY(ret<0))return ret;
+  binary_suffix_data=
+   (unsigned char *)_ogg_realloc(_tags->user_comments[ncomments],_len);
+  if(OP_UNLIKELY(binary_suffix_data==NULL))return OP_EFAULT;
+  memcpy(binary_suffix_data,_data,_len);
+  _tags->user_comments[ncomments]=(char *)binary_suffix_data;
+  _tags->comment_lengths[ncomments]=_len;
+  return 0;
+}
+
+int opus_tagcompare(const char *_tag_name,const char *_comment){
+  size_t tag_len;
+  tag_len=strlen(_tag_name);
+  if(OP_UNLIKELY(tag_len>(size_t)INT_MAX))return -1;
+  return opus_tagncompare(_tag_name,(int)tag_len,_comment);
+}
+
+int opus_tagncompare(const char *_tag_name,int _tag_len,const char *_comment){
+  int ret;
+  OP_ASSERT(_tag_len>=0);
+  ret=op_strncasecmp(_tag_name,_comment,_tag_len);
+  return ret?ret:'='-_comment[_tag_len];
+}
+
+const char *opus_tags_query(const OpusTags *_tags,const char *_tag,int _count){
+  char   **user_comments;
+  size_t   tag_len;
+  int      found;
+  int      ncomments;
+  int      ci;
+  tag_len=strlen(_tag);
+  if(OP_UNLIKELY(tag_len>(size_t)INT_MAX))return NULL;
+  ncomments=_tags->comments;
+  user_comments=_tags->user_comments;
+  found=0;
+  for(ci=0;ci<ncomments;ci++){
+    if(!opus_tagncompare(_tag,(int)tag_len,user_comments[ci])){
+      /*We return a pointer to the data, not a copy.*/
+      if(_count==found++)return user_comments[ci]+tag_len+1;
+    }
+  }
+  /*Didn't find anything.*/
+  return NULL;
+}
+
+int opus_tags_query_count(const OpusTags *_tags,const char *_tag){
+  char   **user_comments;
+  size_t   tag_len;
+  int      found;
+  int      ncomments;
+  int      ci;
+  tag_len=strlen(_tag);
+  if(OP_UNLIKELY(tag_len>(size_t)INT_MAX))return 0;
+  ncomments=_tags->comments;
+  user_comments=_tags->user_comments;
+  found=0;
+  for(ci=0;ci<ncomments;ci++){
+    if(!opus_tagncompare(_tag,(int)tag_len,user_comments[ci]))found++;
+  }
+  return found;
+}
+
+const unsigned char *opus_tags_get_binary_suffix(const OpusTags *_tags,
+ int *_len){
+  int ncomments;
+  int len;
+  ncomments=_tags->comments;
+  len=_tags->comment_lengths==NULL?0:_tags->comment_lengths[ncomments];
+  *_len=len;
+  OP_ASSERT(len==0||_tags->user_comments!=NULL);
+  return len>0?(const unsigned char *)_tags->user_comments[ncomments]:NULL;
+}
+
+static int opus_tags_get_gain(const OpusTags *_tags,int *_gain_q8,
+ const char *_tag_name,size_t _tag_len){
+  char **comments;
+  int    ncomments;
+  int    ci;
+  comments=_tags->user_comments;
+  ncomments=_tags->comments;
+  /*Look for the first valid tag with the name _tag_name and use that.*/
+  for(ci=0;ci<ncomments;ci++){
+    OP_ASSERT(_tag_len<=(size_t)INT_MAX);
+    if(opus_tagncompare(_tag_name,(int)_tag_len,comments[ci])==0){
+      char       *p;
+      opus_int32  gain_q8;
+      int         negative;
+      p=comments[ci]+_tag_len+1;
+      negative=0;
+      if(*p=='-'){
+        negative=-1;
+        p++;
+      }
+      else if(*p=='+')p++;
+      gain_q8=0;
+      while(*p>='0'&&*p<='9'){
+        gain_q8=10*gain_q8+*p-'0';
+        if(gain_q8>32767-negative)break;
+        p++;
+      }
+      /*This didn't look like a signed 16-bit decimal integer.
+        Not a valid gain tag.*/
+      if(*p!='\0')continue;
+      *_gain_q8=(int)(gain_q8+negative^negative);
+      return 0;
+    }
+  }
+  return OP_FALSE;
+}
+
+int opus_tags_get_album_gain(const OpusTags *_tags,int *_gain_q8){
+  return opus_tags_get_gain(_tags,_gain_q8,"R128_ALBUM_GAIN",15);
+}
+
+int opus_tags_get_track_gain(const OpusTags *_tags,int *_gain_q8){
+  return opus_tags_get_gain(_tags,_gain_q8,"R128_TRACK_GAIN",15);
+}
+
+static int op_is_jpeg(const unsigned char *_buf,size_t _buf_sz){
+  return _buf_sz>=3&&memcmp(_buf,"\xFF\xD8\xFF",3)==0;
+}
+
+/*Tries to extract the width, height, bits per pixel, and palette size of a
+   JPEG.
+  On failure, simply leaves its outputs unmodified.*/
+static void op_extract_jpeg_params(const unsigned char *_buf,size_t _buf_sz,
+ opus_uint32 *_width,opus_uint32 *_height,
+ opus_uint32 *_depth,opus_uint32 *_colors,int *_has_palette){
+  if(op_is_jpeg(_buf,_buf_sz)){
+    size_t offs;
+    offs=2;
+    for(;;){
+      size_t segment_len;
+      int    marker;
+      while(offs<_buf_sz&&_buf[offs]!=0xFF)offs++;
+      while(offs<_buf_sz&&_buf[offs]==0xFF)offs++;
+      marker=_buf[offs];
+      offs++;
+      /*If we hit EOI* (end of image), or another SOI* (start of image),
+         or SOS (start of scan), then stop now.*/
+      if(offs>=_buf_sz||(marker>=0xD8&&marker<=0xDA))break;
+      /*RST* (restart markers): skip (no segment length).*/
+      else if(marker>=0xD0&&marker<=0xD7)continue;
+      /*Read the length of the marker segment.*/
+      if(_buf_sz-offs<2)break;
+      segment_len=_buf[offs]<<8|_buf[offs+1];
+      if(segment_len<2||_buf_sz-offs<segment_len)break;
+      if(marker==0xC0||(marker>0xC0&&marker<0xD0&&(marker&3)!=0)){
+        /*Found a SOFn (start of frame) marker segment:*/
+        if(segment_len>=8){
+          *_height=_buf[offs+3]<<8|_buf[offs+4];
+          *_width=_buf[offs+5]<<8|_buf[offs+6];
+          *_depth=_buf[offs+2]*_buf[offs+7];
+          *_colors=0;
+          *_has_palette=0;
+        }
+        break;
+      }
+      /*Other markers: skip the whole marker segment.*/
+      offs+=segment_len;
+    }
+  }
+}
+
+static int op_is_png(const unsigned char *_buf,size_t _buf_sz){
+  return _buf_sz>=8&&memcmp(_buf,"\x89PNG\x0D\x0A\x1A\x0A",8)==0;
+}
+
+/*Tries to extract the width, height, bits per pixel, and palette size of a
+   PNG.
+  On failure, simply leaves its outputs unmodified.*/
+static void op_extract_png_params(const unsigned char *_buf,size_t _buf_sz,
+ opus_uint32 *_width,opus_uint32 *_height,
+ opus_uint32 *_depth,opus_uint32 *_colors,int *_has_palette){
+  if(op_is_png(_buf,_buf_sz)){
+    size_t offs;
+    offs=8;
+    while(_buf_sz-offs>=12){
+      ogg_uint32_t chunk_len;
+      chunk_len=op_parse_uint32be(_buf+offs);
+      if(chunk_len>_buf_sz-(offs+12))break;
+      else if(chunk_len==13&&memcmp(_buf+offs+4,"IHDR",4)==0){
+        int color_type;
+        *_width=op_parse_uint32be(_buf+offs+8);
+        *_height=op_parse_uint32be(_buf+offs+12);
+        color_type=_buf[offs+17];
+        if(color_type==3){
+          *_depth=24;
+          *_has_palette=1;
+        }
+        else{
+          int sample_depth;
+          sample_depth=_buf[offs+16];
+          if(color_type==0)*_depth=sample_depth;
+          else if(color_type==2)*_depth=sample_depth*3;
+          else if(color_type==4)*_depth=sample_depth*2;
+          else if(color_type==6)*_depth=sample_depth*4;
+          *_colors=0;
+          *_has_palette=0;
+          break;
+        }
+      }
+      else if(*_has_palette>0&&memcmp(_buf+offs+4,"PLTE",4)==0){
+        *_colors=chunk_len/3;
+        break;
+      }
+      offs+=12+chunk_len;
+    }
+  }
+}
+
+static int op_is_gif(const unsigned char *_buf,size_t _buf_sz){
+  return _buf_sz>=6&&(memcmp(_buf,"GIF87a",6)==0||memcmp(_buf,"GIF89a",6)==0);
+}
+
+/*Tries to extract the width, height, bits per pixel, and palette size of a
+   GIF.
+  On failure, simply leaves its outputs unmodified.*/
+static void op_extract_gif_params(const unsigned char *_buf,size_t _buf_sz,
+ opus_uint32 *_width,opus_uint32 *_height,
+ opus_uint32 *_depth,opus_uint32 *_colors,int *_has_palette){
+  if(op_is_gif(_buf,_buf_sz)&&_buf_sz>=14){
+    *_width=_buf[6]|_buf[7]<<8;
+    *_height=_buf[8]|_buf[9]<<8;
+    /*libFLAC hard-codes the depth to 24.*/
+    *_depth=24;
+    *_colors=1<<((_buf[10]&7)+1);
+    *_has_palette=1;
+  }
+}
+
+/*The actual implementation of opus_picture_tag_parse().
+  Unlike the public API, this function requires _pic to already be
+   initialized, modifies its contents before success is guaranteed, and assumes
+   the caller will clear it on error.*/
+static int opus_picture_tag_parse_impl(OpusPictureTag *_pic,const char *_tag,
+ unsigned char *_buf,size_t _buf_sz,size_t _base64_sz){
+  opus_int32   picture_type;
+  opus_uint32  mime_type_length;
+  char        *mime_type;
+  opus_uint32  description_length;
+  char        *description;
+  opus_uint32  width;
+  opus_uint32  height;
+  opus_uint32  depth;
+  opus_uint32  colors;
+  opus_uint32  data_length;
+  opus_uint32  file_width;
+  opus_uint32  file_height;
+  opus_uint32  file_depth;
+  opus_uint32  file_colors;
+  int          format;
+  int          has_palette;
+  int          colors_set;
+  size_t       i;
+  /*Decode the BASE64 data.*/
+  for(i=0;i<_base64_sz;i++){
+    opus_uint32 value;
+    int         j;
+    value=0;
+    for(j=0;j<4;j++){
+      unsigned c;
+      unsigned d;
+      c=(unsigned char)_tag[4*i+j];
+      if(c=='+')d=62;
+      else if(c=='/')d=63;
+      else if(c>='0'&&c<='9')d=52+c-'0';
+      else if(c>='a'&&c<='z')d=26+c-'a';
+      else if(c>='A'&&c<='Z')d=c-'A';
+      else if(c=='='&&3*i+j>_buf_sz)d=0;
+      else return OP_ENOTFORMAT;
+      value=value<<6|d;
+    }
+    _buf[3*i]=(unsigned char)(value>>16);
+    if(3*i+1<_buf_sz){
+      _buf[3*i+1]=(unsigned char)(value>>8);
+      if(3*i+2<_buf_sz)_buf[3*i+2]=(unsigned char)value;
+    }
+  }
+  i=0;
+  picture_type=op_parse_uint32be(_buf+i);
+  i+=4;
+  /*Extract the MIME type.*/
+  mime_type_length=op_parse_uint32be(_buf+i);
+  i+=4;
+  if(mime_type_length>_buf_sz-32)return OP_ENOTFORMAT;
+  mime_type=(char *)_ogg_malloc(sizeof(*_pic->mime_type)*(mime_type_length+1));
+  if(mime_type==NULL)return OP_EFAULT;
+  memcpy(mime_type,_buf+i,sizeof(*mime_type)*mime_type_length);
+  mime_type[mime_type_length]='\0';
+  _pic->mime_type=mime_type;
+  i+=mime_type_length;
+  /*Extract the description string.*/
+  description_length=op_parse_uint32be(_buf+i);
+  i+=4;
+  if(description_length>_buf_sz-mime_type_length-32)return OP_ENOTFORMAT;
+  description=
+   (char *)_ogg_malloc(sizeof(*_pic->mime_type)*(description_length+1));
+  if(description==NULL)return OP_EFAULT;
+  memcpy(description,_buf+i,sizeof(*description)*description_length);
+  description[description_length]='\0';
+  _pic->description=description;
+  i+=description_length;
+  /*Extract the remaining fields.*/
+  width=op_parse_uint32be(_buf+i);
+  i+=4;
+  height=op_parse_uint32be(_buf+i);
+  i+=4;
+  depth=op_parse_uint32be(_buf+i);
+  i+=4;
+  colors=op_parse_uint32be(_buf+i);
+  i+=4;
+  /*If one of these is set, they all must be, but colors==0 is a valid value.*/
+  colors_set=width!=0||height!=0||depth!=0||colors!=0;
+  if((width==0||height==0||depth==0)&&colors_set)return OP_ENOTFORMAT;
+  data_length=op_parse_uint32be(_buf+i);
+  i+=4;
+  if(data_length>_buf_sz-i)return OP_ENOTFORMAT;
+  /*Trim extraneous data so we don't copy it below.*/
+  _buf_sz=i+data_length;
+  /*Attempt to determine the image format.*/
+  format=OP_PIC_FORMAT_UNKNOWN;
+  if(mime_type_length==3&&strcmp(mime_type,"-->")==0){
+    format=OP_PIC_FORMAT_URL;
+    /*Picture type 1 must be a 32x32 PNG.*/
+    if(picture_type==1&&(width!=0||height!=0)&&(width!=32||height!=32)){
+      return OP_ENOTFORMAT;
+    }
+    /*Append a terminating NUL for the convenience of our callers.*/
+    _buf[_buf_sz++]='\0';
+  }
+  else{
+    if(mime_type_length==10
+     &&op_strncasecmp(mime_type,"image/jpeg",mime_type_length)==0){
+      if(op_is_jpeg(_buf+i,data_length))format=OP_PIC_FORMAT_JPEG;
+    }
+    else if(mime_type_length==9
+     &&op_strncasecmp(mime_type,"image/png",mime_type_length)==0){
+      if(op_is_png(_buf+i,data_length))format=OP_PIC_FORMAT_PNG;
+    }
+    else if(mime_type_length==9
+     &&op_strncasecmp(mime_type,"image/gif",mime_type_length)==0){
+      if(op_is_gif(_buf+i,data_length))format=OP_PIC_FORMAT_GIF;
+    }
+    else if(mime_type_length==0||(mime_type_length==6
+     &&op_strncasecmp(mime_type,"image/",mime_type_length)==0)){
+      if(op_is_jpeg(_buf+i,data_length))format=OP_PIC_FORMAT_JPEG;
+      else if(op_is_png(_buf+i,data_length))format=OP_PIC_FORMAT_PNG;
+      else if(op_is_gif(_buf+i,data_length))format=OP_PIC_FORMAT_GIF;
+    }
+    file_width=file_height=file_depth=file_colors=0;
+    has_palette=-1;
+    switch(format){
+      case OP_PIC_FORMAT_JPEG:{
+        op_extract_jpeg_params(_buf+i,data_length,
+         &file_width,&file_height,&file_depth,&file_colors,&has_palette);
+      }break;
+      case OP_PIC_FORMAT_PNG:{
+        op_extract_png_params(_buf+i,data_length,
+         &file_width,&file_height,&file_depth,&file_colors,&has_palette);
+      }break;
+      case OP_PIC_FORMAT_GIF:{
+        op_extract_gif_params(_buf+i,data_length,
+         &file_width,&file_height,&file_depth,&file_colors,&has_palette);
+      }break;
+    }
+    if(has_palette>=0){
+      /*If we successfully extracted these parameters from the image, override
+         any declared values.*/
+      width=file_width;
+      height=file_height;
+      depth=file_depth;
+      colors=file_colors;
+    }
+    /*Picture type 1 must be a 32x32 PNG.*/
+    if(picture_type==1&&(format!=OP_PIC_FORMAT_PNG||width!=32||height!=32)){
+      return OP_ENOTFORMAT;
+    }
+  }
+  /*Adjust _buf_sz instead of using data_length to capture the terminating NUL
+     for URLs.*/
+  _buf_sz-=i;
+  memmove(_buf,_buf+i,sizeof(*_buf)*_buf_sz);
+  _buf=(unsigned char *)_ogg_realloc(_buf,_buf_sz);
+  if(_buf_sz>0&&_buf==NULL)return OP_EFAULT;
+  _pic->type=picture_type;
+  _pic->width=width;
+  _pic->height=height;
+  _pic->depth=depth;
+  _pic->colors=colors;
+  _pic->data_length=data_length;
+  _pic->data=_buf;
+  _pic->format=format;
+  return 0;
+}
+
+int opus_picture_tag_parse(OpusPictureTag *_pic,const char *_tag){
+  OpusPictureTag  pic;
+  unsigned char  *buf;
+  size_t          base64_sz;
+  size_t          buf_sz;
+  size_t          tag_length;
+  int             ret;
+  if(opus_tagncompare("METADATA_BLOCK_PICTURE",22,_tag)==0)_tag+=23;
+  /*Figure out how much BASE64-encoded data we have.*/
+  tag_length=strlen(_tag);
+  if(tag_length&3)return OP_ENOTFORMAT;
+  base64_sz=tag_length>>2;
+  buf_sz=3*base64_sz;
+  if(buf_sz<32)return OP_ENOTFORMAT;
+  if(_tag[tag_length-1]=='=')buf_sz--;
+  if(_tag[tag_length-2]=='=')buf_sz--;
+  if(buf_sz<32)return OP_ENOTFORMAT;
+  /*Allocate an extra byte to allow appending a terminating NUL to URL data.*/
+  buf=(unsigned char *)_ogg_malloc(sizeof(*buf)*(buf_sz+1));
+  if(buf==NULL)return OP_EFAULT;
+  opus_picture_tag_init(&pic);
+  ret=opus_picture_tag_parse_impl(&pic,_tag,buf,buf_sz,base64_sz);
+  if(ret<0){
+    opus_picture_tag_clear(&pic);
+    _ogg_free(buf);
+  }
+  else *_pic=*&pic;
+  return ret;
+}
+
+void opus_picture_tag_init(OpusPictureTag *_pic){
+  memset(_pic,0,sizeof(*_pic));
+}
+
+void opus_picture_tag_clear(OpusPictureTag *_pic){
+  _ogg_free(_pic->description);
+  _ogg_free(_pic->mime_type);
+  _ogg_free(_pic->data);
+}
diff --git a/opusfile/internal.c b/opusfile/internal.c
new file mode 100644
index 0000000..bd14cf6
--- /dev/null
+++ b/opusfile/internal.c
@@ -0,0 +1,42 @@
+/********************************************************************
+ *                                                                  *
+ * THIS FILE IS PART OF THE libopusfile SOFTWARE CODEC SOURCE CODE. *
+ * USE, DISTRIBUTION AND REPRODUCTION OF THIS LIBRARY SOURCE IS     *
+ * GOVERNED BY A BSD-STYLE SOURCE LICENSE INCLUDED WITH THIS SOURCE *
+ * IN 'COPYING'. PLEASE READ THESE TERMS BEFORE DISTRIBUTING.       *
+ *                                                                  *
+ * THE libopusfile SOURCE CODE IS (C) COPYRIGHT 2012                *
+ * by the Xiph.Org Foundation and contributors http://www.xiph.org/ *
+ *                                                                  *
+ ********************************************************************/
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "internal.h"
+
+#if defined(OP_ENABLE_ASSERTIONS)
+void op_fatal_impl(const char *_str,const char *_file,int _line){
+  fprintf(stderr,"Fatal (internal) error in %s, line %i: %s\n",
+   _file,_line,_str);
+  abort();
+}
+#endif
+
+/*A version of strncasecmp() that is guaranteed to only ignore the case of
+   ASCII characters.*/
+int op_strncasecmp(const char *_a,const char *_b,int _n){
+  int i;
+  for(i=0;i<_n;i++){
+    int a;
+    int b;
+    int d;
+    a=_a[i];
+    b=_b[i];
+    if(a>='a'&&a<='z')a-='a'-'A';
+    if(b>='a'&&b<='z')b-='a'-'A';
+    d=a-b;
+    if(d)return d;
+  }
+  return 0;
+}
\ No newline at end of file
diff --git a/opusfile/internal.h b/opusfile/internal.h
new file mode 100644
index 0000000..bb77fe1
--- /dev/null
+++ b/opusfile/internal.h
@@ -0,0 +1,259 @@
+/********************************************************************
+ *                                                                  *
+ * THIS FILE IS PART OF THE libopusfile SOFTWARE CODEC SOURCE CODE. *
+ * USE, DISTRIBUTION AND REPRODUCTION OF THIS LIBRARY SOURCE IS     *
+ * GOVERNED BY A BSD-STYLE SOURCE LICENSE INCLUDED WITH THIS SOURCE *
+ * IN 'COPYING'. PLEASE READ THESE TERMS BEFORE DISTRIBUTING.       *
+ *                                                                  *
+ * THE libopusfile SOURCE CODE IS (C) COPYRIGHT 2012                *
+ * by the Xiph.Org Foundation and contributors http://www.xiph.org/ *
+ *                                                                  *
+ ********************************************************************/
+#if !defined(_opusfile_internal_h)
+# define _opusfile_internal_h (1)
+
+# if !defined(_REENTRANT)
+#  define _REENTRANT
+# endif
+# if !defined(_GNU_SOURCE)
+#  define _GNU_SOURCE
+# endif
+# if !defined(_LARGEFILE_SOURCE)
+#  define _LARGEFILE_SOURCE
+# endif
+# if !defined(_LARGEFILE64_SOURCE)
+#  define _LARGEFILE64_SOURCE
+# endif
+# if !defined(_FILE_OFFSET_BITS)
+#  define _FILE_OFFSET_BITS 64
+# endif
+
+# include <stdlib.h>
+# include "opusfile.h"
+
+typedef struct OggOpusLink OggOpusLink;
+
+# if defined(OP_FIXED_POINT)
+
+typedef opus_int16 op_sample;
+
+# else
+
+typedef float      op_sample;
+
+/*We're using this define to test for libopus 1.1 or later until libopus
+   provides a better mechanism.*/
+#  if defined(OPUS_GET_EXPERT_FRAME_DURATION_REQUEST)
+/*Enable soft clipping prevention in 16-bit decodes.*/
+#   define OP_SOFT_CLIP (1)
+#  endif
+
+# endif
+
+# if OP_GNUC_PREREQ(4,2)
+/*Disable excessive warnings about the order of operations.*/
+#  pragma GCC diagnostic ignored "-Wparentheses"
+# elif defined(_MSC_VER)
+/*Disable excessive warnings about the order of operations.*/
+#  pragma warning(disable:4554)
+/*Disable warnings about "deprecated" POSIX functions.*/
+#  pragma warning(disable:4996)
+# endif
+
+# if OP_GNUC_PREREQ(3,0)
+/*Another alternative is
+    (__builtin_constant_p(_x)?!!(_x):__builtin_expect(!!(_x),1))
+   but that evaluates _x multiple times, which may be bad.*/
+#  define OP_LIKELY(_x) (__builtin_expect(!!(_x),1))
+#  define OP_UNLIKELY(_x) (__builtin_expect(!!(_x),0))
+# else
+#  define OP_LIKELY(_x)   (!!(_x))
+#  define OP_UNLIKELY(_x) (!!(_x))
+# endif
+
+# if defined(OP_ENABLE_ASSERTIONS)
+#  if OP_GNUC_PREREQ(2,5)||__SUNPRO_C>=0x590
+__attribute__((noreturn))
+#  endif
+void op_fatal_impl(const char *_str,const char *_file,int _line);
+
+#  define OP_FATAL(_str) (op_fatal_impl(_str,__FILE__,__LINE__))
+
+#  define OP_ASSERT(_cond) \
+  do{ \
+    if(OP_UNLIKELY(!(_cond)))OP_FATAL("assertion failed: " #_cond); \
+  } \
+  while(0)
+#  define OP_ALWAYS_TRUE(_cond) OP_ASSERT(_cond)
+
+# else
+#  define OP_FATAL(_str) abort()
+#  define OP_ASSERT(_cond)
+#  define OP_ALWAYS_TRUE(_cond) ((void)(_cond))
+# endif
+
+# define OP_INT64_MAX (2*(((ogg_int64_t)1<<62)-1)|1)
+# define OP_INT64_MIN (-OP_INT64_MAX-1)
+# define OP_INT32_MAX (2*(((ogg_int32_t)1<<30)-1)|1)
+# define OP_INT32_MIN (-OP_INT32_MAX-1)
+
+# define OP_MIN(_a,_b)        ((_a)<(_b)?(_a):(_b))
+# define OP_MAX(_a,_b)        ((_a)>(_b)?(_a):(_b))
+# define OP_CLAMP(_lo,_x,_hi) (OP_MAX(_lo,OP_MIN(_x,_hi)))
+
+/*Advance a file offset by the given amount, clamping against OP_INT64_MAX.
+  This is used to advance a known offset by things like OP_CHUNK_SIZE or
+   OP_PAGE_SIZE_MAX, while making sure to avoid signed overflow.
+  It assumes that both _offset and _amount are non-negative.*/
+#define OP_ADV_OFFSET(_offset,_amount) \
+ (OP_MIN(_offset,OP_INT64_MAX-(_amount))+(_amount))
+
+/*The maximum channel count for any mapping we'll actually decode.*/
+# define OP_NCHANNELS_MAX (8)
+
+/*Initial state.*/
+# define  OP_NOTOPEN   (0)
+/*We've found the first Opus stream in the first link.*/
+# define  OP_PARTOPEN  (1)
+# define  OP_OPENED    (2)
+/*We've found the first Opus stream in the current link.*/
+# define  OP_STREAMSET (3)
+/*We've initialized the decoder for the chosen Opus stream in the current
+   link.*/
+# define  OP_INITSET   (4)
+
+/*Information cached for a single link in a chained Ogg Opus file.
+  We choose the first Opus stream encountered in each link to play back (and
+   require at least one).*/
+struct OggOpusLink{
+  /*The byte offset of the first header page in this link.*/
+  opus_int64   offset;
+  /*The byte offset of the first data page from the chosen Opus stream in this
+     link (after the headers).*/
+  opus_int64   data_offset;
+  /*The byte offset of the last page from the chosen Opus stream in this link.
+    This is used when seeking to ensure we find a page before the last one, so
+     that end-trimming calculations work properly.
+    This is only valid for seekable sources.*/
+  opus_int64   end_offset;
+  /*The total duration of all prior links.
+    This is always zero for non-seekable sources.*/
+  ogg_int64_t  pcm_file_offset;
+  /*The granule position of the last sample.
+    This is only valid for seekable sources.*/
+  ogg_int64_t  pcm_end;
+  /*The granule position before the first sample.*/
+  ogg_int64_t  pcm_start;
+  /*The serial number.*/
+  ogg_uint32_t serialno;
+  /*The contents of the info header.*/
+  OpusHead     head;
+  /*The contents of the comment header.*/
+  OpusTags     tags;
+};
+
+struct OggOpusFile{
+  /*The callbacks used to access the stream.*/
+  OpusFileCallbacks  callbacks;
+  /*A FILE *, memory buffer, etc.*/
+  void              *stream;
+  /*Whether or not we can seek with this stream.*/
+  int                seekable;
+  /*The number of links in this chained Ogg Opus file.*/
+  int                nlinks;
+  /*The cached information from each link in a chained Ogg Opus file.
+    If stream isn't seekable (e.g., it's a pipe), only the current link
+     appears.*/
+  OggOpusLink       *links;
+  /*The number of serial numbers from a single link.*/
+  int                nserialnos;
+  /*The capacity of the list of serial numbers from a single link.*/
+  int                cserialnos;
+  /*Storage for the list of serial numbers from a single link.
+    This is a scratch buffer used when scanning the BOS pages at the start of
+     each link.*/
+  ogg_uint32_t      *serialnos;
+  /*This is the current offset of the data processed by the ogg_sync_state.
+    After a seek, this should be set to the target offset so that we can track
+     the byte offsets of subsequent pages.
+    After a call to op_get_next_page(), this will point to the first byte after
+     that page.*/
+  opus_int64         offset;
+  /*The total size of this stream, or -1 if it's unseekable.*/
+  opus_int64         end;
+  /*Used to locate pages in the stream.*/
+  ogg_sync_state     oy;
+  /*One of OP_NOTOPEN, OP_PARTOPEN, OP_OPENED, OP_STREAMSET, OP_INITSET.*/
+  int                ready_state;
+  /*The current link being played back.*/
+  int                cur_link;
+  /*The number of decoded samples to discard from the start of decoding.*/
+  opus_int32         cur_discard_count;
+  /*The granule position of the previous packet (current packet start time).*/
+  ogg_int64_t        prev_packet_gp;
+  /*The stream offset of the most recent page with completed packets, or -1.
+    This is only needed to recover continued packet data in the seeking logic,
+     when we use the current position as one of our bounds, only to later
+     discover it was the correct starting point.*/
+  opus_int64         prev_page_offset;
+  /*The number of bytes read since the last bitrate query, including framing.*/
+  opus_int64         bytes_tracked;
+  /*The number of samples decoded since the last bitrate query.*/
+  ogg_int64_t        samples_tracked;
+  /*Takes physical pages and welds them into a logical stream of packets.*/
+  ogg_stream_state   os;
+  /*Re-timestamped packets from a single page.
+    Buffering these relies on the undocumented libogg behavior that ogg_packet
+     pointers remain valid until the next page is submitted to the
+     ogg_stream_state they came from.*/
+  ogg_packet         op[255];
+  /*The index of the next packet to return.*/
+  int                op_pos;
+  /*The total number of packets available.*/
+  int                op_count;
+  /*Central working state for the packet-to-PCM decoder.*/
+  OpusMSDecoder     *od;
+  /*The application-provided packet decode callback.*/
+  op_decode_cb_func  decode_cb;
+  /*The application-provided packet decode callback context.*/
+  void              *decode_cb_ctx;
+  /*The stream count used to initialize the decoder.*/
+  int                od_stream_count;
+  /*The coupled stream count used to initialize the decoder.*/
+  int                od_coupled_count;
+  /*The channel count used to initialize the decoder.*/
+  int                od_channel_count;
+  /*The channel mapping used to initialize the decoder.*/
+  unsigned char      od_mapping[OP_NCHANNELS_MAX];
+  /*The buffered data for one decoded packet.*/
+  op_sample         *od_buffer;
+  /*The current position in the decoded buffer.*/
+  int                od_buffer_pos;
+  /*The number of valid samples in the decoded buffer.*/
+  int                od_buffer_size;
+  /*The type of gain offset to apply.
+    One of OP_HEADER_GAIN, OP_ALBUM_GAIN, OP_TRACK_GAIN, or OP_ABSOLUTE_GAIN.*/
+  int                gain_type;
+  /*The offset to apply to the gain.*/
+  opus_int32         gain_offset_q8;
+  /*Internal state for soft clipping and dithering float->short output.*/
+#if !defined(OP_FIXED_POINT)
+# if defined(OP_SOFT_CLIP)
+  float              clip_state[OP_NCHANNELS_MAX];
+# endif
+  float              dither_a[OP_NCHANNELS_MAX*4];
+  float              dither_b[OP_NCHANNELS_MAX*4];
+  opus_uint32        dither_seed;
+  int                dither_mute;
+  int                dither_disabled;
+  /*The number of channels represented by the internal state.
+    This gets set to 0 whenever anything that would prevent state propagation
+     occurs (switching between the float/short APIs, or between the
+     stereo/multistream APIs).*/
+  int                state_channel_count;
+#endif
+};
+
+int op_strncasecmp(const char *_a,const char *_b,int _n);
+
+#endif
diff --git a/opusfile/opusfile.c b/opusfile/opusfile.c
new file mode 100644
index 0000000..3894ffd
--- /dev/null
+++ b/opusfile/opusfile.c
@@ -0,0 +1,3326 @@
+/********************************************************************
+ *                                                                  *
+ * THIS FILE IS PART OF THE libopusfile SOFTWARE CODEC SOURCE CODE. *
+ * USE, DISTRIBUTION AND REPRODUCTION OF THIS LIBRARY SOURCE IS     *
+ * GOVERNED BY A BSD-STYLE SOURCE LICENSE INCLUDED WITH THIS SOURCE *
+ * IN 'COPYING'. PLEASE READ THESE TERMS BEFORE DISTRIBUTING.       *
+ *                                                                  *
+ * THE libopusfile SOURCE CODE IS (C) COPYRIGHT 1994-2012           *
+ * by the Xiph.Org Foundation and contributors http://www.xiph.org/ *
+ *                                                                  *
+ ********************************************************************
+
+ function: stdio-based convenience library for opening/seeking/decoding
+ last mod: $Id: vorbisfile.c 17573 2010-10-27 14:53:59Z xiphmont $
+
+ ********************************************************************/
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "internal.h"
+#include <stdio.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <limits.h>
+#include <string.h>
+#include <math.h>
+
+#include "opusfile.h"
+
+/*This implementation is largely based off of libvorbisfile.
+  All of the Ogg bits work roughly the same, though I have made some
+   "improvements" that have not been folded back there, yet.*/
+
+/*A 'chained bitstream' is an Ogg Opus bitstream that contains more than one
+   logical bitstream arranged end to end (the only form of Ogg multiplexing
+   supported by this library.
+  Grouping (parallel multiplexing) is not supported, except to the extent that
+   if there are multiple logical Ogg streams in a single link of the chain, we
+   will ignore all but the first Opus stream we find.*/
+
+/*An Ogg Opus file can be played beginning to end (streamed) without worrying
+   ahead of time about chaining (see opusdec from the opus-tools package).
+  If we have the whole file, however, and want random access
+   (seeking/scrubbing) or desire to know the total length/time of a file, we
+   need to account for the possibility of chaining.*/
+
+/*We can handle things a number of ways.
+  We can determine the entire bitstream structure right off the bat, or find
+   pieces on demand.
+  This library determines and caches structure for the entire bitstream, but
+   builds a virtual decoder on the fly when moving between links in the chain.*/
+
+/*There are also different ways to implement seeking.
+  Enough information exists in an Ogg bitstream to seek to sample-granularity
+   positions in the output.
+  Or, one can seek by picking some portion of the stream roughly in the desired
+   area if we only want coarse navigation through the stream.
+  We implement and expose both strategies.*/
+
+/*The maximum number of bytes in a page (including the page headers).*/
+#define OP_PAGE_SIZE_MAX  (65307)
+/*The default amount to seek backwards per step when trying to find the
+   previous page.
+  This must be at least as large as the maximum size of a page.*/
+#define OP_CHUNK_SIZE     (65536)
+/*The maximum amount to seek backwards per step when trying to find the
+   previous page.*/
+#define OP_CHUNK_SIZE_MAX (1024*(opus_int32)1024)
+/*A smaller read size is needed for low-rate streaming.*/
+#define OP_READ_SIZE      (2048)
+
+int op_test(OpusHead *_head,
+ const unsigned char *_initial_data,size_t _initial_bytes){
+  ogg_sync_state  oy;
+  char           *data;
+  int             err;
+  /*The first page of a normal Opus file will be at most 57 bytes (27 Ogg
+     page header bytes + 1 lacing value + 21 Opus header bytes + 8 channel
+     mapping bytes).
+    It will be at least 47 bytes (27 Ogg page header bytes + 1 lacing value +
+     19 Opus header bytes using channel mapping family 0).
+    If we don't have at least that much data, give up now.*/
+  if(_initial_bytes<47)return OP_FALSE;
+  /*Only proceed if we start with the magic OggS string.
+    This is to prevent us spending a lot of time allocating memory and looking
+     for Ogg pages in non-Ogg files.*/
+  if(memcmp(_initial_data,"OggS",4)!=0)return OP_ENOTFORMAT;
+  if(OP_UNLIKELY(_initial_bytes>(size_t)LONG_MAX))return OP_EFAULT;
+  ogg_sync_init(&oy);
+  data=ogg_sync_buffer(&oy,(long)_initial_bytes);
+  if(data!=NULL){
+    ogg_stream_state os;
+    ogg_page         og;
+    int              ret;
+    memcpy(data,_initial_data,_initial_bytes);
+    ogg_sync_wrote(&oy,(long)_initial_bytes);
+    ogg_stream_init(&os,-1);
+    err=OP_FALSE;
+    do{
+      ogg_packet op;
+      ret=ogg_sync_pageout(&oy,&og);
+      /*Ignore holes.*/
+      if(ret<0)continue;
+      /*Stop if we run out of data.*/
+      if(!ret)break;
+      ogg_stream_reset_serialno(&os,ogg_page_serialno(&og));
+      ogg_stream_pagein(&os,&og);
+      /*Only process the first packet on this page (if it's a BOS packet,
+         it's required to be the only one).*/
+      if(ogg_stream_packetout(&os,&op)==1){
+        if(op.b_o_s){
+          ret=opus_head_parse(_head,op.packet,op.bytes);
+          /*If this didn't look like Opus, keep going.*/
+          if(ret==OP_ENOTFORMAT)continue;
+          /*Otherwise we're done, one way or another.*/
+          err=ret;
+        }
+        /*We finished parsing the headers.
