vorbisfile.c 44 KB
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/********************************************************************
 *                                                                  *
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 * THIS FILE IS PART OF THE OggVorbis SOFTWARE CODEC SOURCE CODE.   *
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 * 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.       *
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 *                                                                  *
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 * THE OggVorbis SOURCE CODE IS (C) COPYRIGHT 1994-2002             *
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 * by the XIPHOPHORUS Company http://www.xiph.org/                  *
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 *                                                                  *
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 ********************************************************************

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 function: stdio-based convenience library for opening/seeking/decoding
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 last mod: $Id: vorbisfile.c,v 1.56 2002/02/28 04:12:48 xiphmont Exp $
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 ********************************************************************/

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#include <stdlib.h>
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#include <stdio.h>
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#include <errno.h>
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#include <string.h>
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#include <math.h>
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#include "vorbis/codec.h"
#include "vorbis/vorbisfile.h"

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#include "os.h"
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#include "misc.h"
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/* A 'chained bitstream' is a Vorbis bitstream that contains more than
   one logical bitstream arranged end to end (the only form of Ogg
   multiplexing allowed in a Vorbis bitstream; grouping [parallel
   multiplexing] is not allowed in Vorbis) */

/* A Vorbis file can be played beginning to end (streamed) without
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   worrying ahead of time about chaining (see decoder_example.c).  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. */
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/* We can handle things a number of ways; we can determine the entire
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   bitstream structure right off the bat, or find pieces on demand.
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   This example determines and caches structure for the entire
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   bitstream, but builds a virtual decoder on the fly when moving
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   between links in the chain. */
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/* 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
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   picking some portion of the stream roughly in the desired area if
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   we only want coarse navigation through the stream. */
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/*************************************************************************
 * Many, many internal helpers.  The intention is not to be confusing; 
 * rampant duplication and monolithic function implementation would be 
 * harder to understand anyway.  The high level functions are last.  Begin
 * grokking near the end of the file */

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/* read a little more data from the file/pipe into the ogg_sync framer
*/
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#define CHUNKSIZE 8500 /* a shade over 8k; anyone using pages well
                          over 8k gets what they deserve */
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static long _get_data(OggVorbis_File *vf){
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  errno=0;
  if(vf->datasource){
    char *buffer=ogg_sync_buffer(&vf->oy,CHUNKSIZE);
    long bytes=(vf->callbacks.read_func)(buffer,1,CHUNKSIZE,vf->datasource);
    if(bytes>0)ogg_sync_wrote(&vf->oy,bytes);
    if(bytes==0 && errno)return(-1);
    return(bytes);
  }else
    return(0);
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}

/* save a tiny smidge of verbosity to make the code more readable */
static void _seek_helper(OggVorbis_File *vf,long offset){
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  if(vf->datasource){ 
    (vf->callbacks.seek_func)(vf->datasource, offset, SEEK_SET);
    vf->offset=offset;
    ogg_sync_reset(&vf->oy);
  }else{
    /* shouldn't happen unless someone writes a broken callback */
    return;
  }
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}

/* The read/seek functions track absolute position within the stream */

/* 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 cached only
	      n) search for a new page beginning for n bytes

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   return:   <0) did not find a page (OV_FALSE, OV_EOF, OV_EREAD)
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              n) found a page at absolute offset n */

static long _get_next_page(OggVorbis_File *vf,ogg_page *og,int boundary){
  if(boundary>0)boundary+=vf->offset;
  while(1){
    long more;

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    if(boundary>0 && vf->offset>=boundary)return(OV_FALSE);
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    more=ogg_sync_pageseek(&vf->oy,og);
    
    if(more<0){
      /* skipped n bytes */
      vf->offset-=more;
    }else{
      if(more==0){
	/* send more paramedics */
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	if(!boundary)return(OV_FALSE);
	{
	  long ret=_get_data(vf);
	  if(ret==0)return(OV_EOF);
	  if(ret<0)return(OV_EREAD);
	}
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      }else{
	/* got a page.  Return the offset at the page beginning,
           advance the internal offset past the page end */
	long ret=vf->offset;
	vf->offset+=more;
	return(ret);
	