+          There is no Opus to be found.*/
+        else err=OP_ENOTFORMAT;
+      }
+    }
+    while(err==OP_FALSE);
+    ogg_stream_clear(&os);
+  }
+  else err=OP_EFAULT;
+  ogg_sync_clear(&oy);
+  return err;
+}
+
+/*Many, many internal helpers.
+  The intention is not to be confusing.
+  Rampant duplication and monolithic function implementation (though we do have
+   some large, omnibus functions still) would be harder to understand anyway.
+  The high level functions are last.
+  Begin grokking near the end of the file if you prefer to read things
+   top-down.*/
+
+/*The read/seek functions track absolute position within the stream.*/
+
+/*Read a little more data from the file/pipe into the ogg_sync framer.
+  _nbytes: The maximum number of bytes to read.
+  Return: A positive number of bytes read on success, 0 on end-of-file, or a
+           negative value on failure.*/
+static int op_get_data(OggOpusFile *_of,int _nbytes){
+  unsigned char *buffer;
+  int            nbytes;
+  OP_ASSERT(_nbytes>0);
+  buffer=(unsigned char *)ogg_sync_buffer(&_of->oy,_nbytes);
+  nbytes=(int)(*_of->callbacks.read)(_of->stream,buffer,_nbytes);
+  OP_ASSERT(nbytes<=_nbytes);
+  if(OP_LIKELY(nbytes>0))ogg_sync_wrote(&_of->oy,nbytes);
+  return nbytes;
+}
+
+/*Save a tiny smidge of verbosity to make the code more readable.*/
+static int op_seek_helper(OggOpusFile *_of,opus_int64 _offset){
+  if(_offset==_of->offset)return 0;
+  if(_of->callbacks.seek==NULL
+   ||(*_of->callbacks.seek)(_of->stream,_offset,SEEK_SET)){
+    return OP_EREAD;
+  }
+  _of->offset=_offset;
+  ogg_sync_reset(&_of->oy);
+  return 0;
+}
+
+/*Get the current position indicator of the underlying stream.
+  This should be the same as the value reported by tell().*/
+static opus_int64 op_position(const OggOpusFile *_of){
+  /*The current position indicator is _not_ simply offset.
+    We may also have unprocessed, buffered data in the sync state.*/
+  return _of->offset+_of->oy.fill-_of->oy.returned;
+}
+
+/*From the head of the stream, get the next page.
+  _boundary specifies if the function is allowed to fetch more data from the
+   stream (and how much) or only use internally buffered data.
+  _boundary: -1: Unbounded search.
+              0: Read no additional data.
+                 Use only cached data.
+              n: Search for the start of a new page up to file position n.
+  Return: n>=0:       Found a page at absolute offset n.
+          OP_FALSE:   Hit the _boundary limit.
+          OP_EREAD:   An underlying read operation failed.
+          OP_BADLINK: We hit end-of-file before reaching _boundary.*/
+static opus_int64 op_get_next_page(OggOpusFile *_of,ogg_page *_og,
+ opus_int64 _boundary){
+  while(_boundary<=0||_of->offset<_boundary){
+    int more;
+    more=ogg_sync_pageseek(&_of->oy,_og);
+    /*Skipped (-more) bytes.*/
+    if(OP_UNLIKELY(more<0))_of->offset-=more;
+    else if(more==0){
+      int read_nbytes;
+      int ret;
+      /*Send more paramedics.*/
+      if(!_boundary)return OP_FALSE;
+      if(_boundary<0)read_nbytes=OP_READ_SIZE;
+      else{
+        opus_int64 position;
+        position=op_position(_of);
+        if(position>=_boundary)return OP_FALSE;
+        read_nbytes=(int)OP_MIN(_boundary-position,OP_READ_SIZE);
+      }
+      ret=op_get_data(_of,read_nbytes);
+      if(OP_UNLIKELY(ret<0))return OP_EREAD;
+      if(OP_UNLIKELY(ret==0)){
+        /*Only fail cleanly on EOF if we didn't have a known boundary.
+          Otherwise, we should have been able to reach that boundary, and this
+           is a fatal error.*/
+        return OP_UNLIKELY(_boundary<0)?OP_FALSE:OP_EBADLINK;
+      }
+    }
+    else{
+      /*Got a page.
+        Return the page start offset and advance the internal offset past the
+         page end.*/
+      opus_int64 page_offset;
+      page_offset=_of->offset;
+      _of->offset+=more;
+      OP_ASSERT(page_offset>=0);
+      return page_offset;
+    }
+  }
+  return OP_FALSE;
+}
+
+static int op_add_serialno(const ogg_page *_og,
+ ogg_uint32_t **_serialnos,int *_nserialnos,int *_cserialnos){
+  ogg_uint32_t *serialnos;
+  int           nserialnos;
+  int           cserialnos;
+  ogg_uint32_t s;
+  s=ogg_page_serialno(_og);
+  serialnos=*_serialnos;
+  nserialnos=*_nserialnos;
+  cserialnos=*_cserialnos;
+  if(OP_UNLIKELY(nserialnos>=cserialnos)){
+    if(OP_UNLIKELY(cserialnos>INT_MAX/(int)sizeof(*serialnos)-1>>1)){
+      return OP_EFAULT;
+    }
+    cserialnos=2*cserialnos+1;
+    OP_ASSERT(nserialnos<cserialnos);
+    serialnos=(ogg_uint32_t *)_ogg_realloc(serialnos,
+     sizeof(*serialnos)*cserialnos);
+    if(OP_UNLIKELY(serialnos==NULL))return OP_EFAULT;
+  }
+  serialnos[nserialnos++]=s;
+  *_serialnos=serialnos;
+  *_nserialnos=nserialnos;
+  *_cserialnos=cserialnos;
+  return 0;
+}
+
+/*Returns nonzero if found.*/
+static int op_lookup_serialno(ogg_uint32_t _s,
+ const ogg_uint32_t *_serialnos,int _nserialnos){
+  int i;
+  for(i=0;i<_nserialnos&&_serialnos[i]!=_s;i++);
+  return i<_nserialnos;
+}
+
+static int op_lookup_page_serialno(const ogg_page *_og,
+ const ogg_uint32_t *_serialnos,int _nserialnos){
+  return op_lookup_serialno(ogg_page_serialno(_og),_serialnos,_nserialnos);
+}
+
+typedef struct OpusSeekRecord OpusSeekRecord;
+
+/*We use this to remember the pages we found while enumerating the links of a
+   chained stream.
+  We keep track of the starting and ending offsets, as well as the point we
+   started searching from, so we know where to bisect.
+  We also keep the serial number, so we can tell if the page belonged to the
+   current link or not, as well as the granule position, to aid in estimating
+   the start of the link.*/
+struct OpusSeekRecord{
+  /*The earliest byte we know of such that reading forward from it causes
+     capture to be regained at this page.*/
+  opus_int64   search_start;
+  /*The offset of this page.*/
+  opus_int64   offset;
+  /*The size of this page.*/
+  opus_int32   size;
+  /*The serial number of this page.*/
+  ogg_uint32_t serialno;
+  /*The granule position of this page.*/
+  ogg_int64_t  gp;
+};
+
+/*Find the last page beginning before _offset with a valid granule position.
+  There is no '_boundary' parameter as it will always have to read more data.
+  This is much dirtier than the above, as Ogg doesn't have any backward search
+   linkage.
+  This search prefers pages of the specified serial number.
+  If a page of the specified serial number is spotted during the
+   seek-back-and-read-forward, it will return the info of last page of the
+   matching serial number, instead of the very last page, unless the very last
+   page belongs to a different link than preferred serial number.
+  If no page of the specified serial number is seen, it will return the info of
+   the last page.
+  [out] _sr:   Returns information about the page that was found on success.
+  _offset:     The _offset before which to find a page.
+               Any page returned will consist of data entirely before _offset.
+  _serialno:   The preferred serial number.
+               If a page with this serial number is found, it will be returned
+                even if another page in the same link is found closer to
+                _offset.
+               This is purely opportunistic: there is no guarantee such a page
+                will be found if it exists.
+  _serialnos:  The list of serial numbers in the link that contains the
+                preferred serial number.
+  _nserialnos: The number of serial numbers in the current link.
+  Return: 0 on success, or a negative value on failure.
+          OP_EREAD:    Failed to read more data (error or EOF).
+          OP_EBADLINK: We couldn't find a page even after seeking back to the
+                        start of the stream.*/
+static int op_get_prev_page_serial(OggOpusFile *_of,OpusSeekRecord *_sr,
+ opus_int64 _offset,ogg_uint32_t _serialno,
+ const ogg_uint32_t *_serialnos,int _nserialnos){
+  OpusSeekRecord preferred_sr;
+  ogg_page       og;
+  opus_int64     begin;
+  opus_int64     end;
+  opus_int64     original_end;
+  opus_int32     chunk_size;
+  int            preferred_found;
+  original_end=end=begin=_offset;
+  preferred_found=0;
+  _offset=-1;
+  chunk_size=OP_CHUNK_SIZE;
+  do{
+    opus_int64 search_start;
+    int        ret;
+    OP_ASSERT(chunk_size>=OP_PAGE_SIZE_MAX);
+    begin=OP_MAX(begin-chunk_size,0);
+    ret=op_seek_helper(_of,begin);
+    if(OP_UNLIKELY(ret<0))return ret;
+    search_start=begin;
+    while(_of->offset<end){
+      opus_int64   llret;
+      ogg_uint32_t serialno;
+      llret=op_get_next_page(_of,&og,end);
+      if(OP_UNLIKELY(llret<OP_FALSE))return (int)llret;
+      else if(llret==OP_FALSE)break;
+      serialno=ogg_page_serialno(&og);
+      /*Save the information for this page.
+        We're not interested in the page itself... just the serial number, byte
+         offset, page size, and granule position.*/
+      _sr->search_start=search_start;
+      _sr->offset=_offset=llret;
+      _sr->serialno=serialno;
+      OP_ASSERT(_of->offset-_offset>=0);
+      OP_ASSERT(_of->offset-_offset<=OP_PAGE_SIZE_MAX);
+      _sr->size=(opus_int32)(_of->offset-_offset);
+      _sr->gp=ogg_page_granulepos(&og);
+      /*If this page is from the stream we're looking for, remember it.*/
+      if(serialno==_serialno){
+        preferred_found=1;
+        *&preferred_sr=*_sr;
+      }
+      if(!op_lookup_serialno(serialno,_serialnos,_nserialnos)){
+        /*We fell off the end of the link, which means we seeked back too far
+           and shouldn't have been looking in that link to begin with.
+          If we found the preferred serial number, forget that we saw it.*/
+        preferred_found=0;
+      }
+      search_start=llret+1;
+    }
+    /*We started from the beginning of the stream and found nothing.
+      This should be impossible unless the contents of the stream changed out
+       from under us after we read from it.*/
+    if(OP_UNLIKELY(!begin)&&OP_UNLIKELY(_offset<0))return OP_EBADLINK;
+    /*Bump up the chunk size.
+      This is mildly helpful when seeks are very expensive (http).*/
+    chunk_size=OP_MIN(2*chunk_size,OP_CHUNK_SIZE_MAX);
+    /*Avoid quadratic complexity if we hit an invalid patch of the file.*/
+    end=OP_MIN(begin+OP_PAGE_SIZE_MAX-1,original_end);
+  }
+  while(_offset<0);
+  if(preferred_found)*_sr=*&preferred_sr;
+  return 0;
+}
+
+/*Find the last page beginning before _offset with the given serial number and
+   a valid granule position.
+  Unlike the above search, this continues until it finds such a page, but does
+   not stray outside the current link.
+  We could implement it (inefficiently) by calling op_get_prev_page_serial()
+   repeatedly until it returned a page that had both our preferred serial
+   number and a valid granule position, but doing it with a separate function
+   allows us to avoid repeatedly re-scanning valid pages from other streams as
+   we seek-back-and-read-forward.
+  [out] _gp:   Returns the granule position of the page that was found on
+                success.
+  _offset:     The _offset before which to find a page.
+               Any page returned will consist of data entirely before _offset.
+  _serialno:   The target serial number.
+  _serialnos:  The list of serial numbers in the link that contains the
+                preferred serial number.
+  _nserialnos: The number of serial numbers in the current link.
+  Return: The offset of the page on success, or a negative value on failure.
+          OP_EREAD:    Failed to read more data (error or EOF).
+          OP_EBADLINK: We couldn't find a page even after seeking back past the
+                        beginning of the link.*/
+static opus_int64 op_get_last_page(OggOpusFile *_of,ogg_int64_t *_gp,
+ opus_int64 _offset,ogg_uint32_t _serialno,
+ const ogg_uint32_t *_serialnos,int _nserialnos){
+  ogg_page    og;
+  ogg_int64_t gp;
+  opus_int64  begin;
+  opus_int64  end;
+  opus_int64  original_end;
+  opus_int32  chunk_size;
+  /*The target serial number must belong to the current link.*/
+  OP_ASSERT(op_lookup_serialno(_serialno,_serialnos,_nserialnos));
+  original_end=end=begin=_offset;
+  _offset=-1;
+  /*We shouldn't have to initialize gp, but gcc is too dumb to figure out that
+     ret>=0 implies we entered the if(page_gp!=-1) block at least once.*/
+  gp=-1;
+  chunk_size=OP_CHUNK_SIZE;
+  do{
+    int left_link;
+    int ret;
+    OP_ASSERT(chunk_size>=OP_PAGE_SIZE_MAX);
+    begin=OP_MAX(begin-chunk_size,0);
+    ret=op_seek_helper(_of,begin);
+    if(OP_UNLIKELY(ret<0))return ret;
+    left_link=0;
+    while(_of->offset<end){
+      opus_int64   llret;
+      ogg_uint32_t serialno;
+      llret=op_get_next_page(_of,&og,end);
+      if(OP_UNLIKELY(llret<OP_FALSE))return llret;
+      else if(llret==OP_FALSE)break;
+      serialno=ogg_page_serialno(&og);
+      if(serialno==_serialno){
+        ogg_int64_t page_gp;
+        /*The page is from the right stream...*/
+        page_gp=ogg_page_granulepos(&og);
+        if(page_gp!=-1){
+          /*And has a valid granule position.
+            Let's remember it.*/
+          _offset=llret;
+          gp=page_gp;
+        }
+      }
+      else if(OP_UNLIKELY(!op_lookup_serialno(serialno,
+       _serialnos,_nserialnos))){
+        /*We fell off the start of the link, which means we don't need to keep
+           seeking any farther back.*/
+        left_link=1;
+      }
+    }
+    /*We started from at or before the beginning of the link and found nothing.
+      This should be impossible unless the contents of the stream changed out
+       from under us after we read from it.*/
+    if((OP_UNLIKELY(left_link)||OP_UNLIKELY(!begin))&&OP_UNLIKELY(_offset<0)){
+      return OP_EBADLINK;
+    }
+    /*Bump up the chunk size.
+      This is mildly helpful when seeks are very expensive (http).*/
+    chunk_size=OP_MIN(2*chunk_size,OP_CHUNK_SIZE_MAX);
+    /*Avoid quadratic complexity if we hit an invalid patch of the file.*/
+    end=OP_MIN(begin+OP_PAGE_SIZE_MAX-1,original_end);
+  }
+  while(_offset<0);
+  *_gp=gp;
+  return _offset;
+}
+
+/*Uses the local ogg_stream storage in _of.
+  This is important for non-streaming input sources.*/
+static int op_fetch_headers_impl(OggOpusFile *_of,OpusHead *_head,
+ OpusTags *_tags,ogg_uint32_t **_serialnos,int *_nserialnos,
+ int *_cserialnos,ogg_page *_og){
+  ogg_packet op;
+  int        ret;
+  if(_serialnos!=NULL)*_nserialnos=0;
+  /*Extract the serialnos of all BOS pages plus the first set of Opus headers
+     we see in the link.*/
+  while(ogg_page_bos(_og)){
+    if(_serialnos!=NULL){
+      if(OP_UNLIKELY(op_lookup_page_serialno(_og,*_serialnos,*_nserialnos))){
+        /*A dupe serialnumber in an initial header packet set==invalid stream.*/
+        return OP_EBADHEADER;
+      }
+      ret=op_add_serialno(_og,_serialnos,_nserialnos,_cserialnos);
+      if(OP_UNLIKELY(ret<0))return ret;
+    }
+    if(_of->ready_state<OP_STREAMSET){
+      /*We don't have an Opus stream in this link yet, so begin prospective
+         stream setup.
+        We need a stream to get packets.*/
+      ogg_stream_reset_serialno(&_of->os,ogg_page_serialno(_og));
+      ogg_stream_pagein(&_of->os,_og);
+      if(OP_LIKELY(ogg_stream_packetout(&_of->os,&op)>0)){
+        ret=opus_head_parse(_head,op.packet,op.bytes);
+        /*Found a valid Opus header.
+          Continue setup.*/
+        if(OP_LIKELY(ret>=0))_of->ready_state=OP_STREAMSET;
+        /*If it's just a stream type we don't recognize, ignore it.
+          Everything else is fatal.*/
+        else if(ret!=OP_ENOTFORMAT)return ret;
+      }
+      /*TODO: Should a BOS page with no packets be an error?*/
+    }
+    /*Get the next page.
+      No need to clamp the boundary offset against _of->end, as all errors
+       become OP_ENOTFORMAT or OP_EBADHEADER.*/
+    if(OP_UNLIKELY(op_get_next_page(_of,_og,
+     OP_ADV_OFFSET(_of->offset,OP_CHUNK_SIZE))<0)){
+      return _of->ready_state<OP_STREAMSET?OP_ENOTFORMAT:OP_EBADHEADER;
+    }
+  }
+  if(OP_UNLIKELY(_of->ready_state!=OP_STREAMSET))return OP_ENOTFORMAT;
+  /*If the first non-header page belonged to our Opus stream, submit it.*/
+  if(_of->os.serialno==ogg_page_serialno(_og))ogg_stream_pagein(&_of->os,_og);
+  /*Loop getting packets.*/
+  for(;;){
+    switch(ogg_stream_packetout(&_of->os,&op)){
+      case 0:{
+        /*Loop getting pages.*/
+        for(;;){
+          /*No need to clamp the boundary offset against _of->end, as all
+             errors become OP_EBADHEADER.*/
+          if(OP_UNLIKELY(op_get_next_page(_of,_og,
+           OP_ADV_OFFSET(_of->offset,OP_CHUNK_SIZE))<0)){
+            return OP_EBADHEADER;
+          }
+          /*If this page belongs to the correct stream, go parse it.*/
+          if(_of->os.serialno==ogg_page_serialno(_og)){
+            ogg_stream_pagein(&_of->os,_og);
+            break;
+          }
+          /*If the link ends before we see the Opus comment header, abort.*/
+          if(OP_UNLIKELY(ogg_page_bos(_og)))return OP_EBADHEADER;
+          /*Otherwise, keep looking.*/
+        }
+      }break;
+      /*We shouldn't get a hole in the headers!*/
+      case -1:return OP_EBADHEADER;
+      default:{
+        /*Got a packet.
+          It should be the comment header.*/
+        ret=opus_tags_parse(_tags,op.packet,op.bytes);
+        if(OP_UNLIKELY(ret<0))return ret;
+        /*Make sure the page terminated at the end of the comment header.
+          If there is another packet on the page, or part of a packet, then
+           reject the stream.
+          Otherwise seekable sources won't be able to seek back to the start
+           properly.*/
+        ret=ogg_stream_packetout(&_of->os,&op);
+        if(OP_UNLIKELY(ret!=0)
+         ||OP_UNLIKELY(_og->header[_og->header_len-1]==255)){
+          /*If we fail, the caller assumes our tags are uninitialized.*/
+          opus_tags_clear(_tags);
+          return OP_EBADHEADER;
+        }
+        return 0;
+      }
+    }
+  }
+}
+
+static int op_fetch_headers(OggOpusFile *_of,OpusHead *_head,
+ OpusTags *_tags,ogg_uint32_t **_serialnos,int *_nserialnos,
+ int *_cserialnos,ogg_page *_og){
+  ogg_page og;
+  int      ret;
+  if(!_og){
+    /*No need to clamp the boundary offset against _of->end, as all errors
+       become OP_ENOTFORMAT.*/
+    if(OP_UNLIKELY(op_get_next_page(_of,&og,
+     OP_ADV_OFFSET(_of->offset,OP_CHUNK_SIZE))<0)){
+      return OP_ENOTFORMAT;
+    }
+    _og=&og;
+  }
+  _of->ready_state=OP_OPENED;
+  ret=op_fetch_headers_impl(_of,_head,_tags,_serialnos,_nserialnos,
+   _cserialnos,_og);
+  /*Revert back from OP_STREAMSET to OP_OPENED on failure, to prevent
+     double-free of the tags in an unseekable stream.*/
+  if(OP_UNLIKELY(ret<0))_of->ready_state=OP_OPENED;
+  return ret;
+}
+
+/*Granule position manipulation routines.
+  A granule position is defined to be an unsigned 64-bit integer, with the
+   special value -1 in two's complement indicating an unset or invalid granule
+   position.
+  We are not guaranteed to have an unsigned 64-bit type, so we construct the
+   following routines that
+   a) Properly order negative numbers as larger than positive numbers, and
+   b) Check for underflow or overflow past the special -1 value.
+  This lets us operate on the full, valid range of granule positions in a
+   consistent and safe manner.
+  This full range is organized into distinct regions:
+   [ -1 (invalid) ][ 0 ... OP_INT64_MAX ][ OP_INT64_MIN ... -2 ][-1 (invalid) ]
+
+  No one should actually use granule positions so large that they're negative,
+   even if they are technically valid, as very little software handles them
+   correctly (including most of Xiph.Org's).
+  This library also refuses to support durations so large they won't fit in a
+   signed 64-bit integer (to avoid exposing this mess to the application, and
+   to simplify a good deal of internal arithmetic), so the only way to use them
+   successfully is if pcm_start is very large.
+  This means there isn't anything you can do with negative granule positions
+   that you couldn't have done with purely non-negative ones.
+  The main purpose of these routines is to allow us to think very explicitly
+   about the possible failure cases of all granule position manipulations.*/
+
+/*Safely adds a small signed integer to a valid (not -1) granule position.
+  The result can use the full 64-bit range of values (both positive and
+   negative), but will fail on overflow (wrapping past -1; wrapping past
+   OP_INT64_MAX is explicitly okay).
+  [out] _dst_gp: The resulting granule position.
+                 Only modified on success.
+  _src_gp:       The granule position to add to.
+                 This must not be -1.
+  _delta:        The amount to add.
+                 This is allowed to be up to 32 bits to support the maximum
+                  duration of a single Ogg page (255 packets * 120 ms per
+                  packet == 1,468,800 samples at 48 kHz).
+  Return: 0 on success, or OP_EINVAL if the result would wrap around past -1.*/
+static int op_granpos_add(ogg_int64_t *_dst_gp,ogg_int64_t _src_gp,
+ opus_int32 _delta){
+  /*The code below handles this case correctly, but there's no reason we
+     should ever be called with these values, so make sure we aren't.*/
+  OP_ASSERT(_src_gp!=-1);
+  if(_delta>0){
+    /*Adding this amount to the granule position would overflow its 64-bit
+       range.*/
+    if(OP_UNLIKELY(_src_gp<0)&&OP_UNLIKELY(_src_gp>=-1-_delta))return OP_EINVAL;
+    if(OP_UNLIKELY(_src_gp>OP_INT64_MAX-_delta)){
+      /*Adding this amount to the granule position would overflow the positive
+         half of its 64-bit range.
+        Since signed overflow is undefined in C, do it in a way the compiler
+         isn't allowed to screw up.*/
+      _delta-=(opus_int32)(OP_INT64_MAX-_src_gp)+1;
+      _src_gp=OP_INT64_MIN;
+    }
+  }
+  else if(_delta<0){
+    /*Subtracting this amount from the granule position would underflow its
+       64-bit range.*/
+    if(_src_gp>=0&&OP_UNLIKELY(_src_gp<-_delta))return OP_EINVAL;
+    if(OP_UNLIKELY(_src_gp<OP_INT64_MIN-_delta)){
+      /*Subtracting this amount from the granule position would underflow the
+         negative half of its 64-bit range.
+        Since signed underflow is undefined in C, do it in a way the compiler
+         isn't allowed to screw up.*/
+      _delta+=(opus_int32)(_src_gp-OP_INT64_MIN)+1;
+      _src_gp=OP_INT64_MAX;
+    }
+  }
+  *_dst_gp=_src_gp+_delta;
+  return 0;
+}
+
+/*Safely computes the difference between two granule positions.
+  The difference must fit in a signed 64-bit integer, or the function fails.
+  It correctly handles the case where the granule position has wrapped around
+   from positive values to negative ones.
+  [out] _delta: The difference between the granule positions.
+                Only modified on success.
+  _gp_a:        The granule position to subtract from.
+                This must not be -1.
+  _gp_b:        The granule position to subtract.
+                This must not be -1.
+  Return: 0 on success, or OP_EINVAL if the result would not fit in a signed
+           64-bit integer.*/
+static int op_granpos_diff(ogg_int64_t *_delta,
+ ogg_int64_t _gp_a,ogg_int64_t _gp_b){
+  int gp_a_negative;
+  int gp_b_negative;
+  /*The code below handles these cases correctly, but there's no reason we
+     should ever be called with these values, so make sure we aren't.*/
+  OP_ASSERT(_gp_a!=-1);
+  OP_ASSERT(_gp_b!=-1);
+  gp_a_negative=OP_UNLIKELY(_gp_a<0);
+  gp_b_negative=OP_UNLIKELY(_gp_b<0);
+  if(OP_UNLIKELY(gp_a_negative^gp_b_negative)){
+    ogg_int64_t da;
+    ogg_int64_t db;
+    if(gp_a_negative){
+      /*_gp_a has wrapped to a negative value but _gp_b hasn't: the difference
+         should be positive.*/
+      /*Step 1: Handle wrapping.*/
+      /*_gp_a < 0 => da < 0.*/
+      da=(OP_INT64_MIN-_gp_a)-1;
+      /*_gp_b >= 0  => db >= 0.*/
+      db=OP_INT64_MAX-_gp_b;
+      /*Step 2: Check for overflow.*/
+      if(OP_UNLIKELY(OP_INT64_MAX+da<db))return OP_EINVAL;
+      *_delta=db-da;
+    }
+    else{
+      /*_gp_b has wrapped to a negative value but _gp_a hasn't: the difference
+         should be negative.*/
+      /*Step 1: Handle wrapping.*/
+      /*_gp_a >= 0 => da <= 0*/
+      da=_gp_a+OP_INT64_MIN;
+      /*_gp_b < 0 => db <= 0*/
+      db=OP_INT64_MIN-_gp_b;
+      /*Step 2: Check for overflow.*/
+      if(OP_UNLIKELY(da<OP_INT64_MIN-db))return OP_EINVAL;
+      *_delta=da+db;
+    }
+  }
+  else *_delta=_gp_a-_gp_b;
+  return 0;
+}
+
+static int op_granpos_cmp(ogg_int64_t _gp_a,ogg_int64_t _gp_b){
+  /*The invalid granule position -1 should behave like NaN: neither greater
+     than nor less than any other granule position, nor equal to any other
+     granule position, including itself.
+    However, that means there isn't anything we could sensibly return from this
+     function for it.*/
+  OP_ASSERT(_gp_a!=-1);
+  OP_ASSERT(_gp_b!=-1);
+  /*Handle the wrapping cases.*/
+  if(OP_UNLIKELY(_gp_a<0)){
+    if(_gp_b>=0)return 1;
+    /*Else fall through.*/
+  }
+  else if(OP_UNLIKELY(_gp_b<0))return -1;
+  /*No wrapping case.*/
+  return (_gp_a>_gp_b)-(_gp_b>_gp_a);
+}
+
+/*Returns the duration of the packet (in samples at 48 kHz), or a negative
+   value on error.*/
+static int op_get_packet_duration(const unsigned char *_data,int _len){
+  int nframes;
+  int frame_size;
+  int nsamples;
+  nframes=opus_packet_get_nb_frames(_data,_len);
+  if(OP_UNLIKELY(nframes<0))return OP_EBADPACKET;
+  frame_size=opus_packet_get_samples_per_frame(_data,48000);
+  nsamples=nframes*frame_size;
+  if(OP_UNLIKELY(nsamples>120*48))return OP_EBADPACKET;
+  return nsamples;
+}
+
+/*This function more properly belongs in info.c, but we define it here to allow
+   the static granule position manipulation functions to remain static.*/
+ogg_int64_t opus_granule_sample(const OpusHead *_head,ogg_int64_t _gp){
+  opus_int32 pre_skip;
+  pre_skip=_head->pre_skip;
+  if(_gp!=-1&&op_granpos_add(&_gp,_gp,-pre_skip))_gp=-1;
+  return _gp;
+}
+
+/*Grab all the packets currently in the stream state, and compute their
+   durations.
+  _of->op_count is set to the number of packets collected.
+  [out] _durations: Returns the durations of the individual packets.
+  Return: The total duration of all packets, or OP_HOLE if there was a hole.*/
+static opus_int32 op_collect_audio_packets(OggOpusFile *_of,
+ int _durations[255]){
+  opus_int32 total_duration;
+  int        op_count;
+  /*Count the durations of all packets in the page.*/
+  op_count=0;
+  total_duration=0;
+  for(;;){
+    int ret;
+    /*This takes advantage of undocumented libogg behavior that returned
+       ogg_packet buffers are valid at least until the next page is
+       submitted.
+      Relying on this is not too terrible, as _none_ of the Ogg memory
+       ownership/lifetime rules are well-documented.
+      But I can read its code and know this will work.*/
+    ret=ogg_stream_packetout(&_of->os,_of->op+op_count);
+    if(!ret)break;
+    if(OP_UNLIKELY(ret<0)){
+      /*We shouldn't get holes in the middle of pages.*/
+      OP_ASSERT(op_count==0);
+      /*Set the return value and break out of the loop.
+        We want to make sure op_count gets set to 0, because we've ingested a
+         page, so any previously loaded packets are now invalid.*/
+      total_duration=OP_HOLE;
+      break;
+    }
+    /*Unless libogg is broken, we can't get more than 255 packets from a
+       single page.*/
+    OP_ASSERT(op_count<255);
+    _durations[op_count]=op_get_packet_duration(_of->op[op_count].packet,
+     _of->op[op_count].bytes);
+    if(OP_LIKELY(_durations[op_count]>0)){
+      /*With at most 255 packets on a page, this can't overflow.*/
+      total_duration+=_durations[op_count++];
+    }
+    /*Ignore packets with an invalid TOC sequence.*/
+    else if(op_count>0){
+      /*But save the granule position, if there was one.*/
+      _of->op[op_count-1].granulepos=_of->op[op_count].granulepos;
+    }
+  }
+  _of->op_pos=0;
+  _of->op_count=op_count;
+  return total_duration;
+}
+
+/*Starting from current cursor position, get the initial PCM offset of the next
+   page.
+  This also validates the granule position on the first page with a completed
+   audio data packet, as required by the spec.
+  If this link is completely empty (no pages with completed packets), then this
+   function sets pcm_start=pcm_end=0 and returns the BOS page of the next link
+   (if any).
+  In the seekable case, we initialize pcm_end=-1 before calling this function,
+   so that later we can detect that the link was empty before calling
+   op_find_final_pcm_offset().
+  [inout] _link: The link for which to find pcm_start.
+  [out] _og:     Returns the BOS page of the next link if this link was empty.
+                 In the unseekable case, we can then feed this to
+                  op_fetch_headers() to start the next link.
+                 The caller may pass NULL (e.g., for seekable streams), in
+                  which case this page will be discarded.
+  Return: 0 on success, 1 if there is a buffered BOS page available, or a
+           negative value on unrecoverable error.*/
+static int op_find_initial_pcm_offset(OggOpusFile *_of,
+ OggOpusLink *_link,ogg_page *_og){
+  ogg_page     og;
+  opus_int64   page_offset;
+  ogg_int64_t  pcm_start;
+  ogg_int64_t  prev_packet_gp;
+  ogg_int64_t  cur_page_gp;
+  ogg_uint32_t serialno;
+  opus_int32   total_duration;
+  int          durations[255];
+  int          cur_page_eos;
+  int          op_count;
+  int          pi;
+  if(_og==NULL)_og=&og;
+  serialno=_of->os.serialno;
+  op_count=0;
+  /*We shouldn't have to initialize total_duration, but gcc is too dumb to
+     figure out that op_count>0 implies we've been through the whole loop at
+     least once.*/
+  total_duration=0;
+  do{
+    page_offset=op_get_next_page(_of,_og,_of->end);
+    /*We should get a page unless the file is truncated or mangled.
+      Otherwise there are no audio data packets in the whole logical stream.*/
+    if(OP_UNLIKELY(page_offset<0)){
+      /*Fail if there was a read error.*/
+      if(page_offset<OP_FALSE)return (int)page_offset;
+      /*Fail if the pre-skip is non-zero, since it's asking us to skip more
+         samples than exist.*/
+      if(_link->head.pre_skip>0)return OP_EBADTIMESTAMP;
+      _link->pcm_file_offset=0;
+      /*Set pcm_end and end_offset so we can skip the call to
+         op_find_final_pcm_offset().*/
+      _link->pcm_start=_link->pcm_end=0;
+      _link->end_offset=_link->data_offset;
+      return 0;
+    }
+    /*Similarly, if we hit the next link in the chain, we've gone too far.*/
+    if(OP_UNLIKELY(ogg_page_bos(_og))){
+      if(_link->head.pre_skip>0)return OP_EBADTIMESTAMP;
+      /*Set pcm_end and end_offset so we can skip the call to
+         op_find_final_pcm_offset().*/
+      _link->pcm_file_offset=0;
+      _link->pcm_start=_link->pcm_end=0;
+      _link->end_offset=_link->data_offset;
+      /*Tell the caller we've got a buffered page for them.*/
+      return 1;
+    }
+    /*Ignore pages from other streams (not strictly necessary, because of the
+       checks in ogg_stream_pagein(), but saves some work).*/
+    if(serialno!=(ogg_uint32_t)ogg_page_serialno(_og))continue;
+    ogg_stream_pagein(&_of->os,_og);
+    /*Bitrate tracking: add the header's bytes here.
+      The body bytes are counted when we consume the packets.*/
+    _of->bytes_tracked+=_og->header_len;
+    /*Count the durations of all packets in the page.*/
+    do total_duration=op_collect_audio_packets(_of,durations);
+    /*Ignore holes.*/
+    while(OP_UNLIKELY(total_duration<0));
+    op_count=_of->op_count;
+  }
+  while(op_count<=0);
+  /*We found the first page with a completed audio data packet: actually look
+     at the granule position.
+    RFC 3533 says, "A special value of -1 (in two's complement) indicates that
+     no packets finish on this page," which does not say that a granule
+     position that is NOT -1 indicates that some packets DO finish on that page
+     (even though this was the intention, libogg itself violated this intention
+     for years before we fixed it).
+    The Ogg Opus specification only imposes its start-time requirements
+     on the granule position of the first page with completed packets,
+     so we ignore any set granule positions until then.*/
+  cur_page_gp=_of->op[op_count-1].granulepos;
+  /*But getting a packet without a valid granule position on the page is not
+     okay.*/
+  if(cur_page_gp==-1)return OP_EBADTIMESTAMP;
+  cur_page_eos=_of->op[op_count-1].e_o_s;
+  if(OP_LIKELY(!cur_page_eos)){
+    /*The EOS flag wasn't set.
+      Work backwards from the provided granule position to get the starting PCM
+       offset.*/
+    if(OP_UNLIKELY(op_granpos_add(&pcm_start,cur_page_gp,-total_duration)<0)){
+      /*The starting granule position MUST not be smaller than the amount of
+         audio on the first page with completed packets.*/
+      return OP_EBADTIMESTAMP;
+    }
+  }
+  else{
+    /*The first page with completed packets was also the last.*/
+    if(OP_LIKELY(op_granpos_add(&pcm_start,cur_page_gp,-total_duration)<0)){
+      /*If there's less audio on the page than indicated by the granule
+         position, then we're doing end-trimming, and the starting PCM offset
+         is zero by spec mandate.*/
+      pcm_start=0;
+      /*However, the end-trimming MUST not ask us to trim more samples than
+         exist after applying the pre-skip.*/
+      if(OP_UNLIKELY(op_granpos_cmp(cur_page_gp,_link->head.pre_skip)<0)){
+        return OP_EBADTIMESTAMP;
+      }
+    }
+  }
+  /*Timestamp the individual packets.*/
+  prev_packet_gp=pcm_start;
+  for(pi=0;pi<op_count;pi++){
+    if(cur_page_eos){
+      ogg_int64_t diff;
+      OP_ALWAYS_TRUE(!op_granpos_diff(&diff,cur_page_gp,prev_packet_gp));
+      diff=durations[pi]-diff;
+      /*If we have samples to trim...*/
+      if(diff>0){
+        /*If we trimmed the entire packet, stop (the spec says encoders
+           shouldn't do this, but we support it anyway).*/
+        if(OP_UNLIKELY(diff>durations[pi]))break;
+        _of->op[pi].granulepos=prev_packet_gp=cur_page_gp;
+        /*Move the EOS flag to this packet, if necessary, so we'll trim the
+           samples.*/
+        _of->op[pi].e_o_s=1;
+        continue;
+      }
+    }
+    /*Update the granule position as normal.*/
+    OP_ALWAYS_TRUE(!op_granpos_add(&_of->op[pi].granulepos,
+     prev_packet_gp,durations[pi]));
+    prev_packet_gp=_of->op[pi].granulepos;
+  }
+  /*Update the packet count after end-trimming.*/
+  _of->op_count=pi;
+  _of->cur_discard_count=_link->head.pre_skip;
+  _link->pcm_file_offset=0;
+  _of->prev_packet_gp=_link->pcm_start=pcm_start;
+  _of->prev_page_offset=page_offset;
+  return 0;
+}
+
+/*Starting from current cursor position, get the final PCM offset of the
+   previous page.
+  This also validates the duration of the link, which, while not strictly
+   required by the spec, we need to ensure duration calculations don't
+   overflow.
+  This is only done for seekable sources.
+  We must validate that op_find_initial_pcm_offset() succeeded for this link
+   before calling this function, otherwise it will scan the entire stream
+   backwards until it reaches the start, and then fail.*/
+static int op_find_final_pcm_offset(OggOpusFile *_of,
+ const ogg_uint32_t *_serialnos,int _nserialnos,OggOpusLink *_link,
+ opus_int64 _offset,ogg_uint32_t _end_serialno,ogg_int64_t _end_gp,
+ ogg_int64_t *_total_duration){
+  ogg_int64_t  total_duration;
+  ogg_int64_t  duration;
+  ogg_uint32_t cur_serialno;
+  /*For the time being, fetch end PCM offset the simple way.*/
+  cur_serialno=_link->serialno;
+  if(_end_serialno!=cur_serialno||_end_gp==-1){
+    _offset=op_get_last_page(_of,&_end_gp,_offset,
+     cur_serialno,_serialnos,_nserialnos);
+    if(OP_UNLIKELY(_offset<0))return (int)_offset;
+  }
+  /*At worst we should have found the first page with completed packets.*/
+  if(OP_UNLIKELY(_offset<_link->data_offset))return OP_EBADLINK;
+  /*This implementation requires that the difference between the first and last
+     granule positions in each link be representable in a signed, 64-bit
+     number, and that each link also have at least as many samples as the
+     pre-skip requires.*/
+  if(OP_UNLIKELY(op_granpos_diff(&duration,_end_gp,_link->pcm_start)<0)
+   ||OP_UNLIKELY(duration<_link->head.pre_skip)){
+    return OP_EBADTIMESTAMP;
+  }
+  /*We also require that the total duration be representable in a signed,
+     64-bit number.*/
+  duration-=_link->head.pre_skip;
+  total_duration=*_total_duration;
+  if(OP_UNLIKELY(OP_INT64_MAX-duration<total_duration))return OP_EBADTIMESTAMP;
+  *_total_duration=total_duration+duration;
+  _link->pcm_end=_end_gp;
+  _link->end_offset=_offset;
+  return 0;
+}
+
+/*Rescale the number _x from the range [0,_from] to [0,_to].
+  _from and _to must be positive.*/
+static opus_int64 op_rescale64(opus_int64 _x,opus_int64 _from,opus_int64 _to){
+  opus_int64 frac;
+  opus_int64 ret;
+  int        i;
+  if(_x>=_from)return _to;
+  if(_x<=0)return 0;
+  frac=0;
+  for(i=0;i<63;i++){
+    frac<<=1;
+    OP_ASSERT(_x<=_from);
+    if(_x>=_from>>1){
+      _x-=_from-_x;
+      frac|=1;
+    }
+    else _x<<=1;
+  }
+  ret=0;
+  for(i=0;i<63;i++){
+    if(frac&1)ret=(ret&_to&1)+(ret>>1)+(_to>>1);
+    else ret>>=1;
+    frac>>=1;
+  }
+  return ret;
+}
+
+/*The minimum granule position spacing allowed for making predictions.
+  This corresponds to about 1 second of audio at 48 kHz for both Opus and
+   Vorbis, or one keyframe interval in Theora with the default keyframe spacing
+   of 256.*/
+#define OP_GP_SPACING_MIN (48000)
+
+/*Try to estimate the location of the next link using the current seek
+   records, assuming the initial granule position of any streams we've found is
+   0.*/
+static opus_int64 op_predict_link_start(const OpusSeekRecord *_sr,int _nsr,
+ opus_int64 _searched,opus_int64 _end_searched,opus_int32 _bias){
+  opus_int64 bisect;
+  int        sri;
+  int        srj;
+  /*Require that we be at least OP_CHUNK_SIZE from the end.
+    We don't require that we be at least OP_CHUNK_SIZE from the beginning,
+     because if we are we'll just scan forward without seeking.*/
+  _end_searched-=OP_CHUNK_SIZE;
+  if(_searched>=_end_searched)return -1;
+  bisect=_end_searched;
+  for(sri=0;sri<_nsr;sri++){
+    ogg_int64_t  gp1;
+    ogg_int64_t  gp2_min;
+    ogg_uint32_t serialno1;
+    opus_int64   offset1;
+    /*If the granule position is negative, either it's invalid or we'd cause
+       overflow.*/
+    gp1=_sr[sri].gp;
+    if(gp1<0)continue;
+    /*We require some minimum distance between granule positions to make an
+       estimate.
+      We don't actually know what granule position scheme is being used,
+       because we have no idea what kind of stream these came from.
+      Therefore we require a minimum spacing between them, with the
+       expectation that while bitrates and granule position increments might
+       vary locally in quite complex ways, they are globally smooth.*/
+    if(OP_UNLIKELY(op_granpos_add(&gp2_min,gp1,OP_GP_SPACING_MIN)<0)){
+      /*No granule position would satisfy us.*/
+      continue;
+    }
+    offset1=_sr[sri].offset;
+    serialno1=_sr[sri].serialno;
+    for(srj=sri;srj-->0;){
+      ogg_int64_t gp2;
+      opus_int64  offset2;
+      opus_int64  num;
+      ogg_int64_t den;
+      ogg_int64_t ipart;
+      gp2=_sr[srj].gp;
+      if(gp2<gp2_min)continue;
+      /*Oh, and also make sure these came from the same stream.*/
+      if(_sr[srj].serialno!=serialno1)continue;
+      offset2=_sr[srj].offset;
+      /*For once, we can subtract with impunity.*/
+      den=gp2-gp1;
+      ipart=gp2/den;
+      num=offset2-offset1;
+      OP_ASSERT(num>0);
+      if(ipart>0&&(offset2-_searched)/ipart<num)continue;
+      offset2-=ipart*num;
+      gp2-=ipart*den;
+      offset2-=op_rescale64(gp2,den,num)-_bias;
+      if(offset2<_searched)continue;
+      bisect=OP_MIN(bisect,offset2);
+      break;
+    }
+  }
+  return bisect>=_end_searched?-1:bisect;
+}
+
+/*Finds each bitstream link, one at a time, using a bisection search.
+  This has to begin by knowing the offset of the first link's initial page.*/
+static int op_bisect_forward_serialno(OggOpusFile *_of,
+ opus_int64 _searched,OpusSeekRecord *_sr,int _csr,
+ ogg_uint32_t **_serialnos,int *_nserialnos,int *_cserialnos){
+  ogg_page      og;
+  OggOpusLink  *links;
+  int           nlinks;
+  int           clinks;
+  ogg_uint32_t *serialnos;
+  int           nserialnos;
+  ogg_int64_t   total_duration;
+  int           nsr;
+  int           ret;
+  links=_of->links;
+  nlinks=clinks=_of->nlinks;
+  total_duration=0;
+  /*We start with one seek record, for the last page in the file.
+    We build up a list of records for places we seek to during link
+     enumeration.
+    This list is kept sorted in reverse order.
+    We only care about seek locations that were _not_ in the current link,
+     therefore we can add them one at a time to the end of the list as we
+     improve the lower bound on the location where the next link starts.*/
+  nsr=1;
+  for(;;){
+    opus_int64  end_searched;
+    opus_int64  bisect;
+    opus_int64  next;
+    opus_int64  last;
+    ogg_int64_t end_offset;
+    ogg_int64_t end_gp;
+    int         sri;
+    serialnos=*_serialnos;
+    nserialnos=*_nserialnos;
+    if(OP_UNLIKELY(nlinks>=clinks)){
+      if(OP_UNLIKELY(clinks>INT_MAX-1>>1))return OP_EFAULT;
+      clinks=2*clinks+1;
+      OP_ASSERT(nlinks<clinks);
+      links=(OggOpusLink *)_ogg_realloc(links,sizeof(*links)*clinks);
+      if(OP_UNLIKELY(links==NULL))return OP_EFAULT;
+      _of->links=links;
+    }
+    /*Invariants:
+      We have the headers and serial numbers for the link beginning at 'begin'.
+      We have the offset and granule position of the last page in the file
+       (potentially not a page we care about).*/
+    /*Scan the seek records we already have to save us some bisection.*/
+    for(sri=0;sri<nsr;sri++){
+      if(op_lookup_serialno(_sr[sri].serialno,serialnos,nserialnos))break;
+    }
+    /*Is the last page in our current list of serial numbers?*/
+    if(sri<=0)break;
+    /*Last page wasn't found.
+      We have at least one more link.*/
+    last=-1;
+    end_searched=_sr[sri-1].search_start;
+    next=_sr[sri-1].offset;
+    end_gp=-1;
+    if(sri<nsr){
+      _searched=_sr[sri].offset+_sr[sri].size;
+      if(_sr[sri].serialno==links[nlinks-1].serialno){
+        end_gp=_sr[sri].gp;
+        end_offset=_sr[sri].offset;
+      }
+    }
+    nsr=sri;
+    bisect=-1;
+    /*If we've already found the end of at least one link, try to pick the
+       first bisection point at twice the average link size.
+      This is a good choice for files with lots of links that are all about the
+       same size.*/
+    if(nlinks>1){
+      opus_int64 last_offset;
+      opus_int64 avg_link_size;
+      opus_int64 upper_limit;
+      last_offset=links[nlinks-1].offset;
+      avg_link_size=last_offset/(nlinks-1);
+      upper_limit=end_searched-OP_CHUNK_SIZE-avg_link_size;
+      if(OP_LIKELY(last_offset>_searched-avg_link_size)
+       &&OP_LIKELY(last_offset<upper_limit)){
+        bisect=last_offset+avg_link_size;
+        if(OP_LIKELY(bisect<upper_limit))bisect+=avg_link_size;
+      }
+    }
+    /*We guard against garbage separating the last and first pages of two
+       links below.*/
+    while(_searched<end_searched){
+      opus_int32 next_bias;
+      /*If we don't have a better estimate, use simple bisection.*/
+      if(bisect==-1)bisect=_searched+(end_searched-_searched>>1);
+      /*If we're within OP_CHUNK_SIZE of the start, scan forward.*/
+      if(bisect-_searched<OP_CHUNK_SIZE)bisect=_searched;
+      /*Otherwise we're skipping data.
+        Forget the end page, if we saw one, as we might miss a later one.*/
+      else end_gp=-1;
+      ret=op_seek_helper(_of,bisect);
+      if(OP_UNLIKELY(ret<0))return ret;
+      last=op_get_next_page(_of,&og,_sr[nsr-1].offset);
+      if(OP_UNLIKELY(last<OP_FALSE))return (int)last;
+      next_bias=0;
+      if(last==OP_FALSE)end_searched=bisect;
+      else{
+        ogg_uint32_t serialno;
+        ogg_int64_t  gp;
+        serialno=ogg_page_serialno(&og);
+        gp=ogg_page_granulepos(&og);
+        if(!op_lookup_serialno(serialno,serialnos,nserialnos)){
+          end_searched=bisect;
+          next=last;
+          /*In reality we should always have enough room, but be paranoid.*/
+          if(OP_LIKELY(nsr<_csr)){
+            _sr[nsr].search_start=bisect;
+            _sr[nsr].offset=last;
+            OP_ASSERT(_of->offset-last>=0);
+            OP_ASSERT(_of->offset-last<=OP_PAGE_SIZE_MAX);
+            _sr[nsr].size=(opus_int32)(_of->offset-last);
+            _sr[nsr].serialno=serialno;
+            _sr[nsr].gp=gp;
+            nsr++;
+          }
+        }
+        else{
+          _searched=_of->offset;
+          next_bias=OP_CHUNK_SIZE;
+          if(serialno==links[nlinks-1].serialno){
+            /*This page was from the stream we want, remember it.
+              If it's the last such page in the link, we won't have to go back
+               looking for it later.*/
+            end_gp=gp;
+            end_offset=last;
+          }
+        }
+      }
+      bisect=op_predict_link_start(_sr,nsr,_searched,end_searched,next_bias);
+    }
+    /*Bisection point found.
+      Get the final granule position of the previous link, assuming
+       op_find_initial_pcm_offset() didn't already determine the link was
+       empty.*/
+    if(OP_LIKELY(links[nlinks-1].pcm_end==-1)){
+      if(end_gp==-1){
+        /*If we don't know where the end page is, we'll have to seek back and
+           look for it, starting from the end of the link.*/
+        end_offset=next;
+        /*Also forget the last page we read.
+          It won't be available after the seek.*/
+        last=-1;
+      }
+      ret=op_find_final_pcm_offset(_of,serialnos,nserialnos,
+       links+nlinks-1,end_offset,links[nlinks-1].serialno,end_gp,
+       &total_duration);
+      if(OP_UNLIKELY(ret<0))return ret;
+    }
+    if(last!=next){
+      /*The last page we read was not the first page the next link.
+        Move the cursor position to the offset of that first page.
+        This only performs an actual seek if the first page of the next link
+         does not start at the end of the last page from the current Opus
+         stream with a valid granule position.*/
+      ret=op_seek_helper(_of,next);
+      if(OP_UNLIKELY(ret<0))return ret;
+    }
+    ret=op_fetch_headers(_of,&links[nlinks].head,&links[nlinks].tags,
+     _serialnos,_nserialnos,_cserialnos,last!=next?NULL:&og);
+    if(OP_UNLIKELY(ret<0))return ret;
+    links[nlinks].offset=next;
+    links[nlinks].data_offset=_of->offset;
+    links[nlinks].serialno=_of->os.serialno;
+    links[nlinks].pcm_end=-1;
+    /*This might consume a page from the next link, however the next bisection
+       always starts with a seek.*/
+    ret=op_find_initial_pcm_offset(_of,links+nlinks,NULL);
+    if(OP_UNLIKELY(ret<0))return ret;
+    links[nlinks].pcm_file_offset=total_duration;
+    _searched=_of->offset;
+    /*Mark the current link count so it can be cleaned up on error.*/
+    _of->nlinks=++nlinks;
+  }
+  /*Last page is in the starting serialno list, so we've reached the last link.
+    Now find the last granule position for it (if we didn't the first time we
+     looked at the end of the stream, and if op_find_initial_pcm_offset()
+     didn't already determine the link was empty).*/
+  if(OP_LIKELY(links[nlinks-1].pcm_end==-1)){
+    ret=op_find_final_pcm_offset(_of,serialnos,nserialnos,
+     links+nlinks-1,_sr[0].offset,_sr[0].serialno,_sr[0].gp,&total_duration);
+    if(OP_UNLIKELY(ret<0))return ret;
+  }
+  /*Trim back the links array if necessary.*/
+  links=(OggOpusLink *)_ogg_realloc(links,sizeof(*links)*nlinks);
+  if(OP_LIKELY(links!=NULL))_of->links=links;
+  /*We also don't need these anymore.*/
+  _ogg_free(*_serialnos);
+  *_serialnos=NULL;
+  *_cserialnos=*_nserialnos=0;
+  return 0;
+}
+
+static void op_update_gain(OggOpusFile *_of){
+  OpusHead   *head;
+  opus_int32  gain_q8;
+  int         li;
+  /*If decode isn't ready, then we'll apply the gain when we initialize the
+     decoder.*/
+  if(_of->ready_state<OP_INITSET)return;
+  gain_q8=_of->gain_offset_q8;
+  li=_of->seekable?_of->cur_link:0;
+  head=&_of->links[li].head;
+  /*We don't have to worry about overflow here because the header gain and
+     track gain must lie in the range [-32768,32767], and the user-supplied
+     offset has been pre-clamped to [-98302,98303].*/
+  switch(_of->gain_type){
+    case OP_ALBUM_GAIN:{
+      int album_gain_q8;
+      album_gain_q8=0;
+      opus_tags_get_album_gain(&_of->links[li].tags,&album_gain_q8);
+      gain_q8+=album_gain_q8;
+      gain_q8+=head->output_gain;
+    }break;
+    case OP_TRACK_GAIN:{
+      int track_gain_q8;
+      track_gain_q8=0;
+      opus_tags_get_track_gain(&_of->links[li].tags,&track_gain_q8);
+      gain_q8+=track_gain_q8;
+      gain_q8+=head->output_gain;
+    }break;
+    case OP_HEADER_GAIN:gain_q8+=head->output_gain;break;
+    case OP_ABSOLUTE_GAIN:break;
+    default:OP_ASSERT(0);
+  }
+  gain_q8=OP_CLAMP(-32768,gain_q8,32767);
+  OP_ASSERT(_of->od!=NULL);
+#if defined(OPUS_SET_GAIN)
+  opus_multistream_decoder_ctl(_of->od,OPUS_SET_GAIN(gain_q8));
+#else
+/*A fallback that works with both float and fixed-point is a bunch of work,
+   so just force people to use a sufficiently new version.
+  This is deployed well enough at this point that this shouldn't be a burden.*/
+# error "libopus 1.0.1 or later required"
+#endif
+}
+
+static int op_make_decode_ready(OggOpusFile *_of){
+  const OpusHead *head;
+  int             li;
+  int             stream_count;
+  int             coupled_count;
+  int             channel_count;
+  if(_of->ready_state>OP_STREAMSET)return 0;
+  if(OP_UNLIKELY(_of->ready_state<OP_STREAMSET))return OP_EFAULT;
+  li=_of->seekable?_of->cur_link:0;
+  head=&_of->links[li].head;
+  stream_count=head->stream_count;
+  coupled_count=head->coupled_count;
+  channel_count=head->channel_count;
+  /*Check to see if the current decoder is compatible with the current link.*/
+  if(_of->od!=NULL&&_of->od_stream_count==stream_count
+   &&_of->od_coupled_count==coupled_count&&_of->od_channel_count==channel_count
+   &&memcmp(_of->od_mapping,head->mapping,
+   sizeof(*head->mapping)*channel_count)==0){
+    opus_multistream_decoder_ctl(_of->od,OPUS_RESET_STATE);
+  }
+  else{
+    int err;
+    opus_multistream_decoder_destroy(_of->od);
+    _of->od=opus_multistream_decoder_create(48000,channel_count,
+     stream_count,coupled_count,head->mapping,&err);
+    if(_of->od==NULL)return OP_EFAULT;
+    _of->od_stream_count=stream_count;
+    _of->od_coupled_count=coupled_count;
+    _of->od_channel_count=channel_count;
+    memcpy(_of->od_mapping,head->mapping,sizeof(*head->mapping)*channel_count);
+  }
+  _of->ready_state=OP_INITSET;
+  _of->bytes_tracked=0;
+  _of->samples_tracked=0;
+#if !defined(OP_FIXED_POINT)
+  _of->state_channel_count=0;
+  /*Use the serial number for the PRNG seed to get repeatable output for
+     straight play-throughs.*/
+  _of->dither_seed=_of->links[li].serialno;
+#endif
+  op_update_gain(_of);
+  return 0;
+}
+
+static int op_open_seekable2_impl(OggOpusFile *_of){
+  /*64 seek records should be enough for anybody.
+    Actually, with a bisection search in a 63-bit range down to OP_CHUNK_SIZE
+     granularity, much more than enough.*/
+  OpusSeekRecord sr[64];
+  opus_int64     data_offset;
+  int            ret;
+  /*We can seek, so set out learning all about this file.*/
+  (*_of->callbacks.seek)(_of->stream,0,SEEK_END);
+  _of->offset=_of->end=(*_of->callbacks.tell)(_of->stream);
+  if(OP_UNLIKELY(_of->end<0))return OP_EREAD;
+  data_offset=_of->links[0].data_offset;
+  if(OP_UNLIKELY(_of->end<data_offset))return OP_EBADLINK;
+  /*Get the offset of the last page of the physical bitstream, or, if we're
+     lucky, the last Opus page of the first link, as most Ogg Opus files will
+     contain a single logical bitstream.*/
+  ret=op_get_prev_page_serial(_of,sr,_of->end,
+   _of->links[0].serialno,_of->serialnos,_of->nserialnos);
+  if(OP_UNLIKELY(ret<0))return ret;
+  /*If there's any trailing junk, forget about it.*/
+  _of->end=sr[0].offset+sr[0].size;
+  if(OP_UNLIKELY(_of->end<data_offset))return OP_EBADLINK;
+  /*Now enumerate the bitstream structure.*/
+  return op_bisect_forward_serialno(_of,data_offset,sr,sizeof(sr)/sizeof(*sr),
+   &_of->serialnos,&_of->nserialnos,&_of->cserialnos);
+}
+
+static int op_open_seekable2(OggOpusFile *_of){
+  ogg_sync_state    oy_start;
+  ogg_stream_state  os_start;
+  ogg_packet       *op_start;
+  opus_int64        prev_page_offset;
+  opus_int64        start_offset;
+  int               start_op_count;
+  int               ret;
+  /*We're partially open and have a first link header state in storage in _of.
+    Save off that stream state so we can come back to it.
+    It would be simpler to just dump all this state and seek back to
+     links[0].data_offset when we're done.
+    But we do the extra work to allow us to seek back to _exactly_ the same
+     stream position we're at now.
+    This allows, e.g., the HTTP backend to continue reading from the original
+     connection (if it's still available), instead of opening a new one.
+    This means we can open and start playing a normal Opus file with a single
+     link and reasonable packet sizes using only two HTTP requests.*/
+  start_op_count=_of->op_count;
+  /*This is a bit too large to put on the stack unconditionally.*/
+  op_start=(ogg_packet *)_ogg_malloc(sizeof(*op_start)*start_op_count);
+  if(op_start==NULL)return OP_EFAULT;
+  *&oy_start=_of->oy;
+  *&os_start=_of->os;
+  prev_page_offset=_of->prev_page_offset;
+  start_offset=_of->offset;
+  memcpy(op_start,_of->op,sizeof(*op_start)*start_op_count);
+  OP_ASSERT((*_of->callbacks.tell)(_of->stream)==op_position(_of));
+  ogg_sync_init(&_of->oy);
+  ogg_stream_init(&_of->os,-1);
+  ret=op_open_seekable2_impl(_of);
+  /*Restore the old stream state.*/
+  ogg_stream_clear(&_of->os);
+  ogg_sync_clear(&_of->oy);
+  *&_of->oy=*&oy_start;
+  *&_of->os=*&os_start;
+  _of->offset=start_offset;
+  _of->op_count=start_op_count;
+  memcpy(_of->op,op_start,sizeof(*_of->op)*start_op_count);
+  _ogg_free(op_start);
+  _of->prev_packet_gp=_of->links[0].pcm_start;
+  _of->prev_page_offset=prev_page_offset;
+  _of->cur_discard_count=_of->links[0].head.pre_skip;
+  if(OP_UNLIKELY(ret<0))return ret;
+  /*And restore the position indicator.*/
+  ret=(*_of->callbacks.seek)(_of->stream,op_position(_of),SEEK_SET);
+  return OP_UNLIKELY(ret<0)?OP_EREAD:0;
+}
+
+/*Clear out the current logical bitstream decoder.*/
+static void op_decode_clear(OggOpusFile *_of){
+  /*We don't actually free the decoder.
+    We might be able to re-use it for the next link.*/
+  _of->op_count=0;
+  _of->od_buffer_size=0;
+  _of->prev_packet_gp=-1;
+  _of->prev_page_offset=-1;
+  if(!_of->seekable){
+    OP_ASSERT(_of->ready_state>=OP_INITSET);
+    opus_tags_clear(&_of->links[0].tags);
+  }
+  _of->ready_state=OP_OPENED;
+}
+
+static void op_clear(OggOpusFile *_of){
+  OggOpusLink *links;
+  _ogg_free(_of->od_buffer);
+  if(_of->od!=NULL)opus_multistream_decoder_destroy(_of->od);
+  links=_of->links;
+  if(!_of->seekable){
+    if(_of->ready_state>OP_OPENED||_of->ready_state==OP_PARTOPEN){
+      opus_tags_clear(&links[0].tags);
+    }
+  }
+  else if(OP_LIKELY(links!=NULL)){
+    int nlinks;
+    int link;
+    nlinks=_of->nlinks;
+    for(link=0;link<nlinks;link++)opus_tags_clear(&links[link].tags);
+  }
+  _ogg_free(links);
+  _ogg_free(_of->serialnos);
+  ogg_stream_clear(&_of->os);
+  ogg_sync_clear(&_of->oy);
+  if(_of->callbacks.close!=NULL)(*_of->callbacks.close)(_of->stream);
+}
+
+static int op_open1(OggOpusFile *_of,
+ void *_stream,const OpusFileCallbacks *_cb,
+ const unsigned char *_initial_data,size_t _initial_bytes){
+  ogg_page  og;
+  ogg_page *pog;
+  int       seekable;
+  int       ret;
+  memset(_of,0,sizeof(*_of));
+  if(OP_UNLIKELY(_initial_bytes>(size_t)LONG_MAX))return OP_EFAULT;
+  _of->end=-1;
+  _of->stream=_stream;
+  *&_of->callbacks=*_cb;
+  /*At a minimum, we need to be able to read data.*/
+  if(OP_UNLIKELY(_of->callbacks.read==NULL))return OP_EREAD;
+  /*Initialize the framing state.*/
+  ogg_sync_init(&_of->oy);
+  /*Perhaps some data was previously read into a buffer for testing against
+     other stream types.
+    Allow initialization from this previously read data (especially as we may
+     be reading from a non-seekable stream).
+    This requires copying it into a buffer allocated by ogg_sync_buffer() and
+     doesn't support seeking, so this is not a good mechanism to use for
+     decoding entire files from RAM.*/
+  if(_initial_bytes>0){
+    char *buffer;
+    buffer=ogg_sync_buffer(&_of->oy,(long)_initial_bytes);
+    memcpy(buffer,_initial_data,_initial_bytes*sizeof(*buffer));
+    ogg_sync_wrote(&_of->oy,(long)_initial_bytes);
+  }
+  /*Can we seek?
+    Stevens suggests the seek test is portable.*/
+  seekable=_cb->seek!=NULL&&(*_cb->seek)(_stream,0,SEEK_CUR)!=-1;
+  /*If seek is implemented, tell must also be implemented.*/
+  if(seekable){
+    opus_int64 pos;
+    if(OP_UNLIKELY(_of->callbacks.tell==NULL))return OP_EINVAL;
+    pos=(*_of->callbacks.tell)(_of->stream);
+    /*If the current position is not equal to the initial bytes consumed,
+       absolute seeking will not work.*/
+    if(OP_UNLIKELY(pos!=(opus_int64)_initial_bytes))return OP_EINVAL;
+  }
+  _of->seekable=seekable;
+  /*Don't seek yet.
+    Set up a 'single' (current) logical bitstream entry for partial open.*/
+  _of->links=(OggOpusLink *)_ogg_malloc(sizeof(*_of->links));
+  /*The serialno gets filled in later by op_fetch_headers().*/
+  ogg_stream_init(&_of->os,-1);
+  pog=NULL;
+  for(;;){
+    /*Fetch all BOS pages, store the Opus header and all seen serial numbers,
+      and load subsequent Opus setup headers.*/
+    ret=op_fetch_headers(_of,&_of->links[0].head,&_of->links[0].tags,
+     &_of->serialnos,&_of->nserialnos,&_of->cserialnos,pog);
+    if(OP_UNLIKELY(ret<0))break;
+    _of->nlinks=1;
+    _of->links[0].offset=0;
+    _of->links[0].data_offset=_of->offset;
+    _of->links[0].pcm_end=-1;
+    _of->links[0].serialno=_of->os.serialno;
+    /*Fetch the initial PCM offset.*/
+    ret=op_find_initial_pcm_offset(_of,_of->links,&og);
+    if(seekable||OP_LIKELY(ret<=0))break;
+    /*This link was empty, but we already have the BOS page for the next one in
+       og.
+      We can't seek, so start processing the next link right now.*/
+    opus_tags_clear(&_of->links[0].tags);
+    _of->nlinks=0;
+    if(!seekable)_of->cur_link++;
+    pog=&og;
+  }
+  if(OP_LIKELY(ret>=0))_of->ready_state=OP_PARTOPEN;
+  return ret;
+}
+
+static int op_open2(OggOpusFile *_of){
+  int ret;
+  OP_ASSERT(_of->ready_state==OP_PARTOPEN);
+  if(_of->seekable){
+    _of->ready_state=OP_OPENED;
+    ret=op_open_seekable2(_of);
+  }
+  else ret=0;
+  if(OP_LIKELY(ret>=0)){
+    /*We have buffered packets from op_find_initial_pcm_offset().
+      Move to OP_INITSET so we can use them.*/
+    _of->ready_state=OP_STREAMSET;
+    ret=op_make_decode_ready(_of);
+    if(OP_LIKELY(ret>=0))return 0;
+  }
+  /*Don't auto-close the stream on failure.*/
+  _of->callbacks.close=NULL;
+  op_clear(_of);
+  return ret;
+}
+
+OggOpusFile *op_test_callbacks(void *_stream,const OpusFileCallbacks *_cb,
+ const unsigned char *_initial_data,size_t _initial_bytes,int *_error){
+  OggOpusFile *of;
+  int          ret;
+  of=(OggOpusFile *)_ogg_malloc(sizeof(*of));
+  ret=OP_EFAULT;
+  if(OP_LIKELY(of!=NULL)){
+    ret=op_open1(of,_stream,_cb,_initial_data,_initial_bytes);
+    if(OP_LIKELY(ret>=0)){
+      if(_error!=NULL)*_error=0;
+      return of;
+    }
+    /*Don't auto-close the stream on failure.*/
+    of->callbacks.close=NULL;
+    op_clear(of);
+    _ogg_free(of);
+  }
+  if(_error!=NULL)*_error=ret;
+  return NULL;
+}
+
+OggOpusFile *op_open_callbacks(void *_stream,const OpusFileCallbacks *_cb,
+ const unsigned char *_initial_data,size_t _initial_bytes,int *_error){
+  OggOpusFile *of;
+  of=op_test_callbacks(_stream,_cb,_initial_data,_initial_bytes,_error);
+  if(OP_LIKELY(of!=NULL)){
+    int ret;
+    ret=op_open2(of);
+    if(OP_LIKELY(ret>=0))return of;
+    if(_error!=NULL)*_error=ret;
+    _ogg_free(of);
+  }
+  return NULL;
+}
+
+/*Convenience routine to clean up from failure for the open functions that
+   create their own streams.*/
+static OggOpusFile *op_open_close_on_failure(void *_stream,
+ const OpusFileCallbacks *_cb,int *_error){
+  OggOpusFile *of;
+  if(OP_UNLIKELY(_stream==NULL)){
+    if(_error!=NULL)*_error=OP_EFAULT;
+    return NULL;
+  }
+  of=op_open_callbacks(_stream,_cb,NULL,0,_error);
+  if(OP_UNLIKELY(of==NULL))(*_cb->close)(_stream);
+  return of;
+}
+
+OggOpusFile *op_open_file(const char *_path,int *_error){
+  OpusFileCallbacks cb;
+  return op_open_close_on_failure(op_fopen(&cb,_path,"rb"),&cb,_error);
+}
+
+OggOpusFile *op_open_memory(const unsigned char *_data,size_t _size,
+ int *_error){
+  OpusFileCallbacks cb;
+  return op_open_close_on_failure(op_mem_stream_create(&cb,_data,_size),&cb,
+   _error);
+}
+
+/*Convenience routine to clean up from failure for the open functions that
+   create their own streams.*/
+static OggOpusFile *op_test_close_on_failure(void *_stream,
+ const OpusFileCallbacks *_cb,int *_error){
+  OggOpusFile *of;
+  if(OP_UNLIKELY(_stream==NULL)){
+    if(_error!=NULL)*_error=OP_EFAULT;
+    return NULL;
+  }
+  of=op_test_callbacks(_stream,_cb,NULL,0,_error);
+  if(OP_UNLIKELY(of==NULL))(*_cb->close)(_stream);
+  return of;
+}
+
+OggOpusFile *op_test_file(const char *_path,int *_error){
+  OpusFileCallbacks cb;
+  return op_test_close_on_failure(op_fopen(&cb,_path,"rb"),&cb,_error);
+}
+
+OggOpusFile *op_test_memory(const unsigned char *_data,size_t _size,
+ int *_error){
+  OpusFileCallbacks cb;
+  return op_test_close_on_failure(op_mem_stream_create(&cb,_data,_size),&cb,
+   _error);
+}
+
+int op_test_open(OggOpusFile *_of){
+  int ret;
+  if(OP_UNLIKELY(_of->ready_state!=OP_PARTOPEN))return OP_EINVAL;
+  ret=op_open2(_of);
+  /*op_open2() will clear this structure on failure.
+    Reset its contents to prevent double-frees in op_free().*/
+  if(OP_UNLIKELY(ret<0))memset(_of,0,sizeof(*_of));
+  return ret;
+}
+
+void op_free(OggOpusFile *_of){
+  if(OP_LIKELY(_of!=NULL)){
+    op_clear(_of);
+    _ogg_free(_of);
+  }
+}
+
+int op_seekable(const OggOpusFile *_of){
+  return _of->seekable;
+}
+
+int op_link_count(const OggOpusFile *_of){
+  return _of->nlinks;
+}
+
+opus_uint32 op_serialno(const OggOpusFile *_of,int _li){
+  if(OP_UNLIKELY(_li>=_of->nlinks))_li=_of->nlinks-1;
+  if(!_of->seekable)_li=0;
+  return _of->links[_li<0?_of->cur_link:_li].serialno;
+}
+
+int op_channel_count(const OggOpusFile *_of,int _li){
+  return op_head(_of,_li)->channel_count;
+}
+
+opus_int64 op_raw_total(const OggOpusFile *_of,int _li){
+  if(OP_UNLIKELY(_of->ready_state<OP_OPENED)
+   ||OP_UNLIKELY(!_of->seekable)
+   ||OP_UNLIKELY(_li>=_of->nlinks)){
+    return OP_EINVAL;
+  }
+  if(_li<0)return _of->end;
+  return (_li+1>=_of->nlinks?_of->end:_of->links[_li+1].offset)
+   -(_li>0?_of->links[_li].offset:0);
+}
+
+ogg_int64_t op_pcm_total(const OggOpusFile *_of,int _li){
+  OggOpusLink *links;
+  ogg_int64_t  pcm_total;
+  ogg_int64_t  diff;
+  int          nlinks;
+  nlinks=_of->nlinks;
+  if(OP_UNLIKELY(_of->ready_state<OP_OPENED)
+   ||OP_UNLIKELY(!_of->seekable)
+   ||OP_UNLIKELY(_li>=nlinks)){
+    return OP_EINVAL;
+  }
+  links=_of->links;
+  /*We verify that the granule position differences are larger than the
+     pre-skip and that the total duration does not overflow during link
+     enumeration, so we don't have to check here.*/
+  pcm_total=0;
+  if(_li<0){
+    pcm_total=links[nlinks-1].pcm_file_offset;
+    _li=nlinks-1;
+  }
+  OP_ALWAYS_TRUE(!op_granpos_diff(&diff,
+   links[_li].pcm_end,links[_li].pcm_start));
+  return pcm_total+diff-links[_li].head.pre_skip;
+}
+
+const OpusHead *op_head(const OggOpusFile *_of,int _li){
+  if(OP_UNLIKELY(_li>=_of->nlinks))_li=_of->nlinks-1;
+  if(!_of->seekable)_li=0;
+  return &_of->links[_li<0?_of->cur_link:_li].head;
+}
+
+const OpusTags *op_tags(const OggOpusFile *_of,int _li){
+  if(OP_UNLIKELY(_li>=_of->nlinks))_li=_of->nlinks-1;
+  if(!_of->seekable){
+    if(_of->ready_state<OP_STREAMSET&&_of->ready_state!=OP_PARTOPEN){
+      return NULL;
+    }
+    _li=0;
+  }
+  else if(_li<0)_li=_of->ready_state>=OP_STREAMSET?_of->cur_link:0;
+  return &_of->links[_li].tags;
+}
+
+int op_current_link(const OggOpusFile *_of){
+  if(OP_UNLIKELY(_of->ready_state<OP_OPENED))return OP_EINVAL;
+  return _of->cur_link;
+}
+
+/*Compute an average bitrate given a byte and sample count.