      }
    }
  }
}

/* find the latest page beginning before the current stream cursor
   position. Much dirtier than the above as Ogg doesn't have any
   backward search linkage.  no 'readp' as it will certainly have to
   read. */
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/* returns offset or OV_EREAD, OV_FAULT */
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static long _get_prev_page(OggVorbis_File *vf,ogg_page *og){
  long begin=vf->offset;
  long ret;
  int offset=-1;

  while(offset==-1){
    begin-=CHUNKSIZE;
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    if(begin<0)
      begin=0;
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    _seek_helper(vf,begin);
    while(vf->offset<begin+CHUNKSIZE){
      ret=_get_next_page(vf,og,begin+CHUNKSIZE-vf->offset);
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      if(ret==OV_EREAD)return(OV_EREAD);
      if(ret<0){
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	break;
      }else{
	offset=ret;
      }
    }
  }

  /* we have the offset.  Actually snork and hold the page now */
  _seek_helper(vf,offset);
  ret=_get_next_page(vf,og,CHUNKSIZE);
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  if(ret<0)
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    /* this shouldn't be possible */
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    return(OV_EFAULT);

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  return(offset);
}

/* finds each bitstream link one at a time using a bisection search
   (has to begin by knowing the offset of the lb's initial page).
   Recurses for each link so it can alloc the link storage after
   finding them all, then unroll and fill the cache at the same time */
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static int _bisect_forward_serialno(OggVorbis_File *vf,
				    long begin,
				    long searched,
				    long end,
				    long currentno,
				    long m){
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  long endsearched=end;
  long next=end;
  ogg_page og;
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  long ret;
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  /* the below guards against garbage seperating the last and
     first pages of two links. */
  while(searched<endsearched){
    long bisect;
    
    if(endsearched-searched<CHUNKSIZE){
      bisect=searched;
    }else{
      bisect=(searched+endsearched)/2;
    }
    
    _seek_helper(vf,bisect);
    ret=_get_next_page(vf,&og,-1);
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    if(ret==OV_EREAD)return(OV_EREAD);
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    if(ret<0 || ogg_page_serialno(&og)!=currentno){
      endsearched=bisect;
      if(ret>=0)next=ret;
    }else{
      searched=ret+og.header_len+og.body_len;
    }
  }
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  _seek_helper(vf,next);
  ret=_get_next_page(vf,&og,-1);
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  if(ret==OV_EREAD)return(OV_EREAD);
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  if(searched>=end || ret<0){
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    vf->links=m+1;
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    vf->offsets=_ogg_malloc((m+2)*sizeof(*vf->offsets));
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    vf->offsets[m+1]=searched;
  }else{
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    ret=_bisect_forward_serialno(vf,next,vf->offset,
				 end,ogg_page_serialno(&og),m+1);
    if(ret==OV_EREAD)return(OV_EREAD);
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  }
  
  vf->offsets[m]=begin;
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  return(0);
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}
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/* uses the local ogg_stream storage in vf; this is important for
   non-streaming input sources */
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static int _fetch_headers(OggVorbis_File *vf,vorbis_info *vi,vorbis_comment *vc,
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			  long *serialno,ogg_page *og_ptr){
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  ogg_page og;
  ogg_packet op;
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  int i,ret=0;
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  if(!og_ptr){
    ret=_get_next_page(vf,&og,CHUNKSIZE);
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    if(ret==OV_EREAD)return(OV_EREAD);
    if(ret<0)return OV_ENOTVORBIS;
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    og_ptr=&og;
  }

  if(serialno)*serialno=ogg_page_serialno(og_ptr);
  ogg_stream_init(&vf->os,ogg_page_serialno(og_ptr));
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  vf->ready_state=STREAMSET;
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  /* extract the initial header from the first page and verify that the
     Ogg bitstream is in fact Vorbis data */
  