+  Return: The bitrate in bits per second.*/
+static opus_int32 op_calc_bitrate(opus_int64 _bytes,ogg_int64_t _samples){
+  /*These rates are absurd, but let's handle them anyway.*/
+  if(OP_UNLIKELY(_bytes>(OP_INT64_MAX-(_samples>>1))/(48000*8))){
+    ogg_int64_t den;
+    if(OP_UNLIKELY(_bytes/(OP_INT32_MAX/(48000*8))>=_samples)){
+      return OP_INT32_MAX;
+    }
+    den=_samples/(48000*8);
+    return (opus_int32)((_bytes+(den>>1))/den);
+  }
+  if(OP_UNLIKELY(_samples<=0))return OP_INT32_MAX;
+  /*This can't actually overflow in normal operation: even with a pre-skip of
+     545 2.5 ms frames with 8 streams running at 1282*8+1 bytes per packet
+     (1275 byte frames + Opus framing overhead + Ogg lacing values), that all
+     produce a single sample of decoded output, we still don't top 45 Mbps.
+    The only way to get bitrates larger than that is with excessive Opus
+     padding, more encoded streams than output channels, or lots and lots of
+     Ogg pages with no packets on them.*/
+  return (opus_int32)OP_MIN((_bytes*48000*8+(_samples>>1))/_samples,
+   OP_INT32_MAX);
+}
+
+opus_int32 op_bitrate(const OggOpusFile *_of,int _li){
+  if(OP_UNLIKELY(_of->ready_state<OP_OPENED)||OP_UNLIKELY(!_of->seekable)
+   ||OP_UNLIKELY(_li>=_of->nlinks)){
+    return OP_EINVAL;
+  }
+  return op_calc_bitrate(op_raw_total(_of,_li),op_pcm_total(_of,_li));
+}
+
+opus_int32 op_bitrate_instant(OggOpusFile *_of){
+  ogg_int64_t samples_tracked;
+  opus_int32  ret;
+  if(OP_UNLIKELY(_of->ready_state<OP_OPENED))return OP_EINVAL;
+  samples_tracked=_of->samples_tracked;
+  if(OP_UNLIKELY(samples_tracked==0))return OP_FALSE;
+  ret=op_calc_bitrate(_of->bytes_tracked,samples_tracked);
+  _of->bytes_tracked=0;
+  _of->samples_tracked=0;
+  return ret;
+}
+
+/*Given a serialno, find a link with a corresponding Opus stream, if it exists.
+  Return: The index of the link to which the page belongs, or a negative number
+           if it was not a desired Opus bitstream section.*/
+static int op_get_link_from_serialno(const OggOpusFile *_of,int _cur_link,
+ opus_int64 _page_offset,ogg_uint32_t _serialno){
+  const OggOpusLink *links;
+  int                nlinks;
+  int                li_lo;
+  int                li_hi;
+  OP_ASSERT(_of->seekable);
+  links=_of->links;
+  nlinks=_of->nlinks;
+  li_lo=0;
+  /*Start off by guessing we're just a multiplexed page in the current link.*/
+  li_hi=_cur_link+1<nlinks&&_page_offset<links[_cur_link+1].offset?
+   _cur_link+1:nlinks;
+  do{
+    if(_page_offset>=links[_cur_link].offset)li_lo=_cur_link;
+    else li_hi=_cur_link;
+    _cur_link=li_lo+(li_hi-li_lo>>1);
+  }
+  while(li_hi-li_lo>1);
+  /*We've identified the link that should contain this page.
+    Make sure it's a page we care about.*/
+  if(links[_cur_link].serialno!=_serialno)return OP_FALSE;
+  return _cur_link;
+}
+
+/*Fetch and process a page.
+  This handles the case where we're at a bitstream boundary and dumps the
+   decoding machine.
+  If the decoding machine is unloaded, it loads it.
+  It also keeps prev_packet_gp up to date (seek and read both use this).
+  Return: <0) Error, OP_HOLE (lost packet), or OP_EOF.
+           0) Got at least one audio data packet.*/
+static int op_fetch_and_process_page(OggOpusFile *_of,
+ ogg_page *_og,opus_int64 _page_offset,int _spanp,int _ignore_holes){
+  OggOpusLink  *links;
+  ogg_uint32_t  cur_serialno;
+  int           seekable;
+  int           cur_link;
+  int           ret;
+  /*We shouldn't get here if we have unprocessed packets.*/
+  OP_ASSERT(_of->ready_state<OP_INITSET||_of->op_pos>=_of->op_count);
+  seekable=_of->seekable;
+  links=_of->links;
+  cur_link=seekable?_of->cur_link:0;
+  cur_serialno=links[cur_link].serialno;
+  /*Handle one page.*/
+  for(;;){
+    ogg_page og;
+    OP_ASSERT(_of->ready_state>=OP_OPENED);
+    /*If we were given a page to use, use it.*/
+    if(_og!=NULL){
+      *&og=*_og;
+      _og=NULL;
+    }
+    /*Keep reading until we get a page with the correct serialno.*/
+    else _page_offset=op_get_next_page(_of,&og,_of->end);
+    /*EOF: Leave uninitialized.*/
+    if(_page_offset<0)return _page_offset<OP_FALSE?(int)_page_offset:OP_EOF;
+    if(OP_LIKELY(_of->ready_state>=OP_STREAMSET)
+     &&cur_serialno!=(ogg_uint32_t)ogg_page_serialno(&og)){
+      /*Two possibilities:
+         1) Another stream is multiplexed into this logical section, or*/
+      if(OP_LIKELY(!ogg_page_bos(&og)))continue;
+      /* 2) Our decoding just traversed a bitstream boundary.*/
+      if(!_spanp)return OP_EOF;
+      if(OP_LIKELY(_of->ready_state>=OP_INITSET))op_decode_clear(_of);
+    }
+    /*Bitrate tracking: add the header's bytes here.
+      The body bytes are counted when we consume the packets.*/
+    else _of->bytes_tracked+=og.header_len;
+    /*Do we need to load a new machine before submitting the page?
+      This is different in the seekable and non-seekable cases.
+      In the seekable case, we already have all the header information loaded
+       and cached.
+      We just initialize the machine with it and continue on our merry way.
+      In the non-seekable (streaming) case, we'll only be at a boundary if we
+       just left the previous logical bitstream, and we're now nominally at the
+       header of the next bitstream.*/
+    if(OP_UNLIKELY(_of->ready_state<OP_STREAMSET)){
+      if(seekable){
+        ogg_uint32_t serialno;
+        serialno=ogg_page_serialno(&og);
+        /*Match the serialno to bitstream section.*/
+        OP_ASSERT(cur_link>=0&&cur_link<_of->nlinks);
+        if(links[cur_link].serialno!=serialno){
+          /*It wasn't a page from the current link.
+            Is it from the next one?*/
+          if(OP_LIKELY(cur_link+1<_of->nlinks&&links[cur_link+1].serialno==
+           serialno)){
+            cur_link++;
+          }
+          else{
+            int new_link;
+            new_link=
+             op_get_link_from_serialno(_of,cur_link,_page_offset,serialno);
+            /*Not a desired Opus bitstream section.
+              Keep trying.*/
+            if(new_link<0)continue;
+            cur_link=new_link;
+          }
+        }
+        cur_serialno=serialno;
+        _of->cur_link=cur_link;
+        ogg_stream_reset_serialno(&_of->os,serialno);
+        _of->ready_state=OP_STREAMSET;
+        /*If we're at the start of this link, initialize the granule position
+           and pre-skip tracking.*/
+        if(_page_offset<=links[cur_link].data_offset){
+          _of->prev_packet_gp=links[cur_link].pcm_start;
+          _of->prev_page_offset=-1;
+          _of->cur_discard_count=links[cur_link].head.pre_skip;
+          /*Ignore a hole at the start of a new link (this is common for
+             streams joined in the middle) or after seeking.*/
+          _ignore_holes=1;
+        }
+      }
+      else{
+        do{
+          /*We're streaming.
+            Fetch the two header packets, build the info struct.*/
+          ret=op_fetch_headers(_of,&links[0].head,&links[0].tags,
+           NULL,NULL,NULL,&og);
+          if(OP_UNLIKELY(ret<0))return ret;
+          /*op_find_initial_pcm_offset() will suppress any initial hole for us,
+             so no need to set _ignore_holes.*/
+          ret=op_find_initial_pcm_offset(_of,links,&og);
+          if(OP_UNLIKELY(ret<0))return ret;
+          _of->links[0].serialno=cur_serialno=_of->os.serialno;
+          _of->cur_link++;
+        }
+        /*If the link was empty, keep going, because we already have the
+           BOS page of the next one in og.*/
+        while(OP_UNLIKELY(ret>0));
+        /*If we didn't get any packets out of op_find_initial_pcm_offset(),
+           keep going (this is possible if end-trimming trimmed them all).*/
+        if(_of->op_count<=0)continue;
+        /*Otherwise, we're done.
+          TODO: This resets bytes_tracked, which misses the header bytes
+           already processed by op_find_initial_pcm_offset().*/
+        ret=op_make_decode_ready(_of);
+        if(OP_UNLIKELY(ret<0))return ret;
+        return 0;
+      }
+    }
+    /*The buffered page is the data we want, and we're ready for it.
+      Add it to the stream state.*/
+    if(OP_UNLIKELY(_of->ready_state==OP_STREAMSET)){
+      ret=op_make_decode_ready(_of);
+      if(OP_UNLIKELY(ret<0))return ret;
+    }
+    /*Extract all the packets from the current page.*/
+    ogg_stream_pagein(&_of->os,&og);
+    if(OP_LIKELY(_of->ready_state>=OP_INITSET)){
+      opus_int32 total_duration;
+      int        durations[255];
+      int        op_count;
+      int        report_hole;
+      report_hole=0;
+      total_duration=op_collect_audio_packets(_of,durations);
+      if(OP_UNLIKELY(total_duration<0)){
+        /*libogg reported a hole (a gap in the page sequence numbers).
+          Drain the packets from the page anyway.
+          If we don't, they'll still be there when we fetch the next page.
+          Then, when we go to pull out packets, we might get more than 255,
+           which would overrun our packet buffer.*/
+        total_duration=op_collect_audio_packets(_of,durations);
+        OP_ASSERT(total_duration>=0);
+        if(!_ignore_holes){
+          /*Report the hole to the caller after we finish timestamping the
+             packets.*/
+          report_hole=1;
+          /*We had lost or damaged pages, so reset our granule position
+             tracking.
+            This makes holes behave the same as a small raw seek.
+            If the next page is the EOS page, we'll discard it (because we
+             can't perform end trimming properly), and we'll always discard at
+             least 80 ms of audio (to allow decoder state to re-converge).
+            We could try to fill in the gap with PLC by looking at timestamps
+             in the non-EOS case, but that's complicated and error prone and we
+             can't rely on the timestamps being valid.*/
+          _of->prev_packet_gp=-1;
+        }
+      }
+      op_count=_of->op_count;
+      /*If we found at least one audio data packet, compute per-packet granule
+         positions for them.*/
+      if(op_count>0){
+        ogg_int64_t diff;
+        ogg_int64_t prev_packet_gp;
+        ogg_int64_t cur_packet_gp;
+        ogg_int64_t cur_page_gp;
+        int         cur_page_eos;
+        int         pi;
+        cur_page_gp=_of->op[op_count-1].granulepos;
+        cur_page_eos=_of->op[op_count-1].e_o_s;
+        prev_packet_gp=_of->prev_packet_gp;
+        if(OP_UNLIKELY(prev_packet_gp==-1)){
+          opus_int32 cur_discard_count;
+          /*This is the first call after a raw seek.
+            Try to reconstruct prev_packet_gp from scratch.*/
+          OP_ASSERT(seekable);
+          if(OP_UNLIKELY(cur_page_eos)){
+            /*If the first page we hit after our seek was the EOS page, and
+               we didn't start from data_offset or before, we don't have
+               enough information to do end-trimming.
+              Proceed to the next link, rather than risk playing back some
+               samples that shouldn't have been played.*/
+            _of->op_count=0;
+            if(report_hole)return OP_HOLE;
+            continue;
+          }
+          /*By default discard 80 ms of data after a seek, unless we seek
+             into the pre-skip region.*/
+          cur_discard_count=80*48;
+          cur_page_gp=_of->op[op_count-1].granulepos;
+          /*Try to initialize prev_packet_gp.
+            If the current page had packets but didn't have a granule
+             position, or the granule position it had was too small (both
+             illegal), just use the starting granule position for the link.*/
+          prev_packet_gp=links[cur_link].pcm_start;
+          if(OP_LIKELY(cur_page_gp!=-1)){
+            op_granpos_add(&prev_packet_gp,cur_page_gp,-total_duration);
+          }
+          if(OP_LIKELY(!op_granpos_diff(&diff,
+           prev_packet_gp,links[cur_link].pcm_start))){
+            opus_int32 pre_skip;
+            /*If we start at the beginning of the pre-skip region, or we're
+               at least 80 ms from the end of the pre-skip region, we discard
+               to the end of the pre-skip region.
+              Otherwise, we still use the 80 ms default, which will discard
+               past the end of the pre-skip region.*/
+            pre_skip=links[cur_link].head.pre_skip;
+            if(diff>=0&&diff<=OP_MAX(0,pre_skip-80*48)){
+              cur_discard_count=pre_skip-(int)diff;
+            }
+          }
+          _of->cur_discard_count=cur_discard_count;
+        }
+        if(OP_UNLIKELY(cur_page_gp==-1)){
+          /*This page had completed packets but didn't have a valid granule
+             position.
+            This is illegal, but we'll try to handle it by continuing to count
+             forwards from the previous page.*/
+          if(op_granpos_add(&cur_page_gp,prev_packet_gp,total_duration)<0){
+            /*The timestamp for this page overflowed.*/
+            cur_page_gp=links[cur_link].pcm_end;
+          }
+        }
+        /*If we hit the last page, handle end-trimming.*/
+        if(OP_UNLIKELY(cur_page_eos)
+         &&OP_LIKELY(!op_granpos_diff(&diff,cur_page_gp,prev_packet_gp))
+         &&OP_LIKELY(diff<total_duration)){
+          cur_packet_gp=prev_packet_gp;
+          for(pi=0;pi<op_count;pi++){
+            /*Check for overflow.*/
+            if(diff<0&&OP_UNLIKELY(OP_INT64_MAX+diff<durations[pi])){
+              diff=durations[pi]+1;
+            }
+            else diff=durations[pi]-diff;
+            /*If we have samples to trim...*/
+            if(diff>0){
+              /*If we trimmed the entire packet, stop (the spec says encoders
+                 shouldn't do this, but we support it anyway).*/
+              if(OP_UNLIKELY(diff>durations[pi]))break;
+              cur_packet_gp=cur_page_gp;
+              /*Move the EOS flag to this packet, if necessary, so we'll trim
+                 the samples during decode.*/
+              _of->op[pi].e_o_s=1;
+            }
+            else{
+              /*Update the granule position as normal.*/
+              OP_ALWAYS_TRUE(!op_granpos_add(&cur_packet_gp,
+               cur_packet_gp,durations[pi]));
+            }
+            _of->op[pi].granulepos=cur_packet_gp;
+            OP_ALWAYS_TRUE(!op_granpos_diff(&diff,cur_page_gp,cur_packet_gp));
+          }
+        }
+        else{
+          /*Propagate timestamps to earlier packets.
+            op_granpos_add(&prev_packet_gp,prev_packet_gp,total_duration)
+             should succeed and give prev_packet_gp==cur_page_gp.
+            But we don't bother to check that, as there isn't much we can do
+             if it's not true, and it actually will not be true on the first
+             page after a seek, if there was a continued packet.
+            The only thing we guarantee is that the start and end granule
+             positions of the packets are valid, and that they are monotonic
+             within a page.
+            They might be completely out of range for this link (we'll check
+             that elsewhere), or non-monotonic between pages.*/
+          if(OP_UNLIKELY(op_granpos_add(&prev_packet_gp,
+           cur_page_gp,-total_duration)<0)){
+            /*The starting timestamp for the first packet on this page
+               underflowed.
+              This is illegal, but we ignore it.*/
+            prev_packet_gp=0;
+          }
+          for(pi=0;pi<op_count;pi++){
+            if(OP_UNLIKELY(op_granpos_add(&cur_packet_gp,
+             cur_page_gp,-total_duration)<0)){
+              /*The start timestamp for this packet underflowed.
+                This is illegal, but we ignore it.*/
+              cur_packet_gp=0;
+            }
+            total_duration-=durations[pi];
+            OP_ASSERT(total_duration>=0);
+            OP_ALWAYS_TRUE(!op_granpos_add(&cur_packet_gp,
+             cur_packet_gp,durations[pi]));
+            _of->op[pi].granulepos=cur_packet_gp;
+          }
+          OP_ASSERT(total_duration==0);
+        }
+        _of->prev_packet_gp=prev_packet_gp;
+        _of->prev_page_offset=_page_offset;
+        _of->op_count=op_count=pi;
+      }
+      if(report_hole)return OP_HOLE;
+      /*If end-trimming didn't trim all the packets, we're done.*/
+      if(op_count>0)return 0;
+    }
+  }
+}
+
+int op_raw_seek(OggOpusFile *_of,opus_int64 _pos){
+  int ret;
+  if(OP_UNLIKELY(_of->ready_state<OP_OPENED))return OP_EINVAL;
+  /*Don't dump the decoder state if we can't seek.*/
+  if(OP_UNLIKELY(!_of->seekable))return OP_ENOSEEK;
+  if(OP_UNLIKELY(_pos<0)||OP_UNLIKELY(_pos>_of->end))return OP_EINVAL;
+  /*Clear out any buffered, decoded data.*/
+  op_decode_clear(_of);
+  _of->bytes_tracked=0;
+  _of->samples_tracked=0;
+  ret=op_seek_helper(_of,_pos);
+  if(OP_UNLIKELY(ret<0))return OP_EREAD;
+  ret=op_fetch_and_process_page(_of,NULL,-1,1,1);
+  /*If we hit EOF, op_fetch_and_process_page() leaves us uninitialized.
+    Instead, jump to the end.*/
+  if(ret==OP_EOF){
+    int cur_link;
+    op_decode_clear(_of);
+    cur_link=_of->nlinks-1;
+    _of->cur_link=cur_link;
+    _of->prev_packet_gp=_of->links[cur_link].pcm_end;
+    _of->cur_discard_count=0;
+    ret=0;
+  }
+  return ret;
+}
+
+/*Convert a PCM offset relative to the start of the whole stream to a granule
+   position in an individual link.*/
+static ogg_int64_t op_get_granulepos(const OggOpusFile *_of,
+ ogg_int64_t _pcm_offset,int *_li){
+  const OggOpusLink *links;
+  ogg_int64_t        duration;
+  ogg_int64_t        pcm_start;
+  opus_int32         pre_skip;
+  int                nlinks;
+  int                li_lo;
+  int                li_hi;
+  OP_ASSERT(_pcm_offset>=0);
+  nlinks=_of->nlinks;
+  links=_of->links;
+  li_lo=0;
+  li_hi=nlinks;
+  do{
+    int li;
+    li=li_lo+(li_hi-li_lo>>1);
+    if(links[li].pcm_file_offset<=_pcm_offset)li_lo=li;
+    else li_hi=li;
+  }
+  while(li_hi-li_lo>1);
+  _pcm_offset-=links[li_lo].pcm_file_offset;
+  pcm_start=links[li_lo].pcm_start;
+  pre_skip=links[li_lo].head.pre_skip;
+  OP_ALWAYS_TRUE(!op_granpos_diff(&duration,links[li_lo].pcm_end,pcm_start));
+  duration-=pre_skip;
+  if(_pcm_offset>=duration)return -1;
+  _pcm_offset+=pre_skip;
+  if(OP_UNLIKELY(pcm_start>OP_INT64_MAX-_pcm_offset)){
+    /*Adding this amount to the granule position would overflow the positive
+       half of its 64-bit range.
+      Since signed overflow is undefined in C, do it in a way the compiler
+       isn't allowed to screw up.*/
+    _pcm_offset-=OP_INT64_MAX-pcm_start+1;
+    pcm_start=OP_INT64_MIN;
+  }
+  pcm_start+=_pcm_offset;
+  *_li=li_lo;
+  return pcm_start;
+}
+
+/*A small helper to determine if an Ogg page contains data that continues onto
+   a subsequent page.*/
+static int op_page_continues(const ogg_page *_og){
+  int nlacing;
+  OP_ASSERT(_og->header_len>=27);
+  nlacing=_og->header[26];
+  OP_ASSERT(_og->header_len>=27+nlacing);
+  /*This also correctly handles the (unlikely) case of nlacing==0, because
+     0!=255.*/
+  return _og->header[27+nlacing-1]==255;
+}
+
+/*A small helper to buffer the continued packet data from a page.*/
+static void op_buffer_continued_data(OggOpusFile *_of,ogg_page *_og){
+  ogg_packet op;
+  ogg_stream_pagein(&_of->os,_og);
+  /*Drain any packets that did end on this page (and ignore holes).
+    We only care about the continued packet data.*/
+  while(ogg_stream_packetout(&_of->os,&op));
+}
+
+/*This controls how close the target has to be to use the current stream
+   position to subdivide the initial range.
+  Two minutes seems to be a good default.*/
+#define OP_CUR_TIME_THRESH (120*48*(opus_int32)1000)
+
+/*Note: The OP_SMALL_FOOTPRINT #define doesn't (currently) save much code size,
+   but it's meant to serve as documentation for portions of the seeking
+   algorithm that are purely optional, to aid others learning from/porting this
+   code to other contexts.*/
+/*#define OP_SMALL_FOOTPRINT (1)*/
+
+/*Search within link _li for the page with the highest granule position
+   preceding (or equal to) _target_gp.
+  There is a danger here: missing pages or incorrect frame number information
+   in the bitstream could make our task impossible.
+  Account for that (and report it as an error condition).*/
+static int op_pcm_seek_page(OggOpusFile *_of,
+ ogg_int64_t _target_gp,int _li){
+  const OggOpusLink *link;
+  ogg_page           og;
+  ogg_int64_t        pcm_pre_skip;
+  ogg_int64_t        pcm_start;
+  ogg_int64_t        pcm_end;
+  ogg_int64_t        best_gp;
+  ogg_int64_t        diff;
+  ogg_uint32_t       serialno;
+  opus_int32         pre_skip;
+  opus_int64         begin;
+  opus_int64         end;
+  opus_int64         boundary;
+  opus_int64         best;
+  opus_int64         best_start;
+  opus_int64         page_offset;
+  opus_int64         d0;
+  opus_int64         d1;
+  opus_int64         d2;
+  int                force_bisect;
+  int                buffering;
+  int                ret;
+  _of->bytes_tracked=0;
+  _of->samples_tracked=0;
+  link=_of->links+_li;
+  best_gp=pcm_start=link->pcm_start;
+  pcm_end=link->pcm_end;
+  serialno=link->serialno;
+  best=best_start=begin=link->data_offset;
+  page_offset=-1;
+  buffering=0;
+  /*We discard the first 80 ms of data after a seek, so seek back that much
+     farther.
+    If we can't, simply seek to the beginning of the link.*/
+  if(OP_UNLIKELY(op_granpos_add(&_target_gp,_target_gp,-80*48)<0)
+   ||OP_UNLIKELY(op_granpos_cmp(_target_gp,pcm_start)<0)){
+    _target_gp=pcm_start;
+  }
+  /*Special case seeking to the start of the link.*/
+  pre_skip=link->head.pre_skip;
+  OP_ALWAYS_TRUE(!op_granpos_add(&pcm_pre_skip,pcm_start,pre_skip));
+  if(op_granpos_cmp(_target_gp,pcm_pre_skip)<0)end=boundary=begin;
+  else{
+    end=boundary=link->end_offset;
+#if !defined(OP_SMALL_FOOTPRINT)
+    /*If we were decoding from this link, we can narrow the range a bit.*/
+    if(_li==_of->cur_link&&_of->ready_state>=OP_INITSET){
+      opus_int64 offset;
+      int        op_count;
+      op_count=_of->op_count;
+      /*The only way the offset can be invalid _and_ we can fail the granule
+         position checks below is if someone changed the contents of the last
+         page since we read it.
+        We'd be within our rights to just return OP_EBADLINK in that case, but
+         we'll simply ignore the current position instead.*/
+      offset=_of->offset;
+      if(op_count>0&&OP_LIKELY(offset<=end)){
+        ogg_int64_t gp;
+        /*Make sure the timestamp is valid.
+          The granule position might be -1 if we collected the packets from a
+           page without a granule position after reporting a hole.*/
+        gp=_of->op[op_count-1].granulepos;
+        if(OP_LIKELY(gp!=-1)&&OP_LIKELY(op_granpos_cmp(pcm_start,gp)<0)
+         &&OP_LIKELY(op_granpos_cmp(pcm_end,gp)>0)){
+          OP_ALWAYS_TRUE(!op_granpos_diff(&diff,gp,_target_gp));
+          /*We only actually use the current time if either
+            a) We can cut off at least half the range, or
+            b) We're seeking sufficiently close to the current position that
+                it's likely to be informative.
+            Otherwise it appears using the whole link range to estimate the
+             first seek location gives better results, on average.*/
+          if(diff<0){
+            OP_ASSERT(offset>=begin);
+            if(offset-begin>=end-begin>>1||diff>-OP_CUR_TIME_THRESH){
+              best=begin=offset;
+              best_gp=pcm_start=gp;
+              /*If we have buffered data from a continued packet, remember the
+                 offset of the previous page's start, so that if we do wind up
+                 having to seek back here later, we can prime the stream with
+                 the continued packet data.
+                With no continued packet, we remember the end of the page.*/
+              best_start=_of->os.body_returned<_of->os.body_fill?
+               _of->prev_page_offset:best;
+              /*If there's completed packets and data in the stream state,
+                 prev_page_offset should always be set.*/
+              OP_ASSERT(best_start>=0);
+              /*Buffer any continued packet data starting from here.*/
+              buffering=1;
+            }
+          }
+          else{
+            ogg_int64_t prev_page_gp;
+            /*We might get lucky and already have the packet with the target
+               buffered.
+              Worth checking.
+              For very small files (with all of the data in a single page,
+               generally 1 second or less), we can loop them continuously
+               without seeking at all.*/
+            OP_ALWAYS_TRUE(!op_granpos_add(&prev_page_gp,_of->op[0].granulepos,
+             -op_get_packet_duration(_of->op[0].packet,_of->op[0].bytes)));
+            if(op_granpos_cmp(prev_page_gp,_target_gp)<=0){
+              /*Don't call op_decode_clear(), because it will dump our
+                 packets.*/
+              _of->op_pos=0;
+              _of->od_buffer_size=0;
+              _of->prev_packet_gp=prev_page_gp;
+              /*_of->prev_page_offset already points to the right place.*/
+              _of->ready_state=OP_STREAMSET;
+              return op_make_decode_ready(_of);
+            }
+            /*No such luck.
+              Check if we can cut off at least half the range, though.*/
+            if(offset-begin<=end-begin>>1||diff<OP_CUR_TIME_THRESH){
+              /*We really want the page start here, but this will do.*/
+              end=boundary=offset;
+              pcm_end=gp;
+            }
+          }
+        }
+      }
+    }
+#endif
+  }
+  /*This code was originally based on the "new search algorithm by HB (Nicholas
+     Vinen)" from libvorbisfile.
+    It has been modified substantially since.*/
+  op_decode_clear(_of);
+  if(!buffering)ogg_stream_reset_serialno(&_of->os,serialno);
+  _of->cur_link=_li;
+  _of->ready_state=OP_STREAMSET;
+  /*Initialize the interval size history.*/
+  d2=d1=d0=end-begin;
+  force_bisect=0;
+  while(begin<end){
+    opus_int64 bisect;
+    opus_int64 next_boundary;
+    opus_int32 chunk_size;
+    if(end-begin<OP_CHUNK_SIZE)bisect=begin;
+    else{
+      /*Update the interval size history.*/
+      d0=d1>>1;
+      d1=d2>>1;
+      d2=end-begin>>1;
+      if(force_bisect)bisect=begin+(end-begin>>1);
+      else{
+        ogg_int64_t diff2;
+        OP_ALWAYS_TRUE(!op_granpos_diff(&diff,_target_gp,pcm_start));
+        OP_ALWAYS_TRUE(!op_granpos_diff(&diff2,pcm_end,pcm_start));
+        /*Take a (pretty decent) guess.*/
+        bisect=begin+op_rescale64(diff,diff2,end-begin)-OP_CHUNK_SIZE;
+      }
+      if(bisect-OP_CHUNK_SIZE<begin)bisect=begin;
+      force_bisect=0;
+    }
+    if(bisect!=_of->offset){
+      /*Discard any buffered continued packet data.*/
+      if(buffering)ogg_stream_reset(&_of->os);
+      buffering=0;
+      page_offset=-1;
+      ret=op_seek_helper(_of,bisect);
+      if(OP_UNLIKELY(ret<0))return ret;
+    }
+    chunk_size=OP_CHUNK_SIZE;
+    next_boundary=boundary;
+    /*Now scan forward and figure out where we landed.
+      In the ideal case, we will see a page with a granule position at or
+       before our target, followed by a page with a granule position after our
+       target (or the end of the search interval).
+      Then we can just drop out and will have all of the data we need with no
+       additional seeking.
+      If we landed too far before, or after, we'll break out and do another
+       bisection.*/
+    while(begin<end){
+      page_offset=op_get_next_page(_of,&og,boundary);
+      if(page_offset<0){
+        if(page_offset<OP_FALSE)return (int)page_offset;
+        /*There are no more pages in our interval from our stream with a valid
+           timestamp that start at position bisect or later.*/
+        /*If we scanned the whole interval, we're done.*/
+        if(bisect<=begin+1)end=begin;
+        else{
+          /*Otherwise, back up one chunk.
+            First, discard any data from a continued packet.*/
+          if(buffering)ogg_stream_reset(&_of->os);
+          buffering=0;
+          bisect=OP_MAX(bisect-chunk_size,begin);
+          ret=op_seek_helper(_of,bisect);
+          if(OP_UNLIKELY(ret<0))return ret;
+          /*Bump up the chunk size.*/
+          chunk_size=OP_MIN(2*chunk_size,OP_CHUNK_SIZE_MAX);
+          /*If we did find a page from another stream or without a timestamp,
+             don't read past it.*/
+          boundary=next_boundary;
+        }
+      }
+      else{
+        ogg_int64_t gp;
+        int         has_packets;
+        /*Save the offset of the first page we found after the seek, regardless
+           of the stream it came from or whether or not it has a timestamp.*/
+        next_boundary=OP_MIN(page_offset,next_boundary);
+        if(serialno!=(ogg_uint32_t)ogg_page_serialno(&og))continue;
+        has_packets=ogg_page_packets(&og)>0;
+        /*Force the gp to -1 (as it should be per spec) if no packets end on
+           this page.
+          Otherwise we might get confused when we try to pull out a packet
+           with that timestamp and can't find it.*/
+        gp=has_packets?ogg_page_granulepos(&og):-1;
+        if(gp==-1){
+          if(buffering){
+            if(OP_LIKELY(!has_packets))ogg_stream_pagein(&_of->os,&og);
+            else{
+              /*If packets did end on this page, but we still didn't have a
+                 valid granule position (in violation of the spec!), stop
+                 buffering continued packet data.
+                Otherwise we might continue past the packet we actually
+                 wanted.*/
+              ogg_stream_reset(&_of->os);
+              buffering=0;
+            }
+          }
+          continue;
+        }
+        if(op_granpos_cmp(gp,_target_gp)<0){
+          /*We found a page that ends before our target.
+            Advance to the raw offset of the next page.*/
+          begin=_of->offset;
+          if(OP_UNLIKELY(op_granpos_cmp(pcm_start,gp)>0)
+           ||OP_UNLIKELY(op_granpos_cmp(pcm_end,gp)<0)){
+            /*Don't let pcm_start get out of range!
+              That could happen with an invalid timestamp.*/
+            break;
+          }
+          /*Save the byte offset of the end of the page with this granule
+             position.*/
+          best=best_start=begin;
+          /*Buffer any data from a continued packet, if necessary.
+            This avoids the need to seek back here if the next timestamp we
+             encounter while scanning forward lies after our target.*/
+          if(buffering)ogg_stream_reset(&_of->os);
+          if(op_page_continues(&og)){
+            op_buffer_continued_data(_of,&og);
+            /*If we have a continued packet, remember the offset of this
+               page's start, so that if we do wind up having to seek back here
+               later, we can prime the stream with the continued packet data.
+              With no continued packet, we remember the end of the page.*/
+            best_start=page_offset;
+          }
+          /*Then force buffering on, so that if a packet starts (but does not
+             end) on the next page, we still avoid the extra seek back.*/
+          buffering=1;
+          best_gp=pcm_start=gp;
+          OP_ALWAYS_TRUE(!op_granpos_diff(&diff,_target_gp,pcm_start));
+          /*If we're more than a second away from our target, break out and
+             do another bisection.*/
+          if(diff>48000)break;
+          /*Otherwise, keep scanning forward (do NOT use begin+1).*/
+          bisect=begin;
+        }
+        else{
+          /*We found a page that ends after our target.*/
+          /*If we scanned the whole interval before we found it, we're done.*/
+          if(bisect<=begin+1)end=begin;
+          else{
+            end=bisect;
+            /*In later iterations, don't read past the first page we found.*/
+            boundary=next_boundary;
+            /*If we're not making much progress shrinking the interval size,
+               start forcing straight bisection to limit the worst case.*/
+            force_bisect=end-begin>d0*2;
+            /*Don't let pcm_end get out of range!
+              That could happen with an invalid timestamp.*/
+            if(OP_LIKELY(op_granpos_cmp(pcm_end,gp)>0)
+             &&OP_LIKELY(op_granpos_cmp(pcm_start,gp)<=0)){
+              pcm_end=gp;
+            }
+            break;
+          }
+        }
+      }
+    }
+  }
+  /*Found our page.*/
+  OP_ASSERT(op_granpos_cmp(best_gp,pcm_start)>=0);
+  /*Seek, if necessary.
+    If we were buffering data from a continued packet, we should be able to
+     continue to scan forward to get the rest of the data (even if
+     page_offset==-1).
+    Otherwise, we need to seek back to best_start.*/
+  if(!buffering){
+    if(best_start!=page_offset){
+      page_offset=-1;
+      ret=op_seek_helper(_of,best_start);
+      if(OP_UNLIKELY(ret<0))return ret;
+    }
+    if(best_start<best){
+      /*Retrieve the page at best_start, if we do not already have it.*/
+      if(page_offset<0){
+        page_offset=op_get_next_page(_of,&og,link->end_offset);
+        if(OP_UNLIKELY(page_offset<OP_FALSE))return (int)page_offset;
+        if(OP_UNLIKELY(page_offset!=best_start))return OP_EBADLINK;
+      }
+      op_buffer_continued_data(_of,&og);
+      page_offset=-1;
+    }
+  }
+  /*Update prev_packet_gp to allow per-packet granule position assignment.*/
+  _of->prev_packet_gp=best_gp;
+  _of->prev_page_offset=best_start;
+  ret=op_fetch_and_process_page(_of,page_offset<0?NULL:&og,page_offset,0,1);
+  if(OP_UNLIKELY(ret<0))return OP_EBADLINK;
+  /*Verify result.*/
+  if(OP_UNLIKELY(op_granpos_cmp(_of->prev_packet_gp,_target_gp)>0)){
+    return OP_EBADLINK;
+  }
+  /*Our caller will set cur_discard_count to handle pre-roll.*/
+  return 0;
+}
+
+int op_pcm_seek(OggOpusFile *_of,ogg_int64_t _pcm_offset){
+  const OggOpusLink *link;
+  ogg_int64_t        pcm_start;
+  ogg_int64_t        target_gp;
+  ogg_int64_t        prev_packet_gp;
+  ogg_int64_t        skip;
+  ogg_int64_t        diff;
+  int                op_count;
+  int                op_pos;
+  int                ret;
+  int                li;
+  if(OP_UNLIKELY(_of->ready_state<OP_OPENED))return OP_EINVAL;
+  if(OP_UNLIKELY(!_of->seekable))return OP_ENOSEEK;
+  if(OP_UNLIKELY(_pcm_offset<0))return OP_EINVAL;
+  target_gp=op_get_granulepos(_of,_pcm_offset,&li);
+  if(OP_UNLIKELY(target_gp==-1))return OP_EINVAL;
+  link=_of->links+li;
+  pcm_start=link->pcm_start;
+  OP_ALWAYS_TRUE(!op_granpos_diff(&_pcm_offset,target_gp,pcm_start));
+#if !defined(OP_SMALL_FOOTPRINT)
+  /*For small (90 ms or less) forward seeks within the same link, just decode
+     forward.
+    This also optimizes the case of seeking to the current position.*/
+  if(li==_of->cur_link&&_of->ready_state>=OP_INITSET){
+    ogg_int64_t gp;
+    gp=_of->prev_packet_gp;
+    if(OP_LIKELY(gp!=-1)){
+      ogg_int64_t discard_count;
+      int         nbuffered;
+      nbuffered=OP_MAX(_of->od_buffer_size-_of->od_buffer_pos,0);
+      OP_ALWAYS_TRUE(!op_granpos_add(&gp,gp,-nbuffered));
+      /*We do _not_ add cur_discard_count to gp.
+        Otherwise the total amount to discard could grow without bound, and it
+         would be better just to do a full seek.*/
+      if(OP_LIKELY(!op_granpos_diff(&discard_count,target_gp,gp))){
+        /*We use a threshold of 90 ms instead of 80, since 80 ms is the
+           _minimum_ we would have discarded after a full seek.
+          Assuming 20 ms frames (the default), we'd discard 90 ms on average.*/
+        if(discard_count>=0&&OP_UNLIKELY(discard_count<90*48)){
+          _of->cur_discard_count=(opus_int32)discard_count;
+          return 0;
+        }
+      }
+    }
+  }
+#endif
+  ret=op_pcm_seek_page(_of,target_gp,li);
+  if(OP_UNLIKELY(ret<0))return ret;
+  /*Now skip samples until we actually get to our target.*/
+  /*Figure out where we should skip to.*/
+  if(_pcm_offset<=link->head.pre_skip)skip=0;
+  else skip=OP_MAX(_pcm_offset-80*48,0);
+  OP_ASSERT(_pcm_offset-skip>=0);
+  OP_ASSERT(_pcm_offset-skip<OP_INT32_MAX-120*48);
+  /*Skip packets until we find one with samples past our skip target.*/
+  for(;;){
+    op_count=_of->op_count;
+    prev_packet_gp=_of->prev_packet_gp;
+    for(op_pos=_of->op_pos;op_pos<op_count;op_pos++){
+      ogg_int64_t cur_packet_gp;
+      cur_packet_gp=_of->op[op_pos].granulepos;
+      if(OP_LIKELY(!op_granpos_diff(&diff,cur_packet_gp,pcm_start))
+       &&diff>skip){
+        break;
+      }
+      prev_packet_gp=cur_packet_gp;
+    }
+    _of->prev_packet_gp=prev_packet_gp;
+    _of->op_pos=op_pos;
+    if(op_pos<op_count)break;
+    /*We skipped all the packets on this page.
+      Fetch another.*/
+    ret=op_fetch_and_process_page(_of,NULL,-1,0,1);
+    if(OP_UNLIKELY(ret<0))return OP_EBADLINK;
+  }
+  OP_ALWAYS_TRUE(!op_granpos_diff(&diff,prev_packet_gp,pcm_start));
+  /*We skipped too far.
+    Either the timestamps were illegal or there was a hole in the data.*/
+  if(diff>skip)return OP_EBADLINK;
+  OP_ASSERT(_pcm_offset-diff<OP_INT32_MAX);
+  /*TODO: If there are further holes/illegal timestamps, we still won't decode
+     to the correct sample.
+    However, at least op_pcm_tell() will report the correct value immediately
+     after returning.*/
+  _of->cur_discard_count=(opus_int32)(_pcm_offset-diff);
+  return 0;
+}
+
+opus_int64 op_raw_tell(const OggOpusFile *_of){
+  if(OP_UNLIKELY(_of->ready_state<OP_OPENED))return OP_EINVAL;
+  return _of->offset;
+}
+
+/*Convert a granule position from a given link to a PCM offset relative to the
+   start of the whole stream.
+  For unseekable sources, this gets reset to 0 at the beginning of each link.*/
+static ogg_int64_t op_get_pcm_offset(const OggOpusFile *_of,
+ ogg_int64_t _gp,int _li){
+  const OggOpusLink *links;
+  ogg_int64_t        pcm_offset;
+  links=_of->links;
+  OP_ASSERT(_li>=0&&_li<_of->nlinks);
+  pcm_offset=links[_li].pcm_file_offset;
+  if(_of->seekable&&OP_UNLIKELY(op_granpos_cmp(_gp,links[_li].pcm_end)>0)){
+    _gp=links[_li].pcm_end;
+  }
+  if(OP_LIKELY(op_granpos_cmp(_gp,links[_li].pcm_start)>0)){
+    ogg_int64_t delta;
+    if(OP_UNLIKELY(op_granpos_diff(&delta,_gp,links[_li].pcm_start)<0)){
+      /*This means an unseekable stream claimed to have a page from more than
+         2 billion days after we joined.*/
+      OP_ASSERT(!_of->seekable);
+      return OP_INT64_MAX;
+    }
+    if(delta<links[_li].head.pre_skip)delta=0;
+    else delta-=links[_li].head.pre_skip;
+    /*In the seekable case, _gp was limited by pcm_end.
+      In the unseekable case, pcm_offset should be 0.*/
+    OP_ASSERT(pcm_offset<=OP_INT64_MAX-delta);
+    pcm_offset+=delta;
+  }
+  return pcm_offset;
+}
+
+ogg_int64_t op_pcm_tell(const OggOpusFile *_of){
+  ogg_int64_t gp;
+  int         nbuffered;
+  int         li;
+  if(OP_UNLIKELY(_of->ready_state<OP_OPENED))return OP_EINVAL;
+  gp=_of->prev_packet_gp;
+  if(gp==-1)return 0;
+  nbuffered=OP_MAX(_of->od_buffer_size-_of->od_buffer_pos,0);
+  OP_ALWAYS_TRUE(!op_granpos_add(&gp,gp,-nbuffered));
+  li=_of->seekable?_of->cur_link:0;
+  if(op_granpos_add(&gp,gp,_of->cur_discard_count)<0){
+    gp=_of->links[li].pcm_end;
+  }
+  return op_get_pcm_offset(_of,gp,li);
+}
+
+void op_set_decode_callback(OggOpusFile *_of,
+ op_decode_cb_func _decode_cb,void *_ctx){
+  _of->decode_cb=_decode_cb;
+  _of->decode_cb_ctx=_ctx;
+}
+
+int op_set_gain_offset(OggOpusFile *_of,
+ int _gain_type,opus_int32 _gain_offset_q8){
+  if(_gain_type!=OP_HEADER_GAIN&&_gain_type!=OP_ALBUM_GAIN
+   &&_gain_type!=OP_TRACK_GAIN&&_gain_type!=OP_ABSOLUTE_GAIN){
+    return OP_EINVAL;
+  }
+  _of->gain_type=_gain_type;
+  /*The sum of header gain and track gain lies in the range [-65536,65534].
+    These bounds allow the offset to set the final value to anywhere in the
+     range [-32768,32767], which is what we'll clamp it to before applying.*/
+  _of->gain_offset_q8=OP_CLAMP(-98302,_gain_offset_q8,98303);
+  op_update_gain(_of);
+  return 0;
+}
+
+void op_set_dither_enabled(OggOpusFile *_of,int _enabled){
+#if !defined(OP_FIXED_POINT)
+  _of->dither_disabled=!_enabled;
+  if(!_enabled)_of->dither_mute=65;
+#endif
+}
+
+/*Allocate the decoder scratch buffer.
+  This is done lazily, since if the user provides large enough buffers, we'll
+   never need it.*/
+static int op_init_buffer(OggOpusFile *_of){
+  int nchannels_max;
+  if(_of->seekable){
+    const OggOpusLink *links;
+    int                nlinks;
+    int                li;
+    links=_of->links;
+    nlinks=_of->nlinks;
+    nchannels_max=1;
+    for(li=0;li<nlinks;li++){
+      nchannels_max=OP_MAX(nchannels_max,links[li].head.channel_count);
+    }
+  }
+  else nchannels_max=OP_NCHANNELS_MAX;
+  _of->od_buffer=(op_sample *)_ogg_malloc(
+   sizeof(*_of->od_buffer)*nchannels_max*120*48);
+  if(_of->od_buffer==NULL)return OP_EFAULT;
+  return 0;
+}
+
+/*Decode a single packet into the target buffer.*/
+static int op_decode(OggOpusFile *_of,op_sample *_pcm,
+ const ogg_packet *_op,int _nsamples,int _nchannels){
+  int ret;
+  /*First we try using the application-provided decode callback.*/
+  if(_of->decode_cb!=NULL){
+#if defined(OP_FIXED_POINT)
+    ret=(*_of->decode_cb)(_of->decode_cb_ctx,_of->od,_pcm,_op,
+     _nsamples,_nchannels,OP_DEC_FORMAT_SHORT,_of->cur_link);
+#else
+    ret=(*_of->decode_cb)(_of->decode_cb_ctx,_of->od,_pcm,_op,
+     _nsamples,_nchannels,OP_DEC_FORMAT_FLOAT,_of->cur_link);
+#endif
+  }
+  else ret=OP_DEC_USE_DEFAULT;
+  /*If the application didn't want to handle decoding, do it ourselves.*/
+  if(ret==OP_DEC_USE_DEFAULT){
+#if defined(OP_FIXED_POINT)
+    ret=opus_multistream_decode(_of->od,
+     _op->packet,_op->bytes,_pcm,_nsamples,0);
+#else
+    ret=opus_multistream_decode_float(_of->od,
+     _op->packet,_op->bytes,_pcm,_nsamples,0);
+#endif
+    OP_ASSERT(ret<0||ret==_nsamples);
+  }
+  /*If the application returned a positive value other than 0 or
+     OP_DEC_USE_DEFAULT, fail.*/
+  else if(OP_UNLIKELY(ret>0))return OP_EBADPACKET;
+  if(OP_UNLIKELY(ret<0))return OP_EBADPACKET;
+  return ret;
+}
+
+/*Read more samples from the stream, using the same API as op_read() or
+   op_read_float().*/
+static int op_read_native(OggOpusFile *_of,
+ op_sample *_pcm,int _buf_size,int *_li){
+  if(OP_UNLIKELY(_of->ready_state<OP_OPENED))return OP_EINVAL;
+  for(;;){
+    int ret;
+    if(OP_LIKELY(_of->ready_state>=OP_INITSET)){
+      int nchannels;
+      int od_buffer_pos;
+      int nsamples;
+      int op_pos;
+      nchannels=_of->links[_of->seekable?_of->cur_link:0].head.channel_count;
+      od_buffer_pos=_of->od_buffer_pos;
+      nsamples=_of->od_buffer_size-od_buffer_pos;
+      /*If we have buffered samples, return them.*/
+      if(nsamples>0){
+        if(nsamples*nchannels>_buf_size)nsamples=_buf_size/nchannels;
+        memcpy(_pcm,_of->od_buffer+nchannels*od_buffer_pos,
+         sizeof(*_pcm)*nchannels*nsamples);
+        od_buffer_pos+=nsamples;
+        _of->od_buffer_pos=od_buffer_pos;
+        if(_li!=NULL)*_li=_of->cur_link;
+        return nsamples;
+      }
+      /*If we have buffered packets, decode one.*/
+      op_pos=_of->op_pos;
+      if(OP_LIKELY(op_pos<_of->op_count)){
+        const ogg_packet *pop;
+        ogg_int64_t       diff;
+        opus_int32        cur_discard_count;
+        int               duration;
+        int               trimmed_duration;
+        pop=_of->op+op_pos++;
+        _of->op_pos=op_pos;
+        cur_discard_count=_of->cur_discard_count;
+        duration=op_get_packet_duration(pop->packet,pop->bytes);
+        /*We don't buffer packets with an invalid TOC sequence.*/
+        OP_ASSERT(duration>0);
+        trimmed_duration=duration;
+        /*Perform end-trimming.*/
+        if(OP_UNLIKELY(pop->e_o_s)){
+          if(OP_UNLIKELY(op_granpos_cmp(pop->granulepos,
+           _of->prev_packet_gp)<=0)){
+            trimmed_duration=0;
+          }
+          else if(OP_LIKELY(!op_granpos_diff(&diff,
+           pop->granulepos,_of->prev_packet_gp))){
+            trimmed_duration=(int)OP_MIN(diff,trimmed_duration);
+          }
+        }
+        _of->prev_packet_gp=pop->granulepos;
+        if(OP_UNLIKELY(duration*nchannels>_buf_size)){
+          op_sample *buf;
+          /*If the user's buffer is too small, decode into a scratch buffer.*/
+          buf=_of->od_buffer;
+          if(OP_UNLIKELY(buf==NULL)){
+            ret=op_init_buffer(_of);
+            if(OP_UNLIKELY(ret<0))return ret;
+            buf=_of->od_buffer;
+          }
+          ret=op_decode(_of,buf,pop,duration,nchannels);
+          if(OP_UNLIKELY(ret<0))return ret;
+          /*Perform pre-skip/pre-roll.*/
+          od_buffer_pos=(int)OP_MIN(trimmed_duration,cur_discard_count);
+          cur_discard_count-=od_buffer_pos;
+          _of->cur_discard_count=cur_discard_count;
+          _of->od_buffer_pos=od_buffer_pos;
+          _of->od_buffer_size=trimmed_duration;
+          /*Update bitrate tracking based on the actual samples we used from
+             what was decoded.*/
+          _of->bytes_tracked+=pop->bytes;
+          _of->samples_tracked+=trimmed_duration-od_buffer_pos;
+        }
+        else{
+          /*Otherwise decode directly into the user's buffer.*/
+          ret=op_decode(_of,_pcm,pop,duration,nchannels);
+          if(OP_UNLIKELY(ret<0))return ret;
+          if(OP_LIKELY(trimmed_duration>0)){
+            /*Perform pre-skip/pre-roll.*/
+            od_buffer_pos=(int)OP_MIN(trimmed_duration,cur_discard_count);
+            cur_discard_count-=od_buffer_pos;
+            _of->cur_discard_count=cur_discard_count;
+            trimmed_duration-=od_buffer_pos;
+            if(OP_LIKELY(trimmed_duration>0)
+             &&OP_UNLIKELY(od_buffer_pos>0)){
+              memmove(_pcm,_pcm+od_buffer_pos*nchannels,
+               sizeof(*_pcm)*trimmed_duration*nchannels);
+            }
+            /*Update bitrate tracking based on the actual samples we used from
+               what was decoded.*/
+            _of->bytes_tracked+=pop->bytes;
+            _of->samples_tracked+=trimmed_duration;
+            if(OP_LIKELY(trimmed_duration>0)){
+              if(_li!=NULL)*_li=_of->cur_link;
+              return trimmed_duration;
+            }
+          }
+        }
+        /*Don't grab another page yet.
+          This one might have more packets, or might have buffered data now.*/
+        continue;
+      }
+    }
+    /*Suck in another page.*/
+    ret=op_fetch_and_process_page(_of,NULL,-1,1,0);
+    if(OP_UNLIKELY(ret==OP_EOF)){
+      if(_li!=NULL)*_li=_of->cur_link;
+      return 0;
+    }
+    if(OP_UNLIKELY(ret<0))return ret;
+  }
+}
+
+/*A generic filter to apply to the decoded audio data.
+  _src is non-const because we will destructively modify the contents of the
+   source buffer that we consume in some cases.*/
+typedef int (*op_read_filter_func)(OggOpusFile *_of,void *_dst,int _dst_sz,
+ op_sample *_src,int _nsamples,int _nchannels);
+
+/*Decode some samples and then apply a custom filter to them.
+  This is used to convert to different output formats.*/
+static int op_filter_read_native(OggOpusFile *_of,void *_dst,int _dst_sz,
+ op_read_filter_func _filter,int *_li){
+  int ret;
+  /*Ensure we have some decoded samples in our buffer.*/
+  ret=op_read_native(_of,NULL,0,_li);
+  /*Now apply the filter to them.*/
+  if(OP_LIKELY(ret>=0)&&OP_LIKELY(_of->ready_state>=OP_INITSET)){
+    int od_buffer_pos;
+    od_buffer_pos=_of->od_buffer_pos;
+    ret=_of->od_buffer_size-od_buffer_pos;
+    if(OP_LIKELY(ret>0)){
+      int nchannels;
+      nchannels=_of->links[_of->seekable?_of->cur_link:0].head.channel_count;
+      ret=(*_filter)(_of,_dst,_dst_sz,
+       _of->od_buffer+nchannels*od_buffer_pos,ret,nchannels);
+      OP_ASSERT(ret>=0);
+      OP_ASSERT(ret<=_of->od_buffer_size-od_buffer_pos);
+      od_buffer_pos+=ret;
+      _of->od_buffer_pos=od_buffer_pos;
+    }
+  }
+  return ret;
+}
+
+#if !defined(OP_FIXED_POINT)||!defined(OP_DISABLE_FLOAT_API)
+
+/*Matrices for downmixing from the supported channel counts to stereo.
+  The matrices with 5 or more channels are normalized to a total volume of 2.0,
+   since most mixes sound too quiet if normalized to 1.0 (as there is generally
+   little volume in the side/rear channels).*/
+static const float OP_STEREO_DOWNMIX[OP_NCHANNELS_MAX-2][OP_NCHANNELS_MAX][2]={
+  /*3.0*/
+  {
+    {0.5858F,0.0F},{0.4142F,0.4142F},{0.0F,0.5858F}
+  },
+  /*quadrophonic*/
+  {
+    {0.4226F,0.0F},{0.0F,0.4226F},{0.366F,0.2114F},{0.2114F,0.336F}
+  },
+  /*5.0*/
+  {
+    {0.651F,0.0F},{0.46F,0.46F},{0.0F,0.651F},{0.5636F,0.3254F},
+    {0.3254F,0.5636F}
+  },
+  /*5.1*/
+  {
+    {0.529F,0.0F},{0.3741F,0.3741F},{0.0F,0.529F},{0.4582F,0.2645F},
+    {0.2645F,0.4582F},{0.3741F,0.3741F}
+  },
+  /*6.1*/
+  {
+    {0.4553F,0.0F},{0.322F,0.322F},{0.0F,0.4553F},{0.3943F,0.2277F},
+    {0.2277F,0.3943F},{0.2788F,0.2788F},{0.322F,0.322F}
+  },
+  /*7.1*/
+  {
+    {0.3886F,0.0F},{0.2748F,0.2748F},{0.0F,0.3886F},{0.3366F,0.1943F},
+    {0.1943F,0.3366F},{0.3366F,0.1943F},{0.1943F,0.3366F},{0.2748F,0.2748F}
+  }
+};
+
+#endif
+
+#if defined(OP_FIXED_POINT)
+
+/*Matrices for downmixing from the supported channel counts to stereo.
+  The matrices with 5 or more channels are normalized to a total volume of 2.0,
+   since most mixes sound too quiet if normalized to 1.0 (as there is generally
+   little volume in the side/rear channels).
+  Hence we keep the coefficients in Q14, so the downmix values won't overflow a
+   32-bit number.*/
+static const opus_int16 OP_STEREO_DOWNMIX_Q14
+ [OP_NCHANNELS_MAX-2][OP_NCHANNELS_MAX][2]={
+  /*3.0*/
+  {
+    {9598,0},{6786,6786},{0,9598}
+  },
+  /*quadrophonic*/
+  {
+    {6924,0},{0,6924},{5996,3464},{3464,5996}
+  },
+  /*5.0*/
+  {
+    {10666,0},{7537,7537},{0,10666},{9234,5331},{5331,9234}
+  },
+  /*5.1*/
+  {
+    {8668,0},{6129,6129},{0,8668},{7507,4335},{4335,7507},{6129,6129}
+  },
+  /*6.1*/
+  {
+    {7459,0},{5275,5275},{0,7459},{6460,3731},{3731,6460},{4568,4568},
+    {5275,5275}
+  },
+  /*7.1*/
+  {
+    {6368,0},{4502,4502},{0,6368},{5515,3183},{3183,5515},{5515,3183},
+    {3183,5515},{4502,4502}
+  }
+};
+
+int op_read(OggOpusFile *_of,opus_int16 *_pcm,int _buf_size,int *_li){
+  return op_read_native(_of,_pcm,_buf_size,_li);
+}
+
+static int op_stereo_filter(OggOpusFile *_of,void *_dst,int _dst_sz,
+ op_sample *_src,int _nsamples,int _nchannels){
+  (void)_of;
+  _nsamples=OP_MIN(_nsamples,_dst_sz>>1);
+  if(_nchannels==2)memcpy(_dst,_src,_nsamples*2*sizeof(*_src));
+  else{
+    opus_int16 *dst;
+    int         i;
+    dst=(opus_int16 *)_dst;
+    if(_nchannels==1){
+      for(i=0;i<_nsamples;i++)dst[2*i+0]=dst[2*i+1]=_src[i];
+    }
+    else{
+      for(i=0;i<_nsamples;i++){
+        opus_int32 l;
+        opus_int32 r;
+        int        ci;
+        l=r=0;
+        for(ci=0;ci<_nchannels;ci++){
+          opus_int32 s;
+          s=_src[_nchannels*i+ci];
+          l+=OP_STEREO_DOWNMIX_Q14[_nchannels-3][ci][0]*s;
+          r+=OP_STEREO_DOWNMIX_Q14[_nchannels-3][ci][1]*s;
+        }
+        /*TODO: For 5 or more channels, we should do soft clipping here.*/
+        dst[2*i+0]=(opus_int16)OP_CLAMP(-32768,l+8192>>14,32767);
+        dst[2*i+1]=(opus_int16)OP_CLAMP(-32768,r+8192>>14,32767);
+      }
+    }
+  }
+  return _nsamples;
+}
+
+int op_read_stereo(OggOpusFile *_of,opus_int16 *_pcm,int _buf_size){
+  return op_filter_read_native(_of,_pcm,_buf_size,op_stereo_filter,NULL);
+}
+
+# if !defined(OP_DISABLE_FLOAT_API)
+
+static int op_short2float_filter(OggOpusFile *_of,void *_dst,int _dst_sz,
+ op_sample *_src,int _nsamples,int _nchannels){
+  float *dst;
+  int    i;
+  (void)_of;
+  dst=(float *)_dst;
+  if(OP_UNLIKELY(_nsamples*_nchannels>_dst_sz))_nsamples=_dst_sz/_nchannels;
+  _dst_sz=_nsamples*_nchannels;
+  for(i=0;i<_dst_sz;i++)dst[i]=(1.0F/32768)*_src[i];
+  return _nsamples;
+}
+
+int op_read_float(OggOpusFile *_of,float *_pcm,int _buf_size,int *_li){
+  return op_filter_read_native(_of,_pcm,_buf_size,op_short2float_filter,_li);
+}
+
+static int op_short2float_stereo_filter(OggOpusFile *_of,
+ void *_dst,int _dst_sz,op_sample *_src,int _nsamples,int _nchannels){
+  float *dst;
+  int    i;
+  dst=(float *)_dst;
+  _nsamples=OP_MIN(_nsamples,_dst_sz>>1);
+  if(_nchannels==1){
+    _nsamples=op_short2float_filter(_of,dst,_nsamples,_src,_nsamples,1);
+    for(i=_nsamples;i-->0;)dst[2*i+0]=dst[2*i+1]=dst[i];
+  }
+  else if(_nchannels<5){
+    /*For 3 or 4 channels, we can downmix in fixed point without risk of
+       clipping.*/
+    if(_nchannels>2){
+      _nsamples=op_stereo_filter(_of,_src,_nsamples*2,
+       _src,_nsamples,_nchannels);
+    }
+    return op_short2float_filter(_of,dst,_dst_sz,_src,_nsamples,2);
+  }
+  else{
+    /*For 5 or more channels, we convert to floats and then downmix (so that we
+       don't risk clipping).*/
+    for(i=0;i<_nsamples;i++){
+      float l;
+      float r;
+      int   ci;
+      l=r=0;
+      for(ci=0;ci<_nchannels;ci++){
+        float s;
+        s=(1.0F/32768)*_src[_nchannels*i+ci];
+        l+=OP_STEREO_DOWNMIX[_nchannels-3][ci][0]*s;
+        r+=OP_STEREO_DOWNMIX[_nchannels-3][ci][1]*s;
+      }
+      dst[2*i+0]=l;
+      dst[2*i+1]=r;
+    }
+  }
+  return _nsamples;
+}
+
+int op_read_float_stereo(OggOpusFile *_of,float *_pcm,int _buf_size){
+  return op_filter_read_native(_of,_pcm,_buf_size,
+   op_short2float_stereo_filter,NULL);
+}
+
+# endif
+
+#else
+
+# if defined(OP_HAVE_LRINTF)
+#  include <math.h>
+#  define op_float2int(_x) (lrintf(_x))
+# else
+#  define op_float2int(_x) ((int)((_x)+((_x)<0?-0.5F:0.5F)))
+# endif
+
+/*The dithering code here is adapted from opusdec, part of opus-tools.
+  It was originally written by Greg Maxwell.*/
+
+static opus_uint32 op_rand(opus_uint32 _seed){
+  return _seed*96314165+907633515&0xFFFFFFFFU;
+}
+
+/*This implements 16-bit quantization with full triangular dither and IIR noise
+   shaping.
+  The noise shaping filters were designed by Sebastian Gesemann, and are based
+   on the LAME ATH curves with flattening to limit their peak gain to 20 dB.
+  Everyone else's noise shaping filters are mildly crazy.
+  The 48 kHz version of this filter is just a warped version of the 44.1 kHz
+   filter and probably could be improved by shifting the HF shelf up in
+   frequency a little bit, since 48 kHz has a bit more room and being more
+   conservative against bat-ears is probably more important than more noise
+   suppression.
+  This process can increase the peak level of the signal (in theory by the peak
+   error of 1.5 +20 dB, though that is unobservably rare).
+  To avoid clipping, the signal is attenuated by a couple thousandths of a dB.
+  Initially, the approach taken here was to only attenuate by the 99.9th
+   percentile, making clipping rare but not impossible (like SoX), but the
+   limited gain of the filter means that the worst case was only two
+   thousandths of a dB more, so this just uses the worst case.
+  The attenuation is probably also helpful to prevent clipping in the DAC
+   reconstruction filters or downstream resampling, in any case.*/
+
+# define OP_GAIN (32753.0F)
+
+# define OP_PRNG_GAIN (1.0F/0xFFFFFFFF)
+
+/*48 kHz noise shaping filter, sd=2.34.*/
+
+static const float OP_FCOEF_B[4]={
+  2.2374F,-0.7339F,-0.1251F,-0.6033F
+};
+
+static const float OP_FCOEF_A[4]={
+  0.9030F,0.0116F,-0.5853F,-0.2571F
+};
+
+static int op_float2short_filter(OggOpusFile *_of,void *_dst,int _dst_sz,
+ float *_src,int _nsamples,int _nchannels){
+  opus_int16 *dst;
+  int         ci;
+  int         i;
+  dst=(opus_int16 *)_dst;
+  if(OP_UNLIKELY(_nsamples*_nchannels>_dst_sz))_nsamples=_dst_sz/_nchannels;
+# if defined(OP_SOFT_CLIP)
+  if(_of->state_channel_count!=_nchannels){
+    for(ci=0;ci<_nchannels;ci++)_of->clip_state[ci]=0;
+  }
+  opus_pcm_soft_clip(_src,_nsamples,_nchannels,_of->clip_state);
+# endif
+  if(_of->dither_disabled){
+    for(i=0;i<_nchannels*_nsamples;i++){
+      dst[i]=op_float2int(OP_CLAMP(-32768,32768.0F*_src[i],32767));
+    }
+  }
+  else{
+    opus_uint32 seed;
+    int         mute;
+    seed=_of->dither_seed;
+    mute=_of->dither_mute;
+    if(_of->state_channel_count!=_nchannels)mute=65;
+    /*In order to avoid replacing digital silence with quiet dither noise, we
+       mute if the output has been silent for a while.*/
+    if(mute>64)memset(_of->dither_a,0,sizeof(*_of->dither_a)*4*_nchannels);
+    for(i=0;i<_nsamples;i++){
+      int silent;
+      silent=1;
+      for(ci=0;ci<_nchannels;ci++){
+        float r;
+        float s;
+        float err;
+        int   si;
+        int   j;
+        s=_src[_nchannels*i+ci];
+        silent&=s==0;
+        s*=OP_GAIN;
+        err=0;
+        for(j=0;j<4;j++){
+          err+=OP_FCOEF_B[j]*_of->dither_b[ci*4+j]
+           -OP_FCOEF_A[j]*_of->dither_a[ci*4+j];
+        }
+        for(j=3;j-->0;)_of->dither_a[ci*4+j+1]=_of->dither_a[ci*4+j];
+        for(j=3;j-->0;)_of->dither_b[ci*4+j+1]=_of->dither_b[ci*4+j];
+        _of->dither_a[ci*4]=err;
+        s-=err;
+        if(mute>16)r=0;
+        else{
+          seed=op_rand(seed);
+          r=seed*OP_PRNG_GAIN;
+          seed=op_rand(seed);
+          r-=seed*OP_PRNG_GAIN;
+        }
+        /*Clamp in float out of paranoia that the input will be > 96 dBFS and
+           wrap if the integer is clamped.*/
+        si=op_float2int(OP_CLAMP(-32768,s+r,32767));
+        dst[_nchannels*i+ci]=(opus_int16)si;
+        /*Including clipping in the noise shaping is generally disastrous: the
+           futile effort to restore the clipped energy results in more clipping.
+          However, small amounts---at the level which could normally be created
+           by dither and rounding---are harmless and can even reduce clipping
+           somewhat due to the clipping sometimes reducing the dither + rounding
+           error.*/
+        _of->dither_b[ci*4]=mute>16?0:OP_CLAMP(-1.5F,si-s,1.5F);
+      }
+      mute++;
+      if(!silent)mute=0;
+    }
+    _of->dither_mute=OP_MIN(mute,65);
+    _of->dither_seed=seed;
+  }
+  _of->state_channel_count=_nchannels;
+  return _nsamples;
+}
+
+int op_read(OggOpusFile *_of,opus_int16 *_pcm,int _buf_size,int *_li){
+  return op_filter_read_native(_of,_pcm,_buf_size,op_float2short_filter,_li);
+}
+
+int op_read_float(OggOpusFile *_of,float *_pcm,int _buf_size,int *_li){
+  _of->state_channel_count=0;
+  return op_read_native(_of,_pcm,_buf_size,_li);
+}
+
+static int op_stereo_filter(OggOpusFile *_of,void *_dst,int _dst_sz,
+ op_sample *_src,int _nsamples,int _nchannels){
+  (void)_of;
+  _nsamples=OP_MIN(_nsamples,_dst_sz>>1);
+  if(_nchannels==2)memcpy(_dst,_src,_nsamples*2*sizeof(*_src));
+  else{
+    float *dst;
+    int    i;
+    dst=(float *)_dst;
+    if(_nchannels==1){
+      for(i=0;i<_nsamples;i++)dst[2*i+0]=dst[2*i+1]=_src[i];
+    }
+    else{
+      for(i=0;i<_nsamples;i++){
+        float l;
+        float r;
+        int   ci;
+        l=r=0;
+        for(ci=0;ci<_nchannels;ci++){
+          l+=OP_STEREO_DOWNMIX[_nchannels-3][ci][0]*_src[_nchannels*i+ci];
+          r+=OP_STEREO_DOWNMIX[_nchannels-3][ci][1]*_src[_nchannels*i+ci];
+        }
+        dst[2*i+0]=l;
+        dst[2*i+1]=r;
+      }
+    }
+  }
+  return _nsamples;
+}
+
+static int op_float2short_stereo_filter(OggOpusFile *_of,
+ void *_dst,int _dst_sz,op_sample *_src,int _nsamples,int _nchannels){
+  opus_int16 *dst;
+  dst=(opus_int16 *)_dst;
+  if(_nchannels==1){
+    int i;
+    _nsamples=op_float2short_filter(_of,dst,_dst_sz>>1,_src,_nsamples,1);
+    for(i=_nsamples;i-->0;)dst[2*i+0]=dst[2*i+1]=dst[i];
+  }
+  else{
+    if(_nchannels>2){
+      _nsamples=OP_MIN(_nsamples,_dst_sz>>1);
+      _nsamples=op_stereo_filter(_of,_src,_nsamples*2,
+       _src,_nsamples,_nchannels);
+    }
+    _nsamples=op_float2short_filter(_of,dst,_dst_sz,_src,_nsamples,2);
+  }
+  return _nsamples;
+}
+
+int op_read_stereo(OggOpusFile *_of,opus_int16 *_pcm,int _buf_size){
+  return op_filter_read_native(_of,_pcm,_buf_size,
+   op_float2short_stereo_filter,NULL);
+}
+
+int op_read_float_stereo(OggOpusFile *_of,float *_pcm,int _buf_size){
+  _of->state_channel_count=0;
+  return op_filter_read_native(_of,_pcm,_buf_size,op_stereo_filter,NULL);
+}
+
+#endif
\ No newline at end of file
diff --git a/opusfile/opusfile.h b/opusfile/opusfile.h
new file mode 100644
index 0000000..1e753fa
--- /dev/null
+++ b/opusfile/opusfile.h
@@ -0,0 +1,2164 @@
+/********************************************************************
+ *                                                                  *
+ * THIS FILE IS PART OF THE libopusfile SOFTWARE CODEC SOURCE CODE. *
+ * USE, DISTRIBUTION AND REPRODUCTION OF THIS LIBRARY SOURCE IS     *
+ * GOVERNED BY A BSD-STYLE SOURCE LICENSE INCLUDED WITH THIS SOURCE *
+ * IN 'COPYING'. PLEASE READ THESE TERMS BEFORE DISTRIBUTING.       *
+ *                                                                  *
+ * THE libopusfile SOURCE CODE IS (C) COPYRIGHT 1994-2012           *
+ * by the Xiph.Org Foundation and contributors http://www.xiph.org/ *
+ *                                                                  *
+ ********************************************************************
+
+ function: stdio-based convenience library for opening/seeking/decoding
+ last mod: $Id: vorbisfile.h 17182 2010-04-29 03:48:32Z xiphmont $
+
+ ********************************************************************/
+#if !defined(_opusfile_h)
+# define _opusfile_h (1)
+
+/**\mainpage
+   \section Introduction
+
+   This is the documentation for the <tt>libopusfile</tt> C API.
+
+   The <tt>libopusfile</tt> package provides a convenient high-level API for
+    decoding and basic manipulation of all Ogg Opus audio streams.
+   <tt>libopusfile</tt> is implemented as a layer on top of Xiph.Org's
+    reference
+    <tt><a href="https://www.xiph.org/ogg/doc/libogg/reference.html">libogg</a></tt>
+    and
+    <tt><a href="https://mf4.xiph.org/jenkins/view/opus/job/opus/ws/doc/html/index.html">libopus</a></tt>
+    libraries.
+
+   <tt>libopusfile</tt> provides several sets of built-in routines for
+    file/stream access, and may also use custom stream I/O routines provided by
+    the embedded environment.
+   There are built-in I/O routines provided for ANSI-compliant
+    <code>stdio</code> (<code>FILE *</code>), memory buffers, and URLs
+    (including <file:> URLs, plus optionally <http:> and <https:> URLs).
+
+   \section Organization
+
+   The main API is divided into several sections:
+   - \ref stream_open_close
+   - \ref stream_info
+   - \ref stream_decoding
+   - \ref stream_seeking
+
+   Several additional sections are not tied to the main API.
+   - \ref stream_callbacks
+   - \ref header_info
+   - \ref error_codes
+
+   \section Overview
+
+   The <tt>libopusfile</tt> API always decodes files to 48&nbsp;kHz.
+   The original sample rate is not preserved by the lossy compression, though
+    it is stored in the header to allow you to resample to it after decoding
+    (the <tt>libopusfile</tt> API does not currently provide a resampler,
+    but the
+    <a href="http://www.speex.org/docs/manual/speex-manual/node7.html#SECTION00760000000000000000">the
+    Speex resampler</a> is a good choice if you need one).
+   In general, if you are playing back the audio, you should leave it at
+    48&nbsp;kHz, provided your audio hardware supports it.
+   When decoding to a file, it may be worth resampling back to the original
+    sample rate, so as not to surprise users who might not expect the sample
+    rate to change after encoding to Opus and decoding.
+
+   Opus files can contain anywhere from 1 to 255 channels of audio.
+   The channel mappings for up to 8 channels are the same as the
+    <a href="http://www.xiph.org/vorbis/doc/Vorbis_I_spec.html#x1-800004.3.9">Vorbis
+    mappings</a>.
+   A special stereo API can convert everything to 2 channels, making it simple
+    to support multichannel files in an application which only has stereo
+    output.
+   Although the <tt>libopusfile</tt> ABI provides support for the theoretical
+    maximum number of channels, the current implementation does not support
+    files with more than 8 channels, as they do not have well-defined channel
+    mappings.
+
+   Like all Ogg files, Opus files may be "chained".
+   That is, multiple Opus files may be combined into a single, longer file just
+    by concatenating the original files.
+   This is commonly done in internet radio streaming, as it allows the title
+    and artist to be updated each time the song changes, since each link in the
+    chain includes its own set of metadata.
+
+   <tt>libopusfile</tt> fully supports chained files.
+   It will decode the first Opus stream found in each link of a chained file
+    (ignoring any other streams that might be concurrently multiplexed with it,
+    such as a video stream).
+
+   The channel count can also change between links.
+   If your application is not prepared to deal with this, it can use the stereo
+    API to ensure the audio from all links will always get decoded into a
+    common format.
+   Since <tt>libopusfile</tt> always decodes to 48&nbsp;kHz, you do not have to
+    worry about the sample rate changing between links (as was possible with
+    Vorbis).