  vorbis_info_init(vi);
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  vorbis_comment_init(vc);
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  i=0;
  while(i<3){
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    ogg_stream_pagein(&vf->os,og_ptr);
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    while(i<3){
      int result=ogg_stream_packetout(&vf->os,&op);
      if(result==0)break;
      if(result==-1){
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	ret=OV_EBADHEADER;
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	goto bail_header;
      }
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      if((ret=vorbis_synthesis_headerin(vi,vc,&op))){
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	goto bail_header;
      }
      i++;
    }
    if(i<3)
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      if(_get_next_page(vf,og_ptr,CHUNKSIZE)<0){
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	ret=OV_EBADHEADER;
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	goto bail_header;
      }
  }
  return 0; 
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 bail_header:
  vorbis_info_clear(vi);
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  vorbis_comment_clear(vc);
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  ogg_stream_clear(&vf->os);
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  vf->ready_state=OPENED;

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  return ret;
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}
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/* last step of the OggVorbis_File initialization; get all the
   vorbis_info structs and PCM positions.  Only called by the seekable
   initialization (local stream storage is hacked slightly; pay
   attention to how that's done) */
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/* this is void and does not propogate errors up because we want to be
   able to open and use damaged bitstreams as well as we can.  Just
   watch out for missing information for links in the OggVorbis_File
   struct */
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static void _prefetch_all_headers(OggVorbis_File *vf, long dataoffset){
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  ogg_page og;
  int i,ret;
  
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  vf->vi=_ogg_realloc(vf->vi,vf->links*sizeof(*vf->vi));
  vf->vc=_ogg_realloc(vf->vc,vf->links*sizeof(*vf->vc));
  vf->dataoffsets=_ogg_malloc(vf->links*sizeof(*vf->dataoffsets));
  vf->pcmlengths=_ogg_malloc(vf->links*sizeof(*vf->pcmlengths));
  vf->serialnos=_ogg_malloc(vf->links*sizeof(*vf->serialnos));
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  for(i=0;i<vf->links;i++){
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    if(i==0){
      /* we already grabbed the initial header earlier.  Just set the offset */
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      vf->dataoffsets[i]=dataoffset;
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    }else{
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      /* seek to the location of the initial header */
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      _seek_helper(vf,vf->offsets[i]);
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      if(_fetch_headers(vf,vf->vi+i,vf->vc+i,NULL,NULL)<0){
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    	vf->dataoffsets[i]=-1;
      }else{
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	vf->dataoffsets[i]=vf->offset;
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        ogg_stream_clear(&vf->os);
      }
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    }
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    /* get the serial number and PCM length of this link. To do this,
       get the last page of the stream */
    {
      long end=vf->offsets[i+1];
      _seek_helper(vf,end);
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      while(1){
	ret=_get_prev_page(vf,&og);
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	if(ret<0){
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	  /* this should not be possible */
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	  vorbis_info_clear(vf->vi+i);
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	  vorbis_comment_clear(vf->vc+i);
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	  break;
	}
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	if(ogg_page_granulepos(&og)!=-1){
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	  vf->serialnos[i]=ogg_page_serialno(&og);
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	  vf->pcmlengths[i]=ogg_page_granulepos(&og);
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	  break;
	}
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	vf->offset=ret;
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      }
    }
  }
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}

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static void _make_decode_ready(OggVorbis_File *vf){
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  if(vf->ready_state!=STREAMSET)return;
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  if(vf->seekable){
    vorbis_synthesis_init(&vf->vd,vf->vi+vf->current_link);
  }else{
    vorbis_synthesis_init(&vf->vd,vf->vi);
  }    
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  vorbis_block_init(&vf->vd,&vf->vb);
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  vf->ready_state=INITSET;
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  return;
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}

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static int _open_seekable2(OggVorbis_File *vf){
  long serialno=vf->current_serialno,end;
  long dataoffset=vf->offset;
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  ogg_page og;
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  /* we're partially open and have a first link header state in
     storage in vf */
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  /* we can seek, so set out learning all about this file */
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  (vf->callbacks.seek_func)(vf->datasource,0,SEEK_END);
  vf->offset=vf->end=(vf->callbacks.tell_func)(vf->datasource);
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  /* We get the offset for the last page of the physical bitstream.
     Most OggVorbis files will contain a single logical bitstream */
  end=_get_prev_page(vf,&og);
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  if(end<0){
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    ov_clear(vf);
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    return(end);
  }
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  /* more than one logical bitstream? */
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  if(ogg_page_serialno(&og)!=serialno){
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    /* Chained bitstream. Bisect-search each logical bitstream
       section.  Do so based on serial number only */
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    if(_bisect_forward_serialno(vf,0,0,end+1,serialno,0)<0){
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      ov_clear(vf);
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      return(OV_EREAD);
    }
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  }else{

    /* Only one logical bitstream */
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    if(_bisect_forward_serialno(vf,0,end,end+1,serialno,0)){
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      ov_clear(vf);
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      return(OV_EREAD);
    }
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  }

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  /* the initial header memory is referenced by vf after; don't free it */
  _prefetch_all_headers(vf,dataoffset);
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  return(ov_raw_seek(vf,0));
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}
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/* clear out the current logical bitstream decoder */ 
static void _decode_clear(OggVorbis_File *vf){
  ogg_stream_clear(&vf->os);
  vorbis_dsp_clear(&vf->vd);
  vorbis_block_clear(&vf->vb);
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  vf->ready_state=OPENED;
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  vf->bittrack=0.f;
  vf->samptrack=0.f;
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}

/* fetch and process a packet.  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 pcm_offset up to
   date (seek and read both use this.  seek uses a special hack with
   readp). 

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   return: <0) error, OV_HOLE (lost packet) or OV_EOF
            0) need more data (only if readp==0)
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	    1) got a packet 
*/

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static int _fetch_and_process_packet(OggVorbis_File *vf,
				     ogg_packet *op_in,
				     int readp){
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  ogg_page og;

  /* handle one packet.  Try to fetch it from current stream state */
  /* extract packets from page */
  while(1){
    
    /* process a packet if we can.  If the machine isn't loaded,
       neither is a page */
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    if(vf->ready_state==INITSET){
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      while(1) {
      	ogg_packet op;
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      	ogg_packet *op_ptr=(op_in?op_in:&op);
	int result=ogg_stream_packetout(&vf->os,op_ptr);
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	ogg_int64_t granulepos;

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	op_in=NULL;
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	if(result==-1)return(OV_HOLE); /* hole in the data. */
	if(result>0){
	  /* got a packet.  process it */
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	  granulepos=op_ptr->granulepos;
	  if(!vorbis_synthesis(&vf->vb,op_ptr)){ /* lazy check for lazy
						    header handling.  The
						    header packets aren't
						    audio, so if/when we
						    submit them,
						    vorbis_synthesis will
						    reject them */
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	    /* suck in the synthesis data and track bitrate */
	    {
	      int oldsamples=vorbis_synthesis_pcmout(&vf->vd,NULL);
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	      /* for proper use of libvorbis within libvorbisfile,
                 oldsamples will always be zero. */
	      if(oldsamples)return(OV_EFAULT);
	      
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	      vorbis_synthesis_blockin(&vf->vd,&vf->vb);
	      vf->samptrack+=vorbis_synthesis_pcmout(&vf->vd,NULL)-oldsamples;
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	      vf->bittrack+=op_ptr->bytes*8;
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	    }
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	    /* update the pcm offset. */
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	    if(granulepos!=-1 && !op_ptr->e_o_s){
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	      int link=(vf->seekable?vf->current_link:0);
	      int i,samples;
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	      /* this packet has a pcm_offset on it (the last packet
	         completed on a page carries the offset) After processing
	         (above), we know the pcm position of the *last* sample
	         ready to be returned. Find the offset of the *first*