+   This makes application support for chained files with <tt>libopusfile</tt>
+    very easy.*/
+
+# if defined(__cplusplus)
+extern "C" {
+# endif
+
+# include <stdarg.h>
+# include <stdio.h>
+# include "../libogg/ogg.h"
+# include <opus/opus_multistream.h>
+
+/**@cond PRIVATE*/
+
+/*Enable special features for gcc and gcc-compatible compilers.*/
+# if !defined(OP_GNUC_PREREQ)
+#  if defined(__GNUC__)&&defined(__GNUC_MINOR__)
+#   define OP_GNUC_PREREQ(_maj,_min) \
+ ((__GNUC__<<16)+__GNUC_MINOR__>=((_maj)<<16)+(_min))
+#  else
+#   define OP_GNUC_PREREQ(_maj,_min) 0
+#  endif
+# endif
+
+# if OP_GNUC_PREREQ(4,0)
+#  pragma GCC visibility push(default)
+# endif
+
+typedef struct OpusHead          OpusHead;
+typedef struct OpusTags          OpusTags;
+typedef struct OpusPictureTag    OpusPictureTag;
+typedef struct OpusServerInfo    OpusServerInfo;
+typedef struct OpusFileCallbacks OpusFileCallbacks;
+typedef struct OggOpusFile       OggOpusFile;
+
+/*Warning attributes for libopusfile functions.*/
+# if OP_GNUC_PREREQ(3,4)
+#  define OP_WARN_UNUSED_RESULT __attribute__((__warn_unused_result__))
+# else
+#  define OP_WARN_UNUSED_RESULT
+# endif
+# if OP_GNUC_PREREQ(3,4)
+#  define OP_ARG_NONNULL(_x) __attribute__((__nonnull__(_x)))
+# else
+#  define OP_ARG_NONNULL(_x)
+# endif
+
+/**@endcond*/
+
+/**\defgroup error_codes Error Codes*/
+/*@{*/
+/**\name List of possible error codes
+   Many of the functions in this library return a negative error code when a
+    function fails.
+   This list provides a brief explanation of the common errors.
+   See each individual function for more details on what a specific error code
+    means in that context.*/
+/*@{*/
+
+/**A request did not succeed.*/
+#define OP_FALSE         (-1)
+/*Currently not used externally.*/
+#define OP_EOF           (-2)
+/**There was a hole in the page sequence numbers (e.g., a page was corrupt or
+    missing).*/
+#define OP_HOLE          (-3)
+/**An underlying read, seek, or tell operation failed when it should have
+    succeeded.*/
+#define OP_EREAD         (-128)
+/**A <code>NULL</code> pointer was passed where one was unexpected, or an
+    internal memory allocation failed, or an internal library error was
+    encountered.*/
+#define OP_EFAULT        (-129)
+/**The stream used a feature that is not implemented, such as an unsupported
+    channel family.*/
+#define OP_EIMPL         (-130)
+/**One or more parameters to a function were invalid.*/
+#define OP_EINVAL        (-131)
+/**A purported Ogg Opus stream did not begin with an Ogg page, a purported
+    header packet did not start with one of the required strings, "OpusHead" or
+    "OpusTags", or a link in a chained file was encountered that did not
+    contain any logical Opus streams.*/
+#define OP_ENOTFORMAT    (-132)
+/**A required header packet was not properly formatted, contained illegal
+    values, or was missing altogether.*/
+#define OP_EBADHEADER    (-133)
+/**The ID header contained an unrecognized version number.*/
+#define OP_EVERSION      (-134)
+/*Currently not used at all.*/
+#define OP_ENOTAUDIO     (-135)
+/**An audio packet failed to decode properly.
+   This is usually caused by a multistream Ogg packet where the durations of
+    the individual Opus packets contained in it are not all the same.*/
+#define OP_EBADPACKET    (-136)
+/**We failed to find data we had seen before, or the bitstream structure was
+    sufficiently malformed that seeking to the target destination was
+    impossible.*/
+#define OP_EBADLINK      (-137)
+/**An operation that requires seeking was requested on an unseekable stream.*/
+#define OP_ENOSEEK       (-138)
+/**The first or last granule position of a link failed basic validity checks.*/
+#define OP_EBADTIMESTAMP (-139)
+
+/*@}*/
+/*@}*/
+
+/**\defgroup header_info Header Information*/
+/*@{*/
+
+/**The maximum number of channels in an Ogg Opus stream.*/
+#define OPUS_CHANNEL_COUNT_MAX (255)
+
+/**Ogg Opus bitstream information.
+   This contains the basic playback parameters for a stream, and corresponds to
+    the initial ID header packet of an Ogg Opus stream.*/
+struct OpusHead{
+  /**The Ogg Opus format version, in the range 0...255.
+     The top 4 bits represent a "major" version, and the bottom four bits
+      represent backwards-compatible "minor" revisions.
+     The current specification describes version 1.
+     This library will recognize versions up through 15 as backwards compatible
+      with the current specification.
+     An earlier draft of the specification described a version 0, but the only
+      difference between version 1 and version 0 is that version 0 did
+      not specify the semantics for handling the version field.*/
+  int           version;
+  /**The number of channels, in the range 1...255.*/
+  int           channel_count;
+  /**The number of samples that should be discarded from the beginning of the
+      stream.*/
+  unsigned      pre_skip;
+  /**The sampling rate of the original input.
+     All Opus audio is coded at 48 kHz, and should also be decoded at 48 kHz
+      for playback (unless the target hardware does not support this sampling
+      rate).
+     However, this field may be used to resample the audio back to the original
+      sampling rate, for example, when saving the output to a file.*/
+  opus_uint32   input_sample_rate;
+  /**The gain to apply to the decoded output, in dB, as a Q8 value in the range
+      -32768...32767.
+     The <tt>libopusfile</tt> API will automatically apply this gain to the
+      decoded output before returning it, scaling it by
+      <code>pow(10,output_gain/(20.0*256))</code>.
+     You can adjust this behavior with op_set_gain_offset().*/
+  int           output_gain;
+  /**The channel mapping family, in the range 0...255.
+     Channel mapping family 0 covers mono or stereo in a single stream.
+     Channel mapping family 1 covers 1 to 8 channels in one or more streams,
+      using the Vorbis speaker assignments.
+     Channel mapping family 255 covers 1 to 255 channels in one or more
+      streams, but without any defined speaker assignment.*/
+  int           mapping_family;
+  /**The number of Opus streams in each Ogg packet, in the range 1...255.*/
+  int           stream_count;
+  /**The number of coupled Opus streams in each Ogg packet, in the range
+      0...127.
+     This must satisfy <code>0 <= coupled_count <= stream_count</code> and
+      <code>coupled_count + stream_count <= 255</code>.
+     The coupled streams appear first, before all uncoupled streams, in an Ogg
+      Opus packet.*/
+  int           coupled_count;
+  /**The mapping from coded stream channels to output channels.
+     Let <code>index=mapping[k]</code> be the value for channel <code>k</code>.
+     If <code>index<2*coupled_count</code>, then it refers to the left channel
+      from stream <code>(index/2)</code> if even, and the right channel from
+      stream <code>(index/2)</code> if odd.
+     Otherwise, it refers to the output of the uncoupled stream
+      <code>(index-coupled_count)</code>.*/
+  unsigned char mapping[OPUS_CHANNEL_COUNT_MAX];
+};
+
+/**The metadata from an Ogg Opus stream.
+
+   This structure holds the in-stream metadata corresponding to the 'comment'
+    header packet of an Ogg Opus stream.
+   The comment header is meant to be used much like someone jotting a quick
+    note on the label of a CD.
+   It should be a short, to the point text note that can be more than a couple
+    words, but not more than a short paragraph.
+
+   The metadata is stored as a series of (tag, value) pairs, in length-encoded
+    string vectors, using the same format as Vorbis (without the final "framing
+    bit"), Theora, and Speex, except for the packet header.
+   The first occurrence of the '=' character delimits the tag and value.
+   A particular tag may occur more than once, and order is significant.
+   The character set encoding for the strings is always UTF-8, but the tag
+    names are limited to ASCII, and treated as case-insensitive.
+   See <a href="http://www.xiph.org/vorbis/doc/v-comment.html">the Vorbis
+    comment header specification</a> for details.
+
+   In filling in this structure, <tt>libopusfile</tt> will null-terminate the
+    #user_comments strings for safety.
+   However, the bitstream format itself treats them as 8-bit clean vectors,
+    possibly containing NUL characters, so the #comment_lengths array should be
+    treated as their authoritative length.
+
+   This structure is binary and source-compatible with a
+    <code>vorbis_comment</code>, and pointers to it may be freely cast to
+    <code>vorbis_comment</code> pointers, and vice versa.
+   It is provided as a separate type to avoid introducing a compile-time
+    dependency on the libvorbis headers.*/
+struct OpusTags{
+  /**The array of comment string vectors.*/
+  char **user_comments;
+  /**An array of the corresponding length of each vector, in bytes.*/
+  int   *comment_lengths;
+  /**The total number of comment streams.*/
+  int    comments;
+  /**The null-terminated vendor string.
+     This identifies the software used to encode the stream.*/
+  char  *vendor;
+};
+
+/**\name Picture tag image formats*/
+/*@{*/
+
+/**The MIME type was not recognized, or the image data did not match the
+    declared MIME type.*/
+#define OP_PIC_FORMAT_UNKNOWN (-1)
+/**The MIME type indicates the image data is really a URL.*/
+#define OP_PIC_FORMAT_URL     (0)
+/**The image is a JPEG.*/
+#define OP_PIC_FORMAT_JPEG    (1)
+/**The image is a PNG.*/
+#define OP_PIC_FORMAT_PNG     (2)
+/**The image is a GIF.*/
+#define OP_PIC_FORMAT_GIF     (3)
+
+/*@}*/
+
+/**The contents of a METADATA_BLOCK_PICTURE tag.*/
+struct OpusPictureTag{
+  /**The picture type according to the ID3v2 APIC frame:
+     <ol start="0">
+     <li>Other</li>
+     <li>32x32 pixels 'file icon' (PNG only)</li>
+     <li>Other file icon</li>
+     <li>Cover (front)</li>
+     <li>Cover (back)</li>
+     <li>Leaflet page</li>
+     <li>Media (e.g. label side of CD)</li>
+     <li>Lead artist/lead performer/soloist</li>
+     <li>Artist/performer</li>
+     <li>Conductor</li>
+     <li>Band/Orchestra</li>
+     <li>Composer</li>
+     <li>Lyricist/text writer</li>
+     <li>Recording Location</li>
+     <li>During recording</li>
+     <li>During performance</li>
+     <li>Movie/video screen capture</li>
+     <li>A bright colored fish</li>
+     <li>Illustration</li>
+     <li>Band/artist logotype</li>
+     <li>Publisher/Studio logotype</li>
+     </ol>
+     Others are reserved and should not be used.
+     There may only be one each of picture type 1 and 2 in a file.*/
+  opus_int32     type;
+  /**The MIME type of the picture, in printable ASCII characters 0x20-0x7E.
+     The MIME type may also be <code>"-->"</code> to signify that the data part
+      is a URL pointing to the picture instead of the picture data itself.
+     In this case, a terminating NUL is appended to the URL string in #data,
+      but #data_length is set to the length of the string excluding that
+      terminating NUL.*/
+  char          *mime_type;
+  /**The description of the picture, in UTF-8.*/
+  char          *description;
+  /**The width of the picture in pixels.*/
+  opus_uint32    width;
+  /**The height of the picture in pixels.*/
+  opus_uint32    height;
+  /**The color depth of the picture in bits-per-pixel (<em>not</em>
+      bits-per-channel).*/
+  opus_uint32    depth;
+  /**For indexed-color pictures (e.g., GIF), the number of colors used, or 0
+      for non-indexed pictures.*/
+  opus_uint32    colors;
+  /**The length of the picture data in bytes.*/
+  opus_uint32    data_length;
+  /**The binary picture data.*/
+  unsigned char *data;
+  /**The format of the picture data, if known.
+     One of
+     <ul>
+     <li>#OP_PIC_FORMAT_UNKNOWN,</li>
+     <li>#OP_PIC_FORMAT_URL,</li>
+     <li>#OP_PIC_FORMAT_JPEG,</li>
+     <li>#OP_PIC_FORMAT_PNG, or</li>
+     <li>#OP_PIC_FORMAT_GIF.</li>
+     </ul>*/
+  int            format;
+};
+
+/**\name Functions for manipulating header data
+
+   These functions manipulate the #OpusHead and #OpusTags structures,
+    which describe the audio parameters and tag-value metadata, respectively.
+   These can be used to query the headers returned by <tt>libopusfile</tt>, or
+    to parse Opus headers from sources other than an Ogg Opus stream, provided
+    they use the same format.*/
+/*@{*/
+
+/**Parses the contents of the ID header packet of an Ogg Opus stream.
+   \param[out] _head Returns the contents of the parsed packet.
+                     The contents of this structure are untouched on error.
+                     This may be <code>NULL</code> to merely test the header
+                      for validity.
+   \param[in]  _data The contents of the ID header packet.
+   \param      _len  The number of bytes of data in the ID header packet.
+   \return 0 on success or a negative value on error.
+   \retval #OP_ENOTFORMAT If the data does not start with the "OpusHead"
+                           string.
+   \retval #OP_EVERSION   If the version field signaled a version this library
+                           does not know how to parse.
+   \retval #OP_EIMPL      If the channel mapping family was 255, which general
+                           purpose players should not attempt to play.
+   \retval #OP_EBADHEADER If the contents of the packet otherwise violate the
+                           Ogg Opus specification:
+                          <ul>
+                           <li>Insufficient data,</li>
+                           <li>Too much data for the known minor versions,</li>
+                           <li>An unrecognized channel mapping family,</li>
+                           <li>Zero channels or too many channels,</li>
+                           <li>Zero coded streams,</li>
+                           <li>Too many coupled streams, or</li>
+                           <li>An invalid channel mapping index.</li>
+                          </ul>*/
+OP_WARN_UNUSED_RESULT int opus_head_parse(OpusHead *_head,
+ const unsigned char *_data,size_t _len) OP_ARG_NONNULL(2);
+
+/**Converts a granule position to a sample offset for a given Ogg Opus stream.
+   The sample offset is simply <code>_gp-_head->pre_skip</code>.
+   Granule position values smaller than OpusHead#pre_skip correspond to audio
+    that should never be played, and thus have no associated sample offset.
+   This function returns -1 for such values.
+   This function also correctly handles extremely large granule positions,
+    which may have wrapped around to a negative number when stored in a signed
+    ogg_int64_t value.
+   \param _head The #OpusHead information from the ID header of the stream.
+   \param _gp   The granule position to convert.
+   \return The sample offset associated with the given granule position
+            (counting at a 48 kHz sampling rate), or the special value -1 on
+            error (i.e., the granule position was smaller than the pre-skip
+            amount).*/
+ogg_int64_t opus_granule_sample(const OpusHead *_head,ogg_int64_t _gp)
+ OP_ARG_NONNULL(1);
+
+/**Parses the contents of the 'comment' header packet of an Ogg Opus stream.
+   \param[out] _tags An uninitialized #OpusTags structure.
+                     This returns the contents of the parsed packet.
+                     The contents of this structure are untouched on error.
+                     This may be <code>NULL</code> to merely test the header
+                      for validity.
+   \param[in]  _data The contents of the 'comment' header packet.
+   \param      _len  The number of bytes of data in the 'info' header packet.
+   \retval 0              Success.
+   \retval #OP_ENOTFORMAT If the data does not start with the "OpusTags"
+                           string.
+   \retval #OP_EBADHEADER If the contents of the packet otherwise violate the
+                           Ogg Opus specification.
+   \retval #OP_EFAULT     If there wasn't enough memory to store the tags.*/
+OP_WARN_UNUSED_RESULT int opus_tags_parse(OpusTags *_tags,
+ const unsigned char *_data,size_t _len) OP_ARG_NONNULL(2);
+
+/**Performs a deep copy of an #OpusTags structure.
+   \param _dst The #OpusTags structure to copy into.
+               If this function fails, the contents of this structure remain
+                untouched.
+   \param _src The #OpusTags structure to copy from.
+   \retval 0          Success.
+   \retval #OP_EFAULT If there wasn't enough memory to copy the tags.*/
+int opus_tags_copy(OpusTags *_dst,const OpusTags *_src) OP_ARG_NONNULL(1);
+
+/**Initializes an #OpusTags structure.
+   This should be called on a freshly allocated #OpusTags structure before
+    attempting to use it.
+   \param _tags The #OpusTags structure to initialize.*/
+void opus_tags_init(OpusTags *_tags) OP_ARG_NONNULL(1);
+
+/**Add a (tag, value) pair to an initialized #OpusTags structure.
+   \note Neither opus_tags_add() nor opus_tags_add_comment() support values
+    containing embedded NULs, although the bitstream format does support them.
+   To add such tags, you will need to manipulate the #OpusTags structure
+    directly.
+   \param _tags  The #OpusTags structure to add the (tag, value) pair to.
+   \param _tag   A NUL-terminated, case-insensitive, ASCII string containing
+                  the tag to add (without an '=' character).
+   \param _value A NUL-terminated UTF-8 containing the corresponding value.
+   \return 0 on success, or a negative value on failure.
+   \retval #OP_EFAULT An internal memory allocation failed.*/
+int opus_tags_add(OpusTags *_tags,const char *_tag,const char *_value)
+ OP_ARG_NONNULL(1) OP_ARG_NONNULL(2) OP_ARG_NONNULL(3);
+
+/**Add a comment to an initialized #OpusTags structure.
+   \note Neither opus_tags_add_comment() nor opus_tags_add() support comments
+    containing embedded NULs, although the bitstream format does support them.
+   To add such tags, you will need to manipulate the #OpusTags structure
+    directly.
+   \param _tags    The #OpusTags structure to add the comment to.
+   \param _comment A NUL-terminated UTF-8 string containing the comment in
+                    "TAG=value" form.
+   \return 0 on success, or a negative value on failure.
+   \retval #OP_EFAULT An internal memory allocation failed.*/
+int opus_tags_add_comment(OpusTags *_tags,const char *_comment)
+ OP_ARG_NONNULL(1) OP_ARG_NONNULL(2);
+
+/**Replace the binary suffix data at the end of the packet (if any).
+   \param _tags An initialized #OpusTags structure.
+   \param _data A buffer of binary data to append after the encoded user
+                 comments.
+                The least significant bit of the first byte of this data must
+                 be set (to ensure the data is preserved by other editors).
+   \param _len  The number of bytes of binary data to append.
+                This may be zero to remove any existing binary suffix data.
+   \return 0 on success, or a negative value on error.
+   \retval #OP_EINVAL \a _len was negative, or \a _len was positive but
+                       \a _data was <code>NULL</code> or the least significant
+                       bit of the first byte was not set.
+   \retval #OP_EFAULT An internal memory allocation failed.*/
+int opus_tags_set_binary_suffix(OpusTags *_tags,
+ const unsigned char *_data,int _len) OP_ARG_NONNULL(1);
+
+/**Look up a comment value by its tag.
+   \param _tags  An initialized #OpusTags structure.
+   \param _tag   The tag to look up.
+   \param _count The instance of the tag.
+                 The same tag can appear multiple times, each with a distinct
+                  value, so an index is required to retrieve them all.
+                 The order in which these values appear is significant and
+                  should be preserved.
+                 Use opus_tags_query_count() to get the legal range for the
+                  \a _count parameter.
+   \return A pointer to the queried tag's value.
+           This points directly to data in the #OpusTags structure.
+           It should not be modified or freed by the application, and
+            modifications to the structure may invalidate the pointer.
+   \retval NULL If no matching tag is found.*/
+const char *opus_tags_query(const OpusTags *_tags,const char *_tag,int _count)
+ OP_ARG_NONNULL(1) OP_ARG_NONNULL(2);
+
+/**Look up the number of instances of a tag.
+   Call this first when querying for a specific tag and then iterate over the
+    number of instances with separate calls to opus_tags_query() to retrieve
+    all the values for that tag in order.
+   \param _tags An initialized #OpusTags structure.
+   \param _tag  The tag to look up.
+   \return The number of instances of this particular tag.*/
+int opus_tags_query_count(const OpusTags *_tags,const char *_tag)
+ OP_ARG_NONNULL(1) OP_ARG_NONNULL(2);
+
+/**Retrieve the binary suffix data at the end of the packet (if any).
+   \param      _tags An initialized #OpusTags structure.
+   \param[out] _len  Returns the number of bytes of binary suffix data returned.
+   \return A pointer to the binary suffix data, or <code>NULL</code> if none
+            was present.*/
+const unsigned char *opus_tags_get_binary_suffix(const OpusTags *_tags,
+ int *_len) OP_ARG_NONNULL(1) OP_ARG_NONNULL(2);
+
+/**Get the album gain from an R128_ALBUM_GAIN tag, if one was specified.
+   This searches for the first R128_ALBUM_GAIN tag with a valid signed,
+    16-bit decimal integer value and returns the value.
+   This routine is exposed merely for convenience for applications which wish
+    to do something special with the album gain (i.e., display it).
+   If you simply wish to apply the album gain instead of the header gain, you
+    can use op_set_gain_offset() with an #OP_ALBUM_GAIN type and no offset.
+   \param      _tags    An initialized #OpusTags structure.
+   \param[out] _gain_q8 The album gain, in 1/256ths of a dB.
+                        This will lie in the range [-32768,32767], and should
+                         be applied in <em>addition</em> to the header gain.
+                        On error, no value is returned, and the previous
+                         contents remain unchanged.
+   \return 0 on success, or a negative value on error.
+   \retval #OP_FALSE There was no album gain available in the given tags.*/
+int opus_tags_get_album_gain(const OpusTags *_tags,int *_gain_q8)
+ OP_ARG_NONNULL(1) OP_ARG_NONNULL(2);
+
+/**Get the track gain from an R128_TRACK_GAIN tag, if one was specified.
+   This searches for the first R128_TRACK_GAIN tag with a valid signed,
+    16-bit decimal integer value and returns the value.
+   This routine is exposed merely for convenience for applications which wish
+    to do something special with the track gain (i.e., display it).
+   If you simply wish to apply the track gain instead of the header gain, you
+    can use op_set_gain_offset() with an #OP_TRACK_GAIN type and no offset.
+   \param      _tags    An initialized #OpusTags structure.
+   \param[out] _gain_q8 The track gain, in 1/256ths of a dB.
+                        This will lie in the range [-32768,32767], and should
+                         be applied in <em>addition</em> to the header gain.
+                        On error, no value is returned, and the previous
+                         contents remain unchanged.
+   \return 0 on success, or a negative value on error.
+   \retval #OP_FALSE There was no track gain available in the given tags.*/
+int opus_tags_get_track_gain(const OpusTags *_tags,int *_gain_q8)
+ OP_ARG_NONNULL(1) OP_ARG_NONNULL(2);
+
+/**Clears the #OpusTags structure.
+   This should be called on an #OpusTags structure after it is no longer
+    needed.
+   It will free all memory used by the structure members.
+   \param _tags The #OpusTags structure to clear.*/
+void opus_tags_clear(OpusTags *_tags) OP_ARG_NONNULL(1);
+
+/**Check if \a _comment is an instance of a \a _tag_name tag.
+   \see opus_tagncompare
+   \param _tag_name A NUL-terminated, case-insensitive, ASCII string containing
+                     the name of the tag to check for (without the terminating
+                     '=' character).
+   \param _comment  The comment string to check.
+   \return An integer less than, equal to, or greater than zero if \a _comment
+            is found respectively, to be less than, to match, or be greater
+            than a "tag=value" string whose tag matches \a _tag_name.*/
+int opus_tagcompare(const char *_tag_name,const char *_comment);
+
+/**Check if \a _comment is an instance of a \a _tag_name tag.
+   This version is slightly more efficient than opus_tagcompare() if the length
+    of the tag name is already known (e.g., because it is a constant).
+   \see opus_tagcompare
+   \param _tag_name A case-insensitive ASCII string containing the name of the
+                     tag to check for (without the terminating '=' character).
+   \param _tag_len  The number of characters in the tag name.
+                    This must be non-negative.
+   \param _comment  The comment string to check.
+   \return An integer less than, equal to, or greater than zero if \a _comment
+            is found respectively, to be less than, to match, or be greater
+            than a "tag=value" string whose tag matches the first \a _tag_len
+            characters of \a _tag_name.*/
+int opus_tagncompare(const char *_tag_name,int _tag_len,const char *_comment);
+
+/**Parse a single METADATA_BLOCK_PICTURE tag.
+   This decodes the BASE64-encoded content of the tag and returns a structure
+    with the MIME type, description, image parameters (if known), and the
+    compressed image data.
+   If the MIME type indicates the presence of an image format we recognize
+    (JPEG, PNG, or GIF) and the actual image data contains the magic signature
+    associated with that format, then the OpusPictureTag::format field will be
+    set to the corresponding format.
+   This is provided as a convenience to avoid requiring applications to parse
+    the MIME type and/or do their own format detection for the commonly used
+    formats.
+   In this case, we also attempt to extract the image parameters directly from
+    the image data (overriding any that were present in the tag, which the
+    specification says applications are not meant to rely on).
+   The application must still provide its own support for actually decoding the
+    image data and, if applicable, retrieving that data from URLs.
+   \param[out] _pic Returns the parsed picture data.
+                    No sanitation is done on the type, MIME type, or
+                     description fields, so these might return invalid values.
+                    The contents of this structure are left unmodified on
+                     failure.
+   \param      _tag The METADATA_BLOCK_PICTURE tag contents.
+                    The leading "METADATA_BLOCK_PICTURE=" portion is optional,
+                     to allow the function to be used on either directly on the
+                     values in OpusTags::user_comments or on the return value
+                     of opus_tags_query().
+   \return 0 on success or a negative value on error.
+   \retval #OP_ENOTFORMAT The METADATA_BLOCK_PICTURE contents were not valid.
+   \retval #OP_EFAULT     There was not enough memory to store the picture tag
+                           contents.*/
+OP_WARN_UNUSED_RESULT int opus_picture_tag_parse(OpusPictureTag *_pic,
+ const char *_tag) OP_ARG_NONNULL(1) OP_ARG_NONNULL(2);
+
+/**Initializes an #OpusPictureTag structure.
+   This should be called on a freshly allocated #OpusPictureTag structure
+    before attempting to use it.
+   \param _pic The #OpusPictureTag structure to initialize.*/
+void opus_picture_tag_init(OpusPictureTag *_pic) OP_ARG_NONNULL(1);
+
+/**Clears the #OpusPictureTag structure.
+   This should be called on an #OpusPictureTag structure after it is no longer
+    needed.
+   It will free all memory used by the structure members.
+   \param _pic The #OpusPictureTag structure to clear.*/
+void opus_picture_tag_clear(OpusPictureTag *_pic) OP_ARG_NONNULL(1);
+
+/*@}*/
+
+/*@}*/
+
+/**\defgroup url_options URL Reading Options*/
+/*@{*/
+/**\name URL reading options
+   Options for op_url_stream_create() and associated functions.
+   These allow you to provide proxy configuration parameters, skip SSL
+    certificate checks, etc.
+   Options are processed in order, and if the same option is passed multiple
+    times, only the value specified by the last occurrence has an effect
+    (unless otherwise specified).
+   They may be expanded in the future.*/
+/*@{*/
+
+/**@cond PRIVATE*/
+
+/*These are the raw numbers used to define the request codes.
+  They should not be used directly.*/
+#define OP_SSL_SKIP_CERTIFICATE_CHECK_REQUEST (6464)
+#define OP_HTTP_PROXY_HOST_REQUEST            (6528)
+#define OP_HTTP_PROXY_PORT_REQUEST            (6592)
+#define OP_HTTP_PROXY_USER_REQUEST            (6656)
+#define OP_HTTP_PROXY_PASS_REQUEST            (6720)
+#define OP_GET_SERVER_INFO_REQUEST            (6784)
+
+#define OP_URL_OPT(_request) ((_request)+(char *)0)
+
+/*These macros trigger compilation errors or warnings if the wrong types are
+   provided to one of the URL options.*/
+#define OP_CHECK_INT(_x) ((void)((_x)==(opus_int32)0),(opus_int32)(_x))
+#define OP_CHECK_CONST_CHAR_PTR(_x) ((_x)+((_x)-(const char *)(_x)))
+#define OP_CHECK_SERVER_INFO_PTR(_x) ((_x)+((_x)-(OpusServerInfo *)(_x)))
+
+/**@endcond*/
+
+/**HTTP/Shoutcast/Icecast server information associated with a URL.*/
+struct OpusServerInfo{
+  /**The name of the server (icy-name/ice-name).
+     This is <code>NULL</code> if there was no <code>icy-name</code> or
+      <code>ice-name</code> header.*/
+  char        *name;
+  /**A short description of the server (icy-description/ice-description).
+     This is <code>NULL</code> if there was no <code>icy-description</code> or
+      <code>ice-description</code> header.*/
+  char        *description;
+  /**The genre the server falls under (icy-genre/ice-genre).
+     This is <code>NULL</code> if there was no <code>icy-genre</code> or
+      <code>ice-genre</code> header.*/
+  char        *genre;
+  /**The homepage for the server (icy-url/ice-url).
+     This is <code>NULL</code> if there was no <code>icy-url</code> or
+      <code>ice-url</code> header.*/
+  char        *url;
+  /**The software used by the origin server (Server).
+     This is <code>NULL</code> if there was no <code>Server</code> header.*/
+  char        *server;
+  /**The media type of the entity sent to the recepient (Content-Type).
+     This is <code>NULL</code> if there was no <code>Content-Type</code>
+      header.*/
+  char        *content_type;
+  /**The nominal stream bitrate in kbps (icy-br/ice-bitrate).
+     This is <code>-1</code> if there was no <code>icy-br</code> or
+      <code>ice-bitrate</code> header.*/
+  opus_int32   bitrate_kbps;
+  /**Flag indicating whether the server is public (<code>1</code>) or not
+      (<code>0</code>) (icy-pub/ice-public).
+     This is <code>-1</code> if there was no <code>icy-pub</code> or
+      <code>ice-public</code> header.*/
+  int          is_public;
+  /**Flag indicating whether the server is using HTTPS instead of HTTP.
+     This is <code>0</code> unless HTTPS is being used.
+     This may not match the protocol used in the original URL if there were
+      redirections.*/
+  int          is_ssl;
+};
+
+/**Initializes an #OpusServerInfo structure.
+   All fields are set as if the corresponding header was not available.
+   \param _info The #OpusServerInfo structure to initialize.
+   \note If you use this function, you must link against <tt>libopusurl</tt>.*/
+void opus_server_info_init(OpusServerInfo *_info) OP_ARG_NONNULL(1);
+
+/**Clears the #OpusServerInfo structure.
+   This should be called on an #OpusServerInfo structure after it is no longer
+    needed.
+   It will free all memory used by the structure members.
+   \param _info The #OpusServerInfo structure to clear.
+   \note If you use this function, you must link against <tt>libopusurl</tt>.*/
+void opus_server_info_clear(OpusServerInfo *_info) OP_ARG_NONNULL(1);
+
+/**Skip the certificate check when connecting via TLS/SSL (https).
+   \param _b <code>opus_int32</code>: Whether or not to skip the certificate
+              check.
+             The check will be skipped if \a _b is non-zero, and will not be
+              skipped if \a _b is zero.
+   \hideinitializer*/
+#define OP_SSL_SKIP_CERTIFICATE_CHECK(_b) \
+ OP_URL_OPT(OP_SSL_SKIP_CERTIFICATE_CHECK_REQUEST),OP_CHECK_INT(_b)
+
+/**Proxy connections through the given host.
+   If no port is specified via #OP_HTTP_PROXY_PORT, the port number defaults
+    to 8080 (http-alt).
+   All proxy parameters are ignored for non-http and non-https URLs.
+   \param _host <code>const char *</code>: The proxy server hostname.
+                This may be <code>NULL</code> to disable the use of a proxy
+                 server.
+   \hideinitializer*/
+#define OP_HTTP_PROXY_HOST(_host) \
+ OP_URL_OPT(OP_HTTP_PROXY_HOST_REQUEST),OP_CHECK_CONST_CHAR_PTR(_host)
+
+/**Use the given port when proxying connections.
+   This option only has an effect if #OP_HTTP_PROXY_HOST is specified with a
+    non-<code>NULL</code> \a _host.
+   If this option is not provided, the proxy port number defaults to 8080
+    (http-alt).
+   All proxy parameters are ignored for non-http and non-https URLs.
+   \param _port <code>opus_int32</code>: The proxy server port.
+                This must be in the range 0...65535 (inclusive), or the
+                 URL function this is passed to will fail.
+   \hideinitializer*/
+#define OP_HTTP_PROXY_PORT(_port) \
+ OP_URL_OPT(OP_HTTP_PROXY_PORT_REQUEST),OP_CHECK_INT(_port)
+
+/**Use the given user name for authentication when proxying connections.
+   All proxy parameters are ignored for non-http and non-https URLs.
+   \param _user const char *: The proxy server user name.
+                              This may be <code>NULL</code> to disable proxy
+                               authentication.
+                              A non-<code>NULL</code> value only has an effect
+                               if #OP_HTTP_PROXY_HOST and #OP_HTTP_PROXY_PASS
+                               are also specified with non-<code>NULL</code>
+                               arguments.
+   \hideinitializer*/
+#define OP_HTTP_PROXY_USER(_user) \
+ OP_URL_OPT(OP_HTTP_PROXY_USER_REQUEST),OP_CHECK_CONST_CHAR_PTR(_user)
+
+/**Use the given password for authentication when proxying connections.
+   All proxy parameters are ignored for non-http and non-https URLs.
+   \param _pass const char *: The proxy server password.
+                              This may be <code>NULL</code> to disable proxy
+                               authentication.
+                              A non-<code>NULL</code> value only has an effect
+                               if #OP_HTTP_PROXY_HOST and #OP_HTTP_PROXY_USER
+                               are also specified with non-<code>NULL</code>
+                               arguments.
+   \hideinitializer*/
+#define OP_HTTP_PROXY_PASS(_pass) \
+ OP_URL_OPT(OP_HTTP_PROXY_PASS_REQUEST),OP_CHECK_CONST_CHAR_PTR(_pass)
+
+/**Parse information about the streaming server (if any) and return it.
+   Very little validation is done.
+   In particular, OpusServerInfo::url may not be a valid URL,
+    OpusServerInfo::bitrate_kbps may not really be in kbps, and
+    OpusServerInfo::content_type may not be a valid MIME type.
+   The character set of the string fields is not specified anywhere, and should
+    not be assumed to be valid UTF-8.
+   \param _info OpusServerInfo *: Returns information about the server.
+                                  If there is any error opening the stream, the
+                                   contents of this structure remain
+                                   unmodified.
+                                  On success, fills in the structure with the
+                                   server information that was available, if
+                                   any.
+                                  After a successful return, the contents of
+                                   this structure should be freed by calling
+                                   opus_server_info_clear().
+   \hideinitializer*/
+#define OP_GET_SERVER_INFO(_info) \
+ OP_URL_OPT(OP_GET_SERVER_INFO_REQUEST),OP_CHECK_SERVER_INFO_PTR(_info)
+
+/*@}*/
+/*@}*/
+
+/**\defgroup stream_callbacks Abstract Stream Reading Interface*/
+/*@{*/
+/**\name Functions for reading from streams
+   These functions define the interface used to read from and seek in a stream
+    of data.
+   A stream does not need to implement seeking, but the decoder will not be
+    able to seek if it does not do so.
+   These functions also include some convenience routines for working with
+    standard <code>FILE</code> pointers, complete streams stored in a single
+    block of memory, or URLs.*/
+/*@{*/
+
+/**Reads up to \a _nbytes bytes of data from \a _stream.
+   \param      _stream The stream to read from.
+   \param[out] _ptr    The buffer to store the data in.
+   \param      _nbytes The maximum number of bytes to read.
+                       This function may return fewer, though it will not
+                        return zero unless it reaches end-of-file.
+   \return The number of bytes successfully read, or a negative value on
+            error.*/
+typedef int (*op_read_func)(void *_stream,unsigned char *_ptr,int _nbytes);
+
+/**Sets the position indicator for \a _stream.
+   The new position, measured in bytes, is obtained by adding \a _offset
+    bytes to the position specified by \a _whence.
+   If \a _whence is set to <code>SEEK_SET</code>, <code>SEEK_CUR</code>, or
+    <code>SEEK_END</code>, the offset is relative to the start of the stream,
+    the current position indicator, or end-of-file, respectively.
+   \retval 0  Success.
+   \retval -1 Seeking is not supported or an error occurred.
+              <code>errno</code> need not be set.*/
+typedef int (*op_seek_func)(void *_stream,opus_int64 _offset,int _whence);
+
+/**Obtains the current value of the position indicator for \a _stream.
+   \return The current position indicator.*/
+typedef opus_int64 (*op_tell_func)(void *_stream);
+
+/**Closes the underlying stream.
+   \retval 0   Success.
+   \retval EOF An error occurred.
+               <code>errno</code> need not be set.*/
+typedef int (*op_close_func)(void *_stream);
+
+/**The callbacks used to access non-<code>FILE</code> stream resources.
+   The function prototypes are basically the same as for the stdio functions
+    <code>fread()</code>, <code>fseek()</code>, <code>ftell()</code>, and
+    <code>fclose()</code>.
+   The differences are that the <code>FILE *</code> arguments have been
+    replaced with a <code>void *</code>, which is to be used as a pointer to
+    whatever internal data these functions might need, that #seek and #tell
+    take and return 64-bit offsets, and that #seek <em>must</em> return -1 if
+    the stream is unseekable.*/
+struct OpusFileCallbacks{
+  /**Used to read data from the stream.
+     This must not be <code>NULL</code>.*/
+  op_read_func  read;
+  /**Used to seek in the stream.
+     This may be <code>NULL</code> if seeking is not implemented.*/
+  op_seek_func  seek;
+  /**Used to return the current read position in the stream.
+     This may be <code>NULL</code> if seeking is not implemented.*/
+  op_tell_func  tell;
+  /**Used to close the stream when the decoder is freed.
+     This may be <code>NULL</code> to leave the stream open.*/
+  op_close_func close;
+};
+
+/**Opens a stream with <code>fopen()</code> and fills in a set of callbacks
+    that can be used to access it.
+   This is useful to avoid writing your own portable 64-bit seeking wrappers,
+    and also avoids cross-module linking issues on Windows, where a
+    <code>FILE *</code> must be accessed by routines defined in the same module
+    that opened it.
+   \param[out] _cb   The callbacks to use for this file.
+                     If there is an error opening the file, nothing will be
+                      filled in here.
+   \param      _path The path to the file to open.
+                     On Windows, this string must be UTF-8 (to allow access to
+                      files whose names cannot be represented in the current
+                      MBCS code page).
+                     All other systems use the native character encoding.
+   \param      _mode The mode to open the file in.
+   \return A stream handle to use with the callbacks, or <code>NULL</code> on
+            error.*/
+OP_WARN_UNUSED_RESULT void *op_fopen(OpusFileCallbacks *_cb,
+ const char *_path,const char *_mode) OP_ARG_NONNULL(1) OP_ARG_NONNULL(2)
+ OP_ARG_NONNULL(3);
+
+/**Opens a stream with <code>fdopen()</code> and fills in a set of callbacks
+    that can be used to access it.
+   This is useful to avoid writing your own portable 64-bit seeking wrappers,
+    and also avoids cross-module linking issues on Windows, where a
+    <code>FILE *</code> must be accessed by routines defined in the same module
+    that opened it.
+   \param[out] _cb   The callbacks to use for this file.
+                     If there is an error opening the file, nothing will be
+                      filled in here.
+   \param      _fd   The file descriptor to open.
+   \param      _mode The mode to open the file in.
+   \return A stream handle to use with the callbacks, or <code>NULL</code> on
+            error.*/
+OP_WARN_UNUSED_RESULT void *op_fdopen(OpusFileCallbacks *_cb,
+ int _fd,const char *_mode) OP_ARG_NONNULL(1) OP_ARG_NONNULL(3);
+
+/**Opens a stream with <code>freopen()</code> and fills in a set of callbacks
+    that can be used to access it.
+   This is useful to avoid writing your own portable 64-bit seeking wrappers,
+    and also avoids cross-module linking issues on Windows, where a
+    <code>FILE *</code> must be accessed by routines defined in the same module
+    that opened it.
+   \param[out] _cb     The callbacks to use for this file.
+                       If there is an error opening the file, nothing will be
+                        filled in here.
+   \param      _path   The path to the file to open.
+                       On Windows, this string must be UTF-8 (to allow access
+                        to files whose names cannot be represented in the
+                        current MBCS code page).
+                       All other systems use the native character encoding.
+   \param      _mode   The mode to open the file in.
+   \param      _stream A stream previously returned by op_fopen(), op_fdopen(),
+                        or op_freopen().
+   \return A stream handle to use with the callbacks, or <code>NULL</code> on
+            error.*/
+OP_WARN_UNUSED_RESULT void *op_freopen(OpusFileCallbacks *_cb,
+ const char *_path,const char *_mode,void *_stream) OP_ARG_NONNULL(1)
+ OP_ARG_NONNULL(2) OP_ARG_NONNULL(3) OP_ARG_NONNULL(4);
+
+/**Creates a stream that reads from the given block of memory.
+   This block of memory must contain the complete stream to decode.
+   This is useful for caching small streams (e.g., sound effects) in RAM.
+   \param[out] _cb   The callbacks to use for this stream.
+                     If there is an error creating the stream, nothing will be
+                      filled in here.
+   \param      _data The block of memory to read from.
+   \param      _size The size of the block of memory.
+   \return A stream handle to use with the callbacks, or <code>NULL</code> on
+            error.*/
+OP_WARN_UNUSED_RESULT void *op_mem_stream_create(OpusFileCallbacks *_cb,
+ const unsigned char *_data,size_t _size) OP_ARG_NONNULL(1);
+
+/**Creates a stream that reads from the given URL.
+   This function behaves identically to op_url_stream_create(), except that it
+    takes a va_list instead of a variable number of arguments.
+   It does not call the <code>va_end</code> macro, and because it invokes the
+    <code>va_arg</code> macro, the value of \a _ap is undefined after the call.
+   \note If you use this function, you must link against <tt>libopusurl</tt>.
+   \param[out]    _cb  The callbacks to use for this stream.
+                       If there is an error creating the stream, nothing will
+                        be filled in here.
+   \param         _url The URL to read from.
+                       Currently only the <file:>, <http:>, and <https:>
+                        schemes are supported.
+                       Both <http:> and <https:> may be disabled at compile
+                        time, in which case opening such URLs will always fail.
+                       Currently this only supports URIs.
+                       IRIs should be converted to UTF-8 and URL-escaped, with
+                        internationalized domain names encoded in punycode,
+                        before passing them to this function.
+   \param[in,out] _ap  A list of the \ref url_options "optional flags" to use.
+                       This is a variable-length list of options terminated
+                        with <code>NULL</code>.
+   \return A stream handle to use with the callbacks, or <code>NULL</code> on
+            error.*/
+OP_WARN_UNUSED_RESULT void *op_url_stream_vcreate(OpusFileCallbacks *_cb,
+ const char *_url,va_list _ap) OP_ARG_NONNULL(1) OP_ARG_NONNULL(2);
+
+/**Creates a stream that reads from the given URL.
+   \note If you use this function, you must link against <tt>libopusurl</tt>.
+   \param[out] _cb  The callbacks to use for this stream.
+                    If there is an error creating the stream, nothing will be
+                     filled in here.
+   \param      _url The URL to read from.
+                    Currently only the <file:>, <http:>, and <https:> schemes
+                     are supported.
+                    Both <http:> and <https:> may be disabled at compile time,
+                     in which case opening such URLs will always fail.
+                    Currently this only supports URIs.
+                    IRIs should be converted to UTF-8 and URL-escaped, with
+                     internationalized domain names encoded in punycode, before
+                     passing them to this function.
+   \param      ...  The \ref url_options "optional flags" to use.
+                    This is a variable-length list of options terminated with
+                     <code>NULL</code>.
+   \return A stream handle to use with the callbacks, or <code>NULL</code> on
+            error.*/
+OP_WARN_UNUSED_RESULT void *op_url_stream_create(OpusFileCallbacks *_cb,
+ const char *_url,...) OP_ARG_NONNULL(1) OP_ARG_NONNULL(2);
+
+/*@}*/
+/*@}*/
+
+/**\defgroup stream_open_close Opening and Closing*/
+/*@{*/
+/**\name Functions for opening and closing streams
+
+   These functions allow you to test a stream to see if it is Opus, open it,
+    and close it.
+   Several flavors are provided for each of the built-in stream types, plus a
+    more general version which takes a set of application-provided callbacks.*/
+/*@{*/
+
+/**Test to see if this is an Opus stream.
+   For good results, you will need at least 57 bytes (for a pure Opus-only
+    stream).
+   Something like 512 bytes will give more reliable results for multiplexed
+    streams.
+   This function is meant to be a quick-rejection filter.
+   Its purpose is not to guarantee that a stream is a valid Opus stream, but to
+    ensure that it looks enough like Opus that it isn't going to be recognized
+    as some other format (except possibly an Opus stream that is also
+    multiplexed with other codecs, such as video).
+   \param[out] _head     The parsed ID header contents.
+                         You may pass <code>NULL</code> if you do not need
+                          this information.
+                         If the function fails, the contents of this structure
+                          remain untouched.
+   \param _initial_data  An initial buffer of data from the start of the
+                          stream.
+   \param _initial_bytes The number of bytes in \a _initial_data.
+   \return 0 if the data appears to be Opus, or a negative value on error.
+   \retval #OP_FALSE      There was not enough data to tell if this was an Opus
+                           stream or not.
+   \retval #OP_EFAULT     An internal memory allocation failed.
+   \retval #OP_EIMPL      The stream used a feature that is not implemented,
+                           such as an unsupported channel family.
+   \retval #OP_ENOTFORMAT If the data did not contain a recognizable ID
+                           header for an Opus stream.
+   \retval #OP_EVERSION   If the version field signaled a version this library
+                           does not know how to parse.
+   \retval #OP_EBADHEADER The ID header was not properly formatted or contained
+                           illegal values.*/
+int op_test(OpusHead *_head,
+ const unsigned char *_initial_data,size_t _initial_bytes);
+
+/**Open a stream from the given file path.
+   \param      _path  The path to the file to open.
+   \param[out] _error Returns 0 on success, or a failure code on error.
+                      You may pass in <code>NULL</code> if you don't want the
+                       failure code.
+                      The failure code will be #OP_EFAULT if the file could not
+                       be opened, or one of the other failure codes from
+                       op_open_callbacks() otherwise.
+   \return A freshly opened \c OggOpusFile, or <code>NULL</code> on error.*/
+OP_WARN_UNUSED_RESULT OggOpusFile *op_open_file(const char *_path,int *_error)
+ OP_ARG_NONNULL(1);
+
+/**Open a stream from a memory buffer.
+   \param      _data  The memory buffer to open.
+   \param      _size  The number of bytes in the buffer.
+   \param[out] _error Returns 0 on success, or a failure code on error.
+                      You may pass in <code>NULL</code> if you don't want the
+                       failure code.
+                      See op_open_callbacks() for a full list of failure codes.
+   \return A freshly opened \c OggOpusFile, or <code>NULL</code> on error.*/
+OP_WARN_UNUSED_RESULT OggOpusFile *op_open_memory(const unsigned char *_data,
+ size_t _size,int *_error);
+
+/**Open a stream from a URL.
+   This function behaves identically to op_open_url(), except that it
+    takes a va_list instead of a variable number of arguments.
+   It does not call the <code>va_end</code> macro, and because it invokes the
+    <code>va_arg</code> macro, the value of \a _ap is undefined after the call.
+   \note If you use this function, you must link against <tt>libopusurl</tt>.
+   \param         _url   The URL to open.
+                         Currently only the <file:>, <http:>, and <https:>
+                          schemes are supported.
+                         Both <http:> and <https:> may be disabled at compile
+                          time, in which case opening such URLs will always
+                          fail.
+                         Currently this only supports URIs.
+                         IRIs should be converted to UTF-8 and URL-escaped,
+                          with internationalized domain names encoded in
+                          punycode, before passing them to this function.
+   \param[out]    _error Returns 0 on success, or a failure code on error.
+                         You may pass in <code>NULL</code> if you don't want
+                          the failure code.
+                         See op_open_callbacks() for a full list of failure
+                          codes.
+   \param[in,out] _ap    A list of the \ref url_options "optional flags" to
+                          use.
+                         This is a variable-length list of options terminated
+                          with <code>NULL</code>.
+   \return A freshly opened \c OggOpusFile, or <code>NULL</code> on error.*/
+OP_WARN_UNUSED_RESULT OggOpusFile *op_vopen_url(const char *_url,
+ int *_error,va_list _ap) OP_ARG_NONNULL(1);
+
+/**Open a stream from a URL.
+   \note If you use this function, you must link against <tt>libopusurl</tt>.
+   \param      _url   The URL to open.
+                      Currently only the <file:>, <http:>, and <https:> schemes
+                       are supported.
+                      Both <http:> and <https:> may be disabled at compile
+                       time, in which case opening such URLs will always fail.
+                      Currently this only supports URIs.
+                      IRIs should be converted to UTF-8 and URL-escaped, with
+                       internationalized domain names encoded in punycode,
+                       before passing them to this function.
+   \param[out] _error Returns 0 on success, or a failure code on error.
+                      You may pass in <code>NULL</code> if you don't want the
+                       failure code.
+                      See op_open_callbacks() for a full list of failure codes.
+   \param      ...    The \ref url_options "optional flags" to use.
+                      This is a variable-length list of options terminated with
+                       <code>NULL</code>.
+   \return A freshly opened \c OggOpusFile, or <code>NULL</code> on error.*/
+OP_WARN_UNUSED_RESULT OggOpusFile *op_open_url(const char *_url,
+ int *_error,...) OP_ARG_NONNULL(1);
+
+/**Open a stream using the given set of callbacks to access it.
+   \param _stream        The stream to read from (e.g., a <code>FILE *</code>).
+                         This value will be passed verbatim as the first
+                          argument to all of the callbacks.
+   \param _cb            The callbacks with which to access the stream.
+                         <code><a href="#op_read_func">read()</a></code> must
+                          be implemented.
+                         <code><a href="#op_seek_func">seek()</a></code> and
+                          <code><a href="#op_tell_func">tell()</a></code> may
+                          be <code>NULL</code>, or may always return -1 to
+                          indicate a stream is unseekable, but if
+                          <code><a href="#op_seek_func">seek()</a></code> is
+                          implemented and succeeds on a particular stream, then
+                          <code><a href="#op_tell_func">tell()</a></code> must
+                          also.
+                         <code><a href="#op_close_func">close()</a></code> may
+                          be <code>NULL</code>, but if it is not, it will be
+                          called when the \c OggOpusFile is destroyed by
+                          op_free().
+                         It will not be called if op_open_callbacks() fails
+                          with an error.
+   \param _initial_data  An initial buffer of data from the start of the
+                          stream.
+                         Applications can read some number of bytes from the
+                          start of the stream to help identify this as an Opus
+                          stream, and then provide them here to allow the
+                          stream to be opened, even if it is unseekable.
+   \param _initial_bytes The number of bytes in \a _initial_data.
+                         If the stream is seekable, its current position (as
+                          reported by
+                          <code><a href="#opus_tell_func">tell()</a></code>
+                          at the start of this function) must be equal to
+                          \a _initial_bytes.
+                         Otherwise, seeking to absolute positions will
+                          generate inconsistent results.
+   \param[out] _error    Returns 0 on success, or a failure code on error.
+                         You may pass in <code>NULL</code> if you don't want
+                          the failure code.
+                         The failure code will be one of
+                         <dl>
+                           <dt>#OP_EREAD</dt>
+                           <dd>An underlying read, seek, or tell operation
+                            failed when it should have succeeded, or we failed
+                            to find data in the stream we had seen before.</dd>
+                           <dt>#OP_EFAULT</dt>
+                           <dd>There was a memory allocation failure, or an
+                            internal library error.</dd>
+                           <dt>#OP_EIMPL</dt>
+                           <dd>The stream used a feature that is not
+                            implemented, such as an unsupported channel
+                            family.</dd>
+                           <dt>#OP_EINVAL</dt>
+                           <dd><code><a href="#op_seek_func">seek()</a></code>
+                            was implemented and succeeded on this source, but
+                            <code><a href="#op_tell_func">tell()</a></code>
+                            did not, or the starting position indicator was
+                            not equal to \a _initial_bytes.</dd>
+                           <dt>#OP_ENOTFORMAT</dt>
+                           <dd>The stream contained a link that did not have
+                            any logical Opus streams in it.</dd>
+                           <dt>#OP_EBADHEADER</dt>
+                           <dd>A required header packet was not properly
+                            formatted, contained illegal values, or was missing
+                            altogether.</dd>
+                           <dt>#OP_EVERSION</dt>
+                           <dd>An ID header contained an unrecognized version
+                            number.</dd>
+                           <dt>#OP_EBADLINK</dt>
+                           <dd>We failed to find data we had seen before after
+                            seeking.</dd>
+                           <dt>#OP_EBADTIMESTAMP</dt>
+                           <dd>The first or last timestamp in a link failed
+                            basic validity checks.</dd>
+                         </dl>
+   \return A freshly opened \c OggOpusFile, or <code>NULL</code> on error.
+           <tt>libopusfile</tt> does <em>not</em> take ownership of the stream
+            if the call fails.
+           The calling application is responsible for closing the stream if
+            this call returns an error.*/
+OP_WARN_UNUSED_RESULT OggOpusFile *op_open_callbacks(void *_stream,
+ const OpusFileCallbacks *_cb,const unsigned char *_initial_data,
+ size_t _initial_bytes,int *_error) OP_ARG_NONNULL(2);
+
+/**Partially open a stream from the given file path.
+   \see op_test_callbacks
+   \param      _path  The path to the file to open.
+   \param[out] _error Returns 0 on success, or a failure code on error.
+                      You may pass in <code>NULL</code> if you don't want the
+                       failure code.
+                      The failure code will be #OP_EFAULT if the file could not
+                       be opened, or one of the other failure codes from
+                       op_open_callbacks() otherwise.
+   \return A partially opened \c OggOpusFile, or <code>NULL</code> on error.*/
+OP_WARN_UNUSED_RESULT OggOpusFile *op_test_file(const char *_path,int *_error)
+ OP_ARG_NONNULL(1);
+
+/**Partially open a stream from a memory buffer.
+   \see op_test_callbacks
+   \param      _data  The memory buffer to open.
+   \param      _size  The number of bytes in the buffer.
+   \param[out] _error Returns 0 on success, or a failure code on error.
+                      You may pass in <code>NULL</code> if you don't want the
+                       failure code.
+                      See op_open_callbacks() for a full list of failure codes.
+   \return A partially opened \c OggOpusFile, or <code>NULL</code> on error.*/
+OP_WARN_UNUSED_RESULT OggOpusFile *op_test_memory(const unsigned char *_data,
+ size_t _size,int *_error);
+
+/**Partially open a stream from a URL.
+   This function behaves identically to op_test_url(), except that it
+    takes a va_list instead of a variable number of arguments.
+   It does not call the <code>va_end</code> macro, and because it invokes the
+    <code>va_arg</code> macro, the value of \a _ap is undefined after the call.
+   \note If you use this function, you must link against <tt>libopusurl</tt>.
+   \see op_test_url
+   \see op_test_callbacks
+   \param         _url    The URL to open.
+                          Currently only the <file:>, <http:>, and <https:>
+                           schemes are supported.
+                          Both <http:> and <https:> may be disabled at compile
+                           time, in which case opening such URLs will always
+                           fail.
+                          Currently this only supports URIs.
+                          IRIs should be converted to UTF-8 and URL-escaped,
+                           with internationalized domain names encoded in
+                           punycode, before passing them to this function.
+   \param[out]    _error  Returns 0 on success, or a failure code on error.
+                          You may pass in <code>NULL</code> if you don't want
+                           the failure code.
+                          See op_open_callbacks() for a full list of failure
+                           codes.
+   \param[in,out] _ap     A list of the \ref url_options "optional flags" to
+                           use.
+                          This is a variable-length list of options terminated
+                           with <code>NULL</code>.
+   \return A partially opened \c OggOpusFile, or <code>NULL</code> on error.*/
+OP_WARN_UNUSED_RESULT OggOpusFile *op_vtest_url(const char *_url,
+ int *_error,va_list _ap) OP_ARG_NONNULL(1);
+
+/**Partially open a stream from a URL.
+   \note If you use this function, you must link against <tt>libopusurl</tt>.
+   \see op_test_callbacks
+   \param      _url    The URL to open.
+                       Currently only the <file:>, <http:>, and <https:>
+                        schemes are supported.
+                       Both <http:> and <https:> may be disabled at compile
+                        time, in which case opening such URLs will always fail.
+                       Currently this only supports URIs.
+                       IRIs should be converted to UTF-8 and URL-escaped, with
+                        internationalized domain names encoded in punycode,
+                        before passing them to this function.
+   \param[out] _error  Returns 0 on success, or a failure code on error.
+                       You may pass in <code>NULL</code> if you don't want the
+                        failure code.
+                       See op_open_callbacks() for a full list of failure
+                        codes.
+   \param      ...     The \ref url_options "optional flags" to use.
+                       This is a variable-length list of options terminated
+                        with <code>NULL</code>.
+   \return A partially opened \c OggOpusFile, or <code>NULL</code> on error.*/
+OP_WARN_UNUSED_RESULT OggOpusFile *op_test_url(const char *_url,
+ int *_error,...) OP_ARG_NONNULL(1);
+
+/**Partially open a stream using the given set of callbacks to access it.
+   This tests for Opusness and loads the headers for the first link.
+   It does not seek (although it tests for seekability).
+   You can query a partially open stream for the few pieces of basic
+    information returned by op_serialno(), op_channel_count(), op_head(), and
+    op_tags() (but only for the first link).
+   You may also determine if it is seekable via a call to op_seekable().
+   You cannot read audio from the stream, seek, get the size or duration,
+    get information from links other than the first one, or even get the total
+    number of links until you finish opening the stream with op_test_open().
+   If you do not need to do any of these things, you can dispose of it with
+    op_free() instead.
+
+   This function is provided mostly to simplify porting existing code that used
+    <tt>libvorbisfile</tt>.
+   For new code, you are likely better off using op_test() instead, which
+    is less resource-intensive, requires less data to succeed, and imposes a
+    hard limit on the amount of data it examines (important for unseekable
+    streams, where all such data must be buffered until you are sure of the
+    stream type).
+   \param _stream        The stream to read from (e.g., a <code>FILE *</code>).
+                         This value will be passed verbatim as the first
+                          argument to all of the callbacks.
+   \param _cb            The callbacks with which to access the stream.
+                         <code><a href="#op_read_func">read()</a></code> must
+                          be implemented.
+                         <code><a href="#op_seek_func">seek()</a></code> and
+                          <code><a href="#op_tell_func">tell()</a></code> may
+                          be <code>NULL</code>, or may always return -1 to
+                          indicate a stream is unseekable, but if
+                          <code><a href="#op_seek_func">seek()</a></code> is
+                          implemented and succeeds on a particular stream, then
+                          <code><a href="#op_tell_func">tell()</a></code> must
+                          also.
+                         <code><a href="#op_close_func">close()</a></code> may
+                          be <code>NULL</code>, but if it is not, it will be
+                          called when the \c OggOpusFile is destroyed by
+                          op_free().
+                         It will not be called if op_open_callbacks() fails
+                          with an error.
+   \param _initial_data  An initial buffer of data from the start of the
+                          stream.
+                         Applications can read some number of bytes from the
+                          start of the stream to help identify this as an Opus
+                          stream, and then provide them here to allow the
+                          stream to be tested more thoroughly, even if it is
+                          unseekable.
+   \param _initial_bytes The number of bytes in \a _initial_data.
+                         If the stream is seekable, its current position (as
+                          reported by
+                          <code><a href="#opus_tell_func">tell()</a></code>
+                          at the start of this function) must be equal to
+                          \a _initial_bytes.
+                         Otherwise, seeking to absolute positions will
+                          generate inconsistent results.
+   \param[out] _error    Returns 0 on success, or a failure code on error.
+                         You may pass in <code>NULL</code> if you don't want
+                          the failure code.
+                         See op_open_callbacks() for a full list of failure
+                          codes.
+   \return A partially opened \c OggOpusFile, or <code>NULL</code> on error.
+           <tt>libopusfile</tt> does <em>not</em> take ownership of the stream
+            if the call fails.
+           The calling application is responsible for closing the stream if
+            this call returns an error.*/
+OP_WARN_UNUSED_RESULT OggOpusFile *op_test_callbacks(void *_stream,
+ const OpusFileCallbacks *_cb,const unsigned char *_initial_data,
+ size_t _initial_bytes,int *_error) OP_ARG_NONNULL(2);
+
+/**Finish opening a stream partially opened with op_test_callbacks() or one of
+    the associated convenience functions.
+   If this function fails, you are still responsible for freeing the
+    \c OggOpusFile with op_free().
+   \param _of The \c OggOpusFile to finish opening.
+   \return 0 on success, or a negative value on error.
+   \retval #OP_EREAD         An underlying read, seek, or tell operation failed
+                              when it should have succeeded.
+   \retval #OP_EFAULT        There was a memory allocation failure, or an
+                              internal library error.
+   \retval #OP_EIMPL         The stream used a feature that is not implemented,
+                              such as an unsupported channel family.
+   \retval #OP_EINVAL        The stream was not partially opened with
+                              op_test_callbacks() or one of the associated
+                              convenience functions.
+   \retval #OP_ENOTFORMAT    The stream contained a link that did not have any
+                              logical Opus streams in it.
+   \retval #OP_EBADHEADER    A required header packet was not properly
+                              formatted, contained illegal values, or was
+                              missing altogether.
+   \retval #OP_EVERSION      An ID header contained an unrecognized version
+                              number.
+   \retval #OP_EBADLINK      We failed to find data we had seen before after
+                              seeking.
+   \retval #OP_EBADTIMESTAMP The first or last timestamp in a link failed basic
+                              validity checks.*/
+int op_test_open(OggOpusFile *_of) OP_ARG_NONNULL(1);
+
+/**Release all memory used by an \c OggOpusFile.
+   \param _of The \c OggOpusFile to free.*/
+void op_free(OggOpusFile *_of);
+
+/*@}*/
+/*@}*/
+
+/**\defgroup stream_info Stream Information*/
+/*@{*/
+/**\name Functions for obtaining information about streams
+
+   These functions allow you to get basic information about a stream, including
+    seekability, the number of links (for chained streams), plus the size,
+    duration, bitrate, header parameters, and meta information for each link
+    (or, where available, the stream as a whole).
+   Some of these (size, duration) are only available for seekable streams.
+   You can also query the current stream position, link, and playback time,
+    and instantaneous bitrate during playback.
+
+   Some of these functions may be used successfully on the partially open
+    streams returned by op_test_callbacks() or one of the associated
+    convenience functions.
+   Their documention will indicate so explicitly.*/
+/*@{*/
+
+/**Returns whether or not the stream being read is seekable.
+   This is true if
+   <ol>
+   <li>The <code><a href="#op_seek_func">seek()</a></code> and
+    <code><a href="#op_tell_func">tell()</a></code> callbacks are both
+    non-<code>NULL</code>,</li>
+   <li>The <code><a href="#op_seek_func">seek()</a></code> callback was
+    successfully executed at least once, and</li>
+   <li>The <code><a href="#op_tell_func">tell()</a></code> callback was
+    successfully able to report the position indicator afterwards.</li>
+   </ol>
+   This function may be called on partially-opened streams.
+   \param _of The \c OggOpusFile whose seekable status is to be returned.
+   \return A non-zero value if seekable, and 0 if unseekable.*/
+int op_seekable(const OggOpusFile *_of) OP_ARG_NONNULL(1);
+
+/**Returns the number of links in this chained stream.
+   This function may be called on partially-opened streams, but it will always
+    return 1.
+   The actual number of links is not known until the stream is fully opened.
+   \param _of The \c OggOpusFile from which to retrieve the link count.
+   \return For fully-open seekable streams, this returns the total number of
+            links in the whole stream, which will be at least 1.
+           For partially-open or unseekable streams, this always returns 1.*/
+int op_link_count(const OggOpusFile *_of) OP_ARG_NONNULL(1);
+
+/**Get the serial number of the given link in a (possibly-chained) Ogg Opus
+    stream.
+   This function may be called on partially-opened streams, but it will always
+    return the serial number of the Opus stream in the first link.
+   \param _of The \c OggOpusFile from which to retrieve the serial number.
+   \param _li The index of the link whose serial number should be retrieved.
+              Use a negative number to get the serial number of the current
+               link.
+   \return The serial number of the given link.
+           If \a _li is greater than the total number of links, this returns
+            the serial number of the last link.
+           If the stream is not seekable, this always returns the serial number
+            of the current link.*/
+opus_uint32 op_serialno(const OggOpusFile *_of,int _li) OP_ARG_NONNULL(1);
+
+/**Get the channel count of the given link in a (possibly-chained) Ogg Opus
+    stream.
+   This is equivalent to <code>op_head(_of,_li)->channel_count</code>, but
+    is provided for convenience.
+   This function may be called on partially-opened streams, but it will always
+    return the channel count of the Opus stream in the first link.
+   \param _of The \c OggOpusFile from which to retrieve the channel count.
+   \param _li The index of the link whose channel count should be retrieved.
+              Use a negative number to get the channel count of the current
+               link.
+   \return The channel count of the given link.
+           If \a _li is greater than the total number of links, this returns
+            the channel count of the last link.
+           If the stream is not seekable, this always returns the channel count
+            of the current link.*/
+int op_channel_count(const OggOpusFile *_of,int _li) OP_ARG_NONNULL(1);
+
+/**Get the total (compressed) size of the stream, or of an individual link in
+    a (possibly-chained) Ogg Opus stream, including all headers and Ogg muxing
+    overhead.
+   \warning If the Opus stream (or link) is concurrently multiplexed with other
+    logical streams (e.g., video), this returns the size of the entire stream
+    (or link), not just the number of bytes in the first logical Opus stream.
+   Returning the latter would require scanning the entire file.
+   \param _of The \c OggOpusFile from which to retrieve the compressed size.
+   \param _li The index of the link whose compressed size should be computed.
+              Use a negative number to get the compressed size of the entire
+               stream.
+   \return The compressed size of the entire stream if \a _li is negative, the
+            compressed size of link \a _li if it is non-negative, or a negative
+            value on error.
+           The compressed size of the entire stream may be smaller than that
+            of the underlying stream if trailing garbage was detected in the
+            file.
+   \retval #OP_EINVAL The stream is not seekable (so we can't know the length),
+                       \a _li wasn't less than the total number of links in
+                       the stream, or the stream was only partially open.*/
+opus_int64 op_raw_total(const OggOpusFile *_of,int _li) OP_ARG_NONNULL(1);
+
+/**Get the total PCM length (number of samples at 48 kHz) of the stream, or of
+    an individual link in a (possibly-chained) Ogg Opus stream.
+   Users looking for <code>op_time_total()</code> should use op_pcm_total()
+    instead.
+   Because timestamps in Opus are fixed at 48 kHz, there is no need for a
+    separate function to convert this to seconds (and leaving it out avoids
+    introducing floating point to the API, for those that wish to avoid it).
+   \param _of The \c OggOpusFile from which to retrieve the PCM offset.
+   \param _li The index of the link whose PCM length should be computed.
+              Use a negative number to get the PCM length of the entire stream.
+   \return The PCM length of the entire stream if \a _li is negative, the PCM
+            length of link \a _li if it is non-negative, or a negative value on
+            error.
+   \retval #OP_EINVAL The stream is not seekable (so we can't know the length),
+                       \a _li wasn't less than the total number of links in
+                       the stream, or the stream was only partially open.*/
+ogg_int64_t op_pcm_total(const OggOpusFile *_of,int _li) OP_ARG_NONNULL(1);
+
+/**Get the ID header information for the given link in a (possibly chained) Ogg
+    Opus stream.
+   This function may be called on partially-opened streams, but it will always
+    return the ID header information of the Opus stream in the first link.
+   \param _of The \c OggOpusFile from which to retrieve the ID header
+               information.
+   \param _li The index of the link whose ID header information should be
+               retrieved.
+              Use a negative number to get the ID header information of the
+               current link.
+              For an unseekable stream, \a _li is ignored, and the ID header
+               information for the current link is always returned, if
+               available.
+   \return The contents of the ID header for the given link.*/
+const OpusHead *op_head(const OggOpusFile *_of,int _li) OP_ARG_NONNULL(1);
+
+/**Get the comment header information for the given link in a (possibly
+    chained) Ogg Opus stream.
+   This function may be called on partially-opened streams, but it will always
+    return the tags from the Opus stream in the first link.
+   \param _of The \c OggOpusFile from which to retrieve the comment header
+               information.
+   \param _li The index of the link whose comment header information should be
+               retrieved.
+              Use a negative number to get the comment header information of
+               the current link.
+              For an unseekable stream, \a _li is ignored, and the comment
+               header information for the current link is always returned, if
+               available.
+   \return The contents of the comment header for the given link, or
+            <code>NULL</code> if this is an unseekable stream that encountered
+            an invalid link.*/
+const OpusTags *op_tags(const OggOpusFile *_of,int _li) OP_ARG_NONNULL(1);
+
+/**Retrieve the index of the current link.
+   This is the link that produced the data most recently read by
+    op_read_float() or its associated functions, or, after a seek, the link
+    that the seek target landed in.
+   Reading more data may advance the link index (even on the first read after a
+    seek).
+   \param _of The \c OggOpusFile from which to retrieve the current link index.
+   \return The index of the current link on success, or a negative value on
+            failure.
+           For seekable streams, this is a number between 0 (inclusive) and the
+            value returned by op_link_count() (exclusive).
+           For unseekable streams, this value starts at 0 and increments by one
+            each time a new link is encountered (even though op_link_count()
+            always returns 1).
+   \retval #OP_EINVAL The stream was only partially open.*/
+int op_current_link(const OggOpusFile *_of) OP_ARG_NONNULL(1);
+
+/**Computes the bitrate of the stream, or of an individual link in a
+    (possibly-chained) Ogg Opus stream.
+   The stream must be seekable to compute the bitrate.
+   For unseekable streams, use op_bitrate_instant() to get periodic estimates.
+   \warning If the Opus stream (or link) is concurrently multiplexed with other
+    logical streams (e.g., video), this uses the size of the entire stream (or
+    link) to compute the bitrate, not just the number of bytes in the first
+    logical Opus stream.
+   Returning the latter requires scanning the entire file, but this may be done
+    by decoding the whole file and calling op_bitrate_instant() once at the
+    end.
+   Install a trivial decoding callback with op_set_decode_callback() if you
+    wish to skip actual decoding during this process.
+   \param _of The \c OggOpusFile from which to retrieve the bitrate.
+   \param _li The index of the link whose bitrate should be computed.
+              Use a negative number to get the bitrate of the whole stream.
+   \return The bitrate on success, or a negative value on error.
+   \retval #OP_EINVAL The stream was only partially open, the stream was not
+                       seekable, or \a _li was larger than the number of
+                       links.*/
+opus_int32 op_bitrate(const OggOpusFile *_of,int _li) OP_ARG_NONNULL(1);
+
+/**Compute the instantaneous bitrate, measured as the ratio of bits to playable
+    samples decoded since a) the last call to op_bitrate_instant(), b) the last
+    seek, or c) the start of playback, whichever was most recent.
+   This will spike somewhat after a seek or at the start/end of a chain
+    boundary, as pre-skip, pre-roll, and end-trimming causes samples to be
+    decoded but not played.
+   \param _of The \c OggOpusFile from which to retrieve the bitrate.
+   \return The bitrate, in bits per second, or a negative value on error.
+   \retval #OP_FALSE  No data has been decoded since any of the events
+                       described above.
+   \retval #OP_EINVAL The stream was only partially open.*/
+opus_int32 op_bitrate_instant(OggOpusFile *_of) OP_ARG_NONNULL(1);
+
+/**Obtain the current value of the position indicator for \a _of.
+   \param _of The \c OggOpusFile from which to retrieve the position indicator.
+   \return The byte position that is currently being read from.
+   \retval #OP_EINVAL The stream was only partially open.*/
+opus_int64 op_raw_tell(const OggOpusFile *_of) OP_ARG_NONNULL(1);
+
+/**Obtain the PCM offset of the next sample to be read.
+   If the stream is not properly timestamped, this might not increment by the
+    proper amount between reads, or even return monotonically increasing
+    values.
+   \param _of The \c OggOpusFile from which to retrieve the PCM offset.
+   \return The PCM offset of the next sample to be read.
+   \retval #OP_EINVAL The stream was only partially open.*/
+ogg_int64_t op_pcm_tell(const OggOpusFile *_of) OP_ARG_NONNULL(1);
+
+/*@}*/
+/*@}*/
+
+/**\defgroup stream_seeking Seeking*/
+/*@{*/
+/**\name Functions for seeking in Opus streams
+
+   These functions let you seek in Opus streams, if the underlying stream
+    support it.
+   Seeking is implemented for all built-in stream I/O routines, though some
+    individual streams may not be seekable (pipes, live HTTP streams, or HTTP
+    streams from a server that does not support <code>Range</code> requests).
+
+   op_raw_seek() is the fastest: it is guaranteed to perform at most one
+    physical seek, but, since the target is a byte position, makes no guarantee
+    how close to a given time it will come.
+   op_pcm_seek() provides sample-accurate seeking.
+   The number of physical seeks it requires is still quite small (often 1 or
+    2, even in highly variable bitrate streams).
+
+   Seeking in Opus requires decoding some pre-roll amount before playback to
+    allow the internal state to converge (as if recovering from packet loss).
+   This is handled internally by <tt>libopusfile</tt>, but means there is
+    little extra overhead for decoding up to the exact position requested
+    (since it must decode some amount of audio anyway).
+   It also means that decoding after seeking may not return exactly the same
+    values as would be obtained by decoding the stream straight through.
+   However, such differences are expected to be smaller than the loss
+    introduced by Opus's lossy compression.*/
+/*@{*/
+
+/**Seek to a byte offset relative to the <b>compressed</b> data.
+   This also scans packets to update the PCM cursor.
+   It will cross a logical bitstream boundary, but only if it can't get any
+    packets out of the tail of the link to which it seeks.
+   \param _of          The \c OggOpusFile in which to seek.
+   \param _byte_offset The byte position to seek to.
+                       This must be between 0 and #op_raw_total(\a _of,\c -1)
+                        (inclusive).
+   \return 0 on success, or a negative error code on failure.
+   \retval #OP_EREAD    The underlying seek operation failed.
+   \retval #OP_EINVAL   The stream was only partially open, or the target was
+                         outside the valid range for the stream.
+   \retval #OP_ENOSEEK  This stream is not seekable.
+   \retval #OP_EBADLINK Failed to initialize a decoder for a stream for an
+                         unknown reason.*/
+int op_raw_seek(OggOpusFile *_of,opus_int64 _byte_offset) OP_ARG_NONNULL(1);
+
+/**Seek to the specified PCM offset, such that decoding will begin at exactly
+    the requested position.
+   \param _of         The \c OggOpusFile in which to seek.
+   \param _pcm_offset The PCM offset to seek to.
+                      This is in samples at 48 kHz relative to the start of the
+                       stream.
+   \return 0 on success, or a negative value on error.
+   \retval #OP_EREAD    An underlying read or seek operation failed.
+   \retval #OP_EINVAL   The stream was only partially open, or the target was
+                         outside the valid range for the stream.
+   \retval #OP_ENOSEEK  This stream is not seekable.
+   \retval #OP_EBADLINK We failed to find data we had seen before, or the
+                         bitstream structure was sufficiently malformed that
+                         seeking to the target destination was impossible.*/
+int op_pcm_seek(OggOpusFile *_of,ogg_int64_t _pcm_offset) OP_ARG_NONNULL(1);
+
+/*@}*/
+/*@}*/
+
+/**\defgroup stream_decoding Decoding*/
+/*@{*/
+/**\name Functions for decoding audio data
+
+   These functions retrieve actual decoded audio data from the stream.
+   The general functions, op_read() and op_read_float() return 16-bit or
+    floating-point output, both using native endian ordering.
+   The number of channels returned can change from link to link in a chained
+    stream.
+   There are special functions, op_read_stereo() and op_read_float_stereo(),
+    which always output two channels, to simplify applications which do not
+    wish to handle multichannel audio.
+   These downmix multichannel files to two channels, so they can always return
+    samples in the same format for every link in a chained file.
+
+   If the rest of your audio processing chain can handle floating point, the
+    floating-point routines should be preferred, as they prevent clipping and
+    other issues which might be avoided entirely if, e.g., you scale down the
+    volume at some other stage.
+   However, if you intend to consume 16-bit samples directly, the conversion in
+    <tt>libopusfile</tt> provides noise-shaping dithering and, if compiled
+    against <tt>libopus</tt>&nbsp;1.1 or later, soft-clipping prevention.
+
+   <tt>libopusfile</tt> can also be configured at compile time to use the
+    fixed-point <tt>libopus</tt> API.
+   If so, <tt>libopusfile</tt>'s floating-point API may also be disabled.
+   In that configuration, nothing in <tt>libopusfile</tt> will use any
+    floating-point operations, to simplify support on devices without an
+    adequate FPU.
+
+   \warning HTTPS streams may be be vulnerable to truncation attacks if you do
+    not check the error return code from op_read_float() or its associated
+    functions.
+   If the remote peer does not close the connection gracefully (with a TLS
+    "close notify" message), these functions will return #OP_EREAD instead of 0
+    when they reach the end of the file.
+   If you are reading from an <https:> URL (particularly if seeking is not
+    supported), you should make sure to check for this error and warn the user
+    appropriately.*/
+/*@{*/
+
+/**Indicates that the decoding callback should produce signed 16-bit
+    native-endian output samples.*/
+#define OP_DEC_FORMAT_SHORT (7008)
+/**Indicates that the decoding callback should produce 32-bit native-endian
+    float samples.*/
+#define OP_DEC_FORMAT_FLOAT (7040)
+
+/**Indicates that the decoding callback did not decode anything, and that
+    <tt>libopusfile</tt> should decode normally instead.*/
+#define OP_DEC_USE_DEFAULT  (6720)
+
+/**Called to decode an Opus packet.
+   This should invoke the functional equivalent of opus_multistream_decode() or
+    opus_multistream_decode_float(), except that it returns 0 on success
+    instead of the number of decoded samples (which is known a priori).
+   \param _ctx       The application-provided callback context.
+   \param _decoder   The decoder to use to decode the packet.
+   \param[out] _pcm  The buffer to decode into.
+                     This will always have enough room for \a _nchannels of
+                      \a _nsamples samples, which should be placed into this
+                      buffer interleaved.
+   \param _op        The packet to decode.
+                     This will always have its granule position set to a valid
+                      value.
+   \param _nsamples  The number of samples expected from the packet.
+   \param _nchannels The number of channels expected from the packet.
+   \param _format    The desired sample output format.
+                     This is either #OP_DEC_FORMAT_SHORT or
+                      #OP_DEC_FORMAT_FLOAT.
+   \param _li        The index of the link from which this packet was decoded.
+   \return A non-negative value on success, or a negative value on error.
+           Any error codes should be the same as those returned by
+            opus_multistream_decode() or opus_multistream_decode_float().
+           Success codes are as follows:
+   \retval 0                   Decoding was successful.
+                               The application has filled the buffer with
+                                exactly <code>\a _nsamples*\a
+                                _nchannels</code> samples in the requested
+                                format.
+   \retval #OP_DEC_USE_DEFAULT No decoding was done.
+                               <tt>libopusfile</tt> should do the decoding
+                                by itself instead.*/
+typedef int (*op_decode_cb_func)(void *_ctx,OpusMSDecoder *_decoder,void *_pcm,
+ const ogg_packet *_op,int _nsamples,int _nchannels,int _format,int _li);
+
+/**Sets the packet decode callback function.
+   If set, this is called once for each packet that needs to be decoded.
+   This can be used by advanced applications to do additional processing on the
+    compressed or uncompressed data.
+   For example, an application might save the final entropy coder state for
+    debugging and testing purposes, or it might apply additional filters
+    before the downmixing, dithering, or soft-clipping performed by
+    <tt>libopusfile</tt>, so long as these filters do not introduce any
+    latency.
+
+   A call to this function is no guarantee that the audio will eventually be
+    delivered to the application.
+   <tt>libopusfile</tt> may discard some or all of the decoded audio data
+    (i.e., at the beginning or end of a link, or after a seek), however the
+    callback is still required to provide all of it.
+   \param _of        The \c OggOpusFile on which to set the decode callback.
+   \param _decode_cb The callback function to call.
+                     This may be <code>NULL</code> to disable calling the
+                      callback.
+   \param _ctx       The application-provided context pointer to pass to the
+                      callback on each call.*/
+void op_set_decode_callback(OggOpusFile *_of,
+ op_decode_cb_func _decode_cb,void *_ctx) OP_ARG_NONNULL(1);
+
+/**Gain offset type that indicates that the provided offset is relative to the
+    header gain.
+   This is the default.*/
+#define OP_HEADER_GAIN   (0)
+
+/**Gain offset type that indicates that the provided offset is relative to the
+    R128_ALBUM_GAIN value (if any), in addition to the header gain.*/
+#define OP_ALBUM_GAIN    (3007)
+
+/**Gain offset type that indicates that the provided offset is relative to the
+    R128_TRACK_GAIN value (if any), in addition to the header gain.*/
+#define OP_TRACK_GAIN    (3008)
+
+/**Gain offset type that indicates that the provided offset should be used as
+    the gain directly, without applying any the header or track gains.*/
+#define OP_ABSOLUTE_GAIN (3009)
+
+/**Sets the gain to be used for decoded output.
+   By default, the gain in the header is applied with no additional offset.
+   The total gain (including header gain and/or track gain, if applicable, and
+    this offset), will be clamped to [-32768,32767]/256 dB.
+   This is more than enough to saturate or underflow 16-bit PCM.
+   \note The new gain will not be applied to any already buffered, decoded
+    output.
+   This means you cannot change it sample-by-sample, as at best it will be
+    updated packet-by-packet.
+   It is meant for setting a target volume level, rather than applying smooth
+    fades, etc.
+   \param _of             The \c OggOpusFile on which to set the gain offset.
+   \param _gain_type      One of #OP_HEADER_GAIN, #OP_ALBUM_GAIN,
+                           #OP_TRACK_GAIN, or #OP_ABSOLUTE_GAIN.
+   \param _gain_offset_q8 The gain offset to apply, in 1/256ths of a dB.
+   \return 0 on success or a negative value on error.
+   \retval #OP_EINVAL The \a _gain_type was unrecognized.*/
+int op_set_gain_offset(OggOpusFile *_of,
+ int _gain_type,opus_int32 _gain_offset_q8) OP_ARG_NONNULL(1);
+
+/**Sets whether or not dithering is enabled for 16-bit decoding.
+   By default, when <tt>libopusfile</tt> is compiled to use floating-point
+    internally, calling op_read() or op_read_stereo() will first decode to
+    float, and then convert to fixed-point using noise-shaping dithering.
+   This flag can be used to disable that dithering.
+   When the application uses op_read_float() or op_read_float_stereo(), or when
+    the library has been compiled to decode directly to fixed point, this flag
+    has no effect.
+   \param _of      The \c OggOpusFile on which to enable or disable dithering.
+   \param _enabled A non-zero value to enable dithering, or 0 to disable it.*/
+void op_set_dither_enabled(OggOpusFile *_of,int _enabled) OP_ARG_NONNULL(1);
+
+/**Reads more samples from the stream.
+   \note Although \a _buf_size must indicate the total number of values that
+    can be stored in \a _pcm, the return value is the number of samples
+    <em>per channel</em>.
+   This is done because
+   <ol>
+   <li>The channel count cannot be known a priori (reading more samples might
+        advance us into the next link, with a different channel count), so
+        \a _buf_size cannot also be in units of samples per channel,</li>
+   <li>Returning the samples per channel matches the <code>libopus</code> API
+        as closely as we're able,</li>
+   <li>Returning the total number of values instead of samples per channel
+        would mean the caller would need a division to compute the samples per
+        channel, and might worry about the possibility of getting back samples
+        for some channels and not others, and</li>
+   <li>This approach is relatively fool-proof: if an application passes too
+        small a value to \a _buf_size, they will simply get fewer samples back,
+        and if they assume the return value is the total number of values, then
+        they will simply read too few (rather than reading too many and going
+        off the end of the buffer).</li>
+   </ol>
+   \param      _of       The \c OggOpusFile from which to read.
+   \param[out] _pcm      A buffer in which to store the output PCM samples, as
+                          signed native-endian 16-bit values at 48&nbsp;kHz
+                          with a nominal range of <code>[-32768,32767)</code>.
+                         Multiple channels are interleaved using the
+                          <a href="http://www.xiph.org/vorbis/doc/Vorbis_I_spec.html#x1-800004.3.9">Vorbis
+                          channel ordering</a>.
+                         This must have room for at least \a _buf_size values.
+   \param      _buf_size The number of values that can be stored in \a _pcm.
+                         It is recommended that this be large enough for at
+                          least 120 ms of data at 48 kHz per channel (5760
+                          values per channel).
+                         Smaller buffers will simply return less data, possibly
+                          consuming more memory to buffer the data internally.
+                         <tt>libopusfile</tt> may return less data than
+                          requested.
+                         If so, there is no guarantee that the remaining data
+                          in \a _pcm will be unmodified.
+   \param[out] _li       The index of the link this data was decoded from.
+                         You may pass <code>NULL</code> if you do not need this
+                          information.
+                         If this function fails (returning a negative value),
+                          this parameter is left unset.
+   \return The number of samples read per channel on success, or a negative
+            value on failure.
+           The channel count can be retrieved on success by calling
+            <code>op_head(_of,*_li)</code>.
+           The number of samples returned may be 0 if the buffer was too small
+            to store even a single sample for all channels, or if end-of-file
+            was reached.
+           The list of possible failure codes follows.
+           Most of them can only be returned by unseekable, chained streams
+            that encounter a new link.
+   \retval #OP_HOLE          There was a hole in the data, and some samples
+                              may have been skipped.
+                             Call this function again to continue decoding
+                              past the hole.
+   \retval #OP_EREAD         An underlying read operation failed.
+                             This may signal a truncation attack from an
+                              <https:> source.
+   \retval #OP_EFAULT        An internal memory allocation failed.
+   \retval #OP_EIMPL         An unseekable stream encountered a new link that
+                              used a feature that is not implemented, such as
+                              an unsupported channel family.
+   \retval #OP_EINVAL        The stream was only partially open.
+   \retval #OP_ENOTFORMAT    An unseekable stream encountered a new link that
+                              did not have any logical Opus streams in it.
+   \retval #OP_EBADHEADER    An unseekable stream encountered a new link with a
+                              required header packet that was not properly
+                              formatted, contained illegal values, or was
+                              missing altogether.
+   \retval #OP_EVERSION      An unseekable stream encountered a new link with
+                              an ID header that contained an unrecognized
+                              version number.
+   \retval #OP_EBADPACKET    Failed to properly decode the next packet.
+   \retval #OP_EBADLINK      We failed to find data we had seen before.
+   \retval #OP_EBADTIMESTAMP An unseekable stream encountered a new link with
+                              a starting timestamp that failed basic validity
+                              checks.*/
+OP_WARN_UNUSED_RESULT int op_read(OggOpusFile *_of,
+ opus_int16 *_pcm,int _buf_size,int *_li) OP_ARG_NONNULL(1);
+
+/**Reads more samples from the stream.
+   \note Although \a _buf_size must indicate the total number of values that
+    can be stored in \a _pcm, the return value is the number of samples
+    <em>per channel</em>.
+   <ol>
+   <li>The channel count cannot be known a priori (reading more samples might
+        advance us into the next link, with a different channel count), so
+        \a _buf_size cannot also be in units of samples per channel,</li>
+   <li>Returning the samples per channel matches the <code>libopus</code> API
+        as closely as we're able,</li>
+   <li>Returning the total number of values instead of samples per channel
+        would mean the caller would need a division to compute the samples per
+        channel, and might worry about the possibility of getting back samples
+        for some channels and not others, and</li>
+   <li>This approach is relatively fool-proof: if an application passes too
+        small a value to \a _buf_size, they will simply get fewer samples back,
+        and if they assume the return value is the total number of values, then
+        they will simply read too few (rather than reading too many and going
+        off the end of the buffer).</li>
+   </ol>
+   \param      _of       The \c OggOpusFile from which to read.
+   \param[out] _pcm      A buffer in which to store the output PCM samples as
+                          signed floats at 48&nbsp;kHz with a nominal range of
+                          <code>[-1.0,1.0]</code>.
+                         Multiple channels are interleaved using the
+                          <a href="http://www.xiph.org/vorbis/doc/Vorbis_I_spec.html#x1-800004.3.9">Vorbis
+                          channel ordering</a>.
+                         This must have room for at least \a _buf_size floats.
+   \param      _buf_size The number of floats that can be stored in \a _pcm.
+                         It is recommended that this be large enough for at
+                          least 120 ms of data at 48 kHz per channel (5760
+                          samples per channel).
+                         Smaller buffers will simply return less data, possibly
+                          consuming more memory to buffer the data internally.
+                         If less than \a _buf_size values are returned,
+                          <tt>libopusfile</tt> makes no guarantee that the
+                          remaining data in \a _pcm will be unmodified.
+   \param[out] _li       The index of the link this data was decoded from.
+                         You may pass <code>NULL</code> if you do not need this
+                          information.
+                         If this function fails (returning a negative value),
+                          this parameter is left unset.
+   \return The number of samples read per channel on success, or a negative
+            value on failure.
+           The channel count can be retrieved on success by calling
+            <code>op_head(_of,*_li)</code>.
+           The number of samples returned may be 0 if the buffer was too small
+            to store even a single sample for all channels, or if end-of-file
+            was reached.
+           The list of possible failure codes follows.
+           Most of them can only be returned by unseekable, chained streams
+            that encounter a new link.
+   \retval #OP_HOLE          There was a hole in the data, and some samples
+                              may have been skipped.
+                             Call this function again to continue decoding
+                              past the hole.
+   \retval #OP_EREAD         An underlying read operation failed.
+                             This may signal a truncation attack from an
+                              <https:> source.
+   \retval #OP_EFAULT        An internal memory allocation failed.
+   \retval #OP_EIMPL         An unseekable stream encountered a new link that
+                              used a feature that is not implemented, such as
+                              an unsupported channel family.
+   \retval #OP_EINVAL        The stream was only partially open.
+   \retval #OP_ENOTFORMAT    An unseekable stream encountered a new link that
+                              did not have any logical Opus streams in it.
+   \retval #OP_EBADHEADER    An unseekable stream encountered a new link with a
+                              required header packet that was not properly
+                              formatted, contained illegal values, or was
+                              missing altogether.
+   \retval #OP_EVERSION      An unseekable stream encountered a new link with
+                              an ID header that contained an unrecognized
+                              version number.
+   \retval #OP_EBADPACKET    Failed to properly decode the next packet.
+   \retval #OP_EBADLINK      We failed to find data we had seen before.
+   \retval #OP_EBADTIMESTAMP An unseekable stream encountered a new link with
+                              a starting timestamp that failed basic validity
+                              checks.*/
+OP_WARN_UNUSED_RESULT int op_read_float(OggOpusFile *_of,
+ float *_pcm,int _buf_size,int *_li) OP_ARG_NONNULL(1);
+
+/**Reads more samples from the stream and downmixes to stereo, if necessary.
+   This function is intended for simple players that want a uniform output
+    format, even if the channel count changes between links in a chained
+    stream.
+   \note \a _buf_size indicates the total number of values that can be stored
+    in \a _pcm, while the return value is the number of samples <em>per
+    channel</em>, even though the channel count is known, for consistency with
+    op_read().
+   \param      _of       The \c OggOpusFile from which to read.
+   \param[out] _pcm      A buffer in which to store the output PCM samples, as
+                          signed native-endian 16-bit values at 48&nbsp;kHz
+                          with a nominal range of <code>[-32768,32767)</code>.
+                         The left and right channels are interleaved in the
+                          buffer.
+                         This must have room for at least \a _buf_size values.
+   \param      _buf_size The number of values that can be stored in \a _pcm.
+                         It is recommended that this be large enough for at
+                          least 120 ms of data at 48 kHz per channel (11520
+                          values total).
+                         Smaller buffers will simply return less data, possibly
+                          consuming more memory to buffer the data internally.
+                         If less than \a _buf_size values are returned,
+                          <tt>libopusfile</tt> makes no guarantee that the
+                          remaining data in \a _pcm will be unmodified.
+   \return The number of samples read per channel on success, or a negative
+            value on failure.
+           The number of samples returned may be 0 if the buffer was too small
+            to store even a single sample for both channels, or if end-of-file
+            was reached.
+           The list of possible failure codes follows.
+           Most of them can only be returned by unseekable, chained streams
+            that encounter a new link.
+   \retval #OP_HOLE          There was a hole in the data, and some samples
+                              may have been skipped.
+                             Call this function again to continue decoding
+                              past the hole.
+   \retval #OP_EREAD         An underlying read operation failed.
+                             This may signal a truncation attack from an
+                              <https:> source.
+   \retval #OP_EFAULT        An internal memory allocation failed.
+   \retval #OP_EIMPL         An unseekable stream encountered a new link that
+                              used a feature that is not implemented, such as
+                              an unsupported channel family.
+   \retval #OP_EINVAL        The stream was only partially open.
+   \retval #OP_ENOTFORMAT    An unseekable stream encountered a new link that
+                              did not have any logical Opus streams in it.
+   \retval #OP_EBADHEADER    An unseekable stream encountered a new link with a
+                              required header packet that was not properly
+                              formatted, contained illegal values, or was
+                              missing altogether.
+   \retval #OP_EVERSION      An unseekable stream encountered a new link with
+                              an ID header that contained an unrecognized
+                              version number.
+   \retval #OP_EBADPACKET    Failed to properly decode the next packet.
+   \retval #OP_EBADLINK      We failed to find data we had seen before.
+   \retval #OP_EBADTIMESTAMP An unseekable stream encountered a new link with
+                              a starting timestamp that failed basic validity
+                              checks.*/
+OP_WARN_UNUSED_RESULT int op_read_stereo(OggOpusFile *_of,
+ opus_int16 *_pcm,int _buf_size) OP_ARG_NONNULL(1);
+
+/**Reads more samples from the stream and downmixes to stereo, if necessary.
+   This function is intended for simple players that want a uniform output
+    format, even if the channel count changes between links in a chained
+    stream.
+   \note \a _buf_size indicates the total number of values that can be stored
+    in \a _pcm, while the return value is the number of samples <em>per
+    channel</em>, even though the channel count is known, for consistency with
+    op_read_float().
+   \param      _of       The \c OggOpusFile from which to read.
+   \param[out] _pcm      A buffer in which to store the output PCM samples, as
+                          signed floats at 48&nbsp;kHz with a nominal range of
+                          <code>[-1.0,1.0]</code>.
+                         The left and right channels are interleaved in the
+                          buffer.
+                         This must have room for at least \a _buf_size values.
+   \param      _buf_size The number of values that can be stored in \a _pcm.
+                         It is recommended that this be large enough for at
+                          least 120 ms of data at 48 kHz per channel (11520
+                          values total).
+                         Smaller buffers will simply return less data, possibly
+                          consuming more memory to buffer the data internally.
+                         If less than \a _buf_size values are returned,
+                          <tt>libopusfile</tt> makes no guarantee that the
+                          remaining data in \a _pcm will be unmodified.
+   \return The number of samples read per channel on success, or a negative
+            value on failure.
+           The number of samples returned may be 0 if the buffer was too small
+            to store even a single sample for both channels, or if end-of-file
+            was reached.
+           The list of possible failure codes follows.
+           Most of them can only be returned by unseekable, chained streams
+            that encounter a new link.
+   \retval #OP_HOLE          There was a hole in the data, and some samples
+                              may have been skipped.
+                             Call this function again to continue decoding
+                              past the hole.
+   \retval #OP_EREAD         An underlying read operation failed.
+                             This may signal a truncation attack from an
+                              <https:> source.
+   \retval #OP_EFAULT        An internal memory allocation failed.
+   \retval #OP_EIMPL         An unseekable stream encountered a new link that
+                              used a feature that is not implemented, such as
+                              an unsupported channel family.
+   \retval #OP_EINVAL        The stream was only partially open.
+   \retval #OP_ENOTFORMAT    An unseekable stream encountered a new link that
+                              that did not have any logical Opus streams in it.
+   \retval #OP_EBADHEADER    An unseekable stream encountered a new link with a
+                              required header packet that was not properly
+                              formatted, contained illegal values, or was
+                              missing altogether.
+   \retval #OP_EVERSION      An unseekable stream encountered a new link with
+                              an ID header that contained an unrecognized
+                              version number.
+   \retval #OP_EBADPACKET    Failed to properly decode the next packet.
+   \retval #OP_EBADLINK      We failed to find data we had seen before.
+   \retval #OP_EBADTIMESTAMP An unseekable stream encountered a new link with
+                              a starting timestamp that failed basic validity
+                              checks.*/
+OP_WARN_UNUSED_RESULT int op_read_float_stereo(OggOpusFile *_of,
+ float *_pcm,int _buf_size) OP_ARG_NONNULL(1);
+
+/*@}*/
+/*@}*/
+
+# if OP_GNUC_PREREQ(4,0)
+#  pragma GCC visibility pop
+# endif
+
+# if defined(__cplusplus)
+}
+# endif
+
+#endif
diff --git a/opusfile/stream.c b/opusfile/stream.c
new file mode 100644
index 0000000..6a85197
--- /dev/null
+++ b/opusfile/stream.c
@@ -0,0 +1,364 @@
+/********************************************************************
+ *                                                                  *
+ * THIS FILE IS PART OF THE libopusfile SOFTWARE CODEC SOURCE CODE. *
+ * USE, DISTRIBUTION AND REPRODUCTION OF THIS LIBRARY SOURCE IS     *
+ * GOVERNED BY A BSD-STYLE SOURCE LICENSE INCLUDED WITH THIS SOURCE *
+ * IN 'COPYING'. PLEASE READ THESE TERMS BEFORE DISTRIBUTING.       *
+ *                                                                  *
+ * THE libopusfile SOURCE CODE IS (C) COPYRIGHT 1994-2012           *
+ * by the Xiph.Org Foundation and contributors http://www.xiph.org/ *
+ *                                                                  *
+ ********************************************************************
+
+ function: stdio-based convenience library for opening/seeking/decoding
+ last mod: $Id: vorbisfile.c 17573 2010-10-27 14:53:59Z xiphmont $
+
+ ********************************************************************/
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include "internal.h"
+#include <sys/types.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <string.h>
+#if defined(_WIN32)
+# include <io.h>
+#endif
+
+typedef struct OpusMemStream OpusMemStream;
+
+#define OP_MEM_SIZE_MAX (~(size_t)0>>1)
+#define OP_MEM_DIFF_MAX ((ptrdiff_t)OP_MEM_SIZE_MAX)
+
+/*The context information needed to read from a block of memory as if it were a
+   file.*/
+struct OpusMemStream{
+  /*The block of memory to read from.*/
+  const unsigned char *data;
+  /*The total size of the block.
+    This must be at most OP_MEM_SIZE_MAX to prevent signed overflow while
+     seeking.*/
+  ptrdiff_t            size;
+  /*The current file position.
+    This is allowed to be set arbitrarily greater than size (i.e., past the end
+     of the block, though we will not read data past the end of the block), but
+     is not allowed to be negative (i.e., before the beginning of the block).*/
+  ptrdiff_t            pos;
+};
+
+static int op_fread(void *_stream,unsigned char *_ptr,int _buf_size){
+  FILE   *stream;
+  size_t  ret;
+  /*Check for empty read.*/
+  if(_buf_size<=0)return 0;
+  stream=(FILE *)_stream;
+  ret=fread(_ptr,1,_buf_size,stream);
+  OP_ASSERT(ret<=(size_t)_buf_size);
+  /*If ret==0 and !feof(stream), there was a read error.*/
+  return ret>0||feof(stream)?(int)ret:OP_EREAD;
+}
+
+static int op_fseek(void *_stream,opus_int64 _offset,int _whence){
+#if defined(_WIN32)
+  /*_fseeki64() is not exposed until MSCVCRT80.
+    This is the default starting with MSVC 2005 (_MSC_VER>=1400), but we want
+     to allow linking against older MSVCRT versions for compatibility back to
+     XP without installing extra runtime libraries.
+    i686-pc-mingw32 does not have fseeko() and requires
+     __MSVCRT_VERSION__>=0x800 for _fseeki64(), which screws up linking with
+     other libraries (that don't use MSVCRT80 from MSVC 2005 by default).
+    i686-w64-mingw32 does have fseeko() and respects _FILE_OFFSET_BITS, but I
+     don't know how to detect that at compile time.
+    We could just use fseeko64() (which is available in both), but its
+     implemented using fgetpos()/fsetpos() just like this code, except without
+     the overflow checking, so we prefer our version.*/
+  opus_int64 pos;
+  /*We don't use fpos_t directly because it might be a struct if __STDC__ is
+     non-zero or _INTEGRAL_MAX_BITS < 64.
+    I'm not certain when the latter is true, but someone could in theory set
+     the former.
+    Either way, it should be binary compatible with a normal 64-bit int (this
+     assumption is not portable, but I believe it is true for MSVCRT).*/
+  OP_ASSERT(sizeof(pos)==sizeof(fpos_t));
+  /*Translate the seek to an absolute one.*/
+  if(_whence==SEEK_CUR){
+    int ret;
+    ret=fgetpos((FILE *)_stream,(fpos_t *)&pos);
+    if(ret)return ret;
+  }
+  else if(_whence==SEEK_END)pos=_filelengthi64(_fileno((FILE *)_stream));
+  else if(_whence==SEEK_SET)pos=0;
+  else return -1;
+  /*Check for errors or overflow.*/
+  if(pos<0||_offset<-pos||_offset>OP_INT64_MAX-pos)return -1;
+  pos+=_offset;
+  return fsetpos((FILE *)_stream,(fpos_t *)&pos);
+#else
+  /*This function actually conforms to the SUSv2 and POSIX.1-2001, so we prefer
+     it except on Windows.*/
+  return fseeko((FILE *)_stream,(off_t)_offset,_whence);
+#endif
+}
+
+static opus_int64 op_ftell(void *_stream){
+#if defined(_WIN32)
+  /*_ftelli64() is not exposed until MSCVCRT80, and ftello()/ftello64() have
+     the same problems as fseeko()/fseeko64() in MingW.
+    See above for a more detailed explanation.*/
+  opus_int64 pos;
+  OP_ASSERT(sizeof(pos)==sizeof(fpos_t));
+  return fgetpos((FILE *)_stream,(fpos_t *)&pos)?-1:pos;
+#else
+  /*This function actually conforms to the SUSv2 and POSIX.1-2001, so we prefer
+     it except on Windows.*/
+  return ftello((FILE *)_stream);
+#endif
+}
+
+static const OpusFileCallbacks OP_FILE_CALLBACKS={
+  op_fread,
+  op_fseek,
+  op_ftell,
+  (op_close_func)fclose
+};
+
+#if defined(_WIN32)
+# include <stddef.h>
+# include <errno.h>
+
+/*Windows doesn't accept UTF-8 by default, and we don't have a wchar_t API,
+   so if we just pass the path to fopen(), then there'd be no way for a user
+   of our API to open a Unicode filename.
+  Instead, we translate from UTF-8 to UTF-16 and use Windows' wchar_t API.
+  This makes this API more consistent with platforms where the character set
+   used by fopen is the same as used on disk, which is generally UTF-8, and
+   with our metadata API, which always uses UTF-8.*/
+static wchar_t *op_utf8_to_utf16(const char *_src){
+  wchar_t *dst;
+  size_t   len;
+  len=strlen(_src);
+  /*Worst-case output is 1 wide character per 1 input character.*/
+  dst=(wchar_t *)_ogg_malloc(sizeof(*dst)*(len+1));
+  if(dst!=NULL){
+    size_t si;
+    size_t di;
+    for(di=si=0;si<len;si++){
+      int c0;
+      c0=(unsigned char)_src[si];
+      if(!(c0&0x80)){
+        /*Start byte says this is a 1-byte sequence.*/
+        dst[di++]=(wchar_t)c0;
+        continue;
+      }
+      else{
+        int c1;
+        /*This is safe, because c0 was not 0 and _src is NUL-terminated.*/
+        c1=(unsigned char)_src[si+1];
+        if((c1&0xC0)==0x80){
+          /*Found at least one continuation byte.*/
+          if((c0&0xE0)==0xC0){
+            wchar_t w;
+            /*Start byte says this is a 2-byte sequence.*/
+            w=(c0&0x1F)<<6|c1&0x3F;
+            if(w>=0x80U){
+              /*This is a 2-byte sequence that is not overlong.*/
+              dst[di++]=w;
+              si++;
+              continue;
+            }
+          }
+          else{
+            int c2;
+            /*This is safe, because c1 was not 0 and _src is NUL-terminated.*/
+            c2=(unsigned char)_src[si+2];
+            if((c2&0xC0)==0x80){
+              /*Found at least two continuation bytes.*/
+              if((c0&0xF0)==0xE0){
+                wchar_t w;
+                /*Start byte says this is a 3-byte sequence.*/
+                w=(c0&0xF)<<12|(c1&0x3F)<<6|c2&0x3F;
+                if(w>=0x800U&&(w<0xD800||w>=0xE000)&&w<0xFFFE){
+                  /*This is a 3-byte sequence that is not overlong, not a
+                     UTF-16 surrogate pair value, and not a 'not a character'
+                     value.*/
+                  dst[di++]=w;
+                  si+=2;
+                  continue;
+                }
+              }
+              else{
+                int c3;
+                /*This is safe, because c2 was not 0 and _src is
+                   NUL-terminated.*/
+                c3=(unsigned char)_src[si+3];
+                if((c3&0xC0)==0x80){
+                  /*Found at least three continuation bytes.*/
+                  if((c0&0xF8)==0xF0){
+                    opus_uint32 w;
+                    /*Start byte says this is a 4-byte sequence.*/
+                    w=(c0&7)<<18|(c1&0x3F)<<12|(c2&0x3F)<<6&(c3&0x3F);
+                    if(w>=0x10000U&&w<0x110000U){
+                      /*This is a 4-byte sequence that is not overlong and not
+                         greater than the largest valid Unicode code point.
+                        Convert it to a surrogate pair.*/
+                      w-=0x10000;
+                      dst[di++]=(wchar_t)(0xD800+(w>>10));
+                      dst[di++]=(wchar_t)(0xDC00+(w&0x3FF));
+                      si+=3;
+                      continue;
+                    }
+                  }
+                }
+              }
+            }
+          }
+        }
+      }
+      /*If we got here, we encountered an illegal UTF-8 sequence.*/
+      _ogg_free(dst);
+      return NULL;
+    }
+    OP_ASSERT(di<=len);
+    dst[di]='\0';
+  }
+  return dst;
+}
+
+#endif
+
+void *op_fopen(OpusFileCallbacks *_cb,const char *_path,const char *_mode){
+  FILE *fp;
+#if !defined(_WIN32)
+  fp=fopen(_path,_mode);
+#else
+  fp=NULL;
+  {
+    wchar_t *wpath;
+    wchar_t *wmode;
+    wpath=op_utf8_to_utf16(_path);
+    wmode=op_utf8_to_utf16(_mode);
+    if(wmode==NULL)errno=EINVAL;
+    else if(wpath==NULL)errno=ENOENT;
+    else fp=_wfopen(wpath,wmode);
+    _ogg_free(wmode);
+    _ogg_free(wpath);
+  }
+#endif
+  if(fp!=NULL)*_cb=*&OP_FILE_CALLBACKS;
+  return fp;
+}
+
+void *op_fdopen(OpusFileCallbacks *_cb,int _fd,const char *_mode){
+  FILE *fp;
+  fp=fdopen(_fd,_mode);
+  if(fp!=NULL)*_cb=*&OP_FILE_CALLBACKS;
+  return fp;
+}
+
+void *op_freopen(OpusFileCallbacks *_cb,const char *_path,const char *_mode,
+ void *_stream){
+  FILE *fp;
+#if !defined(_WIN32)
+  fp=freopen(_path,_mode,(FILE *)_stream);
+#else
+  fp=NULL;
+  {
+    wchar_t *wpath;
+    wchar_t *wmode;
+    wpath=op_utf8_to_utf16(_path);
+    wmode=op_utf8_to_utf16(_mode);
+    if(wmode==NULL)errno=EINVAL;
+    else if(wpath==NULL)errno=ENOENT;
+    else fp=_wfreopen(wpath,wmode,(FILE *)_stream);
+    _ogg_free(wmode);
+    _ogg_free(wpath);
+  }
+#endif
+  if(fp!=NULL)*_cb=*&OP_FILE_CALLBACKS;
+  return fp;
+}
+
+static int op_mem_read(void *_stream,unsigned char *_ptr,int _buf_size){
+  OpusMemStream *stream;
+  ptrdiff_t      size;
+  ptrdiff_t      pos;
+  stream=(OpusMemStream *)_stream;
+  /*Check for empty read.*/
+  if(_buf_size<=0)return 0;
+  size=stream->size;
+  pos=stream->pos;
+  /*Check for EOF.*/
+  if(pos>=size)return 0;
+  /*Check for a short read.*/
+  _buf_size=(int)OP_MIN(size-pos,_buf_size);
+  memcpy(_ptr,stream->data+pos,_buf_size);
+  pos+=_buf_size;
+  stream->pos=pos;
+  return _buf_size;
+}
+
+static int op_mem_seek(void *_stream,opus_int64 _offset,int _whence){
+  OpusMemStream *stream;
+  ptrdiff_t      pos;
+  stream=(OpusMemStream *)_stream;
+  pos=stream->pos;
+  OP_ASSERT(pos>=0);
+  switch(_whence){
+    case SEEK_SET:{
+      /*Check for overflow:*/
+      if(_offset<0||_offset>OP_MEM_DIFF_MAX)return -1;
+      pos=(ptrdiff_t)_offset;
+    }break;
+    case SEEK_CUR:{
+      /*Check for overflow:*/
+      if(_offset<-pos||_offset>OP_MEM_DIFF_MAX-pos)return -1;
+      pos=(ptrdiff_t)(pos+_offset);
+    }break;
+    case SEEK_END:{
+      ptrdiff_t size;
+      size=stream->size;
+      OP_ASSERT(size>=0);
+      /*Check for overflow:*/
+      if(_offset>size||_offset<size-OP_MEM_DIFF_MAX)return -1;
+      pos=(ptrdiff_t)(size-_offset);
+    }break;
+    default:return -1;
+  }
+  stream->pos=pos;
+  return 0;
+}
+
+static opus_int64 op_mem_tell(void *_stream){
+  OpusMemStream *stream;
+  stream=(OpusMemStream *)_stream;
+  return (ogg_int64_t)stream->pos;
+}
+
+static int op_mem_close(void *_stream){
+  _ogg_free(_stream);
+  return 0;
+}
+
+static const OpusFileCallbacks OP_MEM_CALLBACKS={
+  op_mem_read,
+  op_mem_seek,
+  op_mem_tell,
+  op_mem_close
+};
+
+void *op_mem_stream_create(OpusFileCallbacks *_cb,
+ const unsigned char *_data,size_t _size){
+  OpusMemStream *stream;
+  if(_size>OP_MEM_SIZE_MAX)return NULL;
+  stream=(OpusMemStream *)_ogg_malloc(sizeof(*stream));
+  if(stream!=NULL){
+    *_cb=*&OP_MEM_CALLBACKS;
+    stream->data=_data;
+    stream->size=_size;
+    stream->pos=0;
+  }
+  return stream;
+}