	         As an aside, this trick is inaccurate if we begin
	         reading anew right at the last page; the end-of-stream
	         granulepos declares the last frame in the stream, and the
	         last packet of the last page may be a partial frame.
	         So, we need a previous granulepos from an in-sequence page
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	         to have a reference point.  Thus the !op_ptr->e_o_s clause
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	         above */
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	      samples=vorbis_synthesis_pcmout(&vf->vd,NULL);
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	      granulepos-=samples;
	      for(i=0;i<link;i++)
	        granulepos+=vf->pcmlengths[i];
	      vf->pcm_offset=granulepos;
	    }
	    return(1);
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	  }
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	}
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	else 
	  break;
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      }
    }

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    if(vf->ready_state>=OPENED){
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      if(!readp)return(0);
      if(_get_next_page(vf,&og,-1)<0)return(OV_EOF); /* eof. 
							leave unitialized */
      /* bitrate tracking; add the header's bytes here, the body bytes
	 are done by packet above */
      vf->bittrack+=og.header_len*8;
      
      /* has our decoding just traversed a bitstream boundary? */
      if(vf->ready_state==INITSET){
	if(vf->current_serialno!=ogg_page_serialno(&og)){
	  _decode_clear(vf);
	  
	  if(!vf->seekable){
	    vorbis_info_clear(vf->vi);
	    vorbis_comment_clear(vf->vc);
	  }
	}
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      }
    }

    /* 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
    */

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    if(vf->ready_state!=INITSET){ 
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      int link;
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      if(vf->ready_state<STREAMSET){
	if(vf->seekable){
	  vf->current_serialno=ogg_page_serialno(&og);
	  
	  /* match the serialno to bitstream section.  We use this rather than
	     offset positions to avoid problems near logical bitstream
	     boundaries */
	  for(link=0;link<vf->links;link++)
	    if(vf->serialnos[link]==vf->current_serialno)break;
	  if(link==vf->links)return(OV_EBADLINK); /* sign of a bogus
						     stream.  error out,
						     leave machine
						     uninitialized */
	  
	  vf->current_link=link;
	  
	  ogg_stream_init(&vf->os,vf->current_serialno);
	  ogg_stream_reset(&vf->os); 
	  vf->ready_state=STREAMSET;
	  
	}else{
	  /* we're streaming */
	  /* fetch the three header packets, build the info struct */
	  
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	  int ret=_fetch_headers(vf,vf->vi,vf->vc,&vf->current_serialno,&og);
	  if(ret)return(ret);
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	  vf->current_link++;
	  link=0;
	}
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      }
      
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      _make_decode_ready(vf);
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    }
    ogg_stream_pagein(&vf->os,&og);
  }
}

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static int _fseek64_wrap(FILE *f,ogg_int64_t off,int whence){
  if(f==NULL)return(-1);
  return fseek(f,(int)off,whence);
}

static int _ov_open1(void *f,OggVorbis_File *vf,char *initial,
		     long ibytes, ov_callbacks callbacks){
  long offset=(f?callbacks.seek_func(f,0,SEEK_CUR):-1);
  int ret;

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  memset(vf,0,sizeof(*vf));
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  vf->datasource=f;
  vf->callbacks = callbacks;

  /* init the framing state */
  ogg_sync_init(&vf->oy);

  /* perhaps some data was previously read into a buffer for testing
     against other stream types.  Allow initialization from this
     previously read data (as we may be reading from a non-seekable
     stream) */
  if(initial){
    char *buffer=ogg_sync_buffer(&vf->oy,ibytes);
    memcpy(buffer,initial,ibytes);
    ogg_sync_wrote(&vf->oy,ibytes);
  }

  /* can we seek? Stevens suggests the seek test was portable */
  if(offset!=-1)vf->seekable=1;

  /* No seeking yet; Set up a 'single' (current) logical bitstream
     entry for partial open */
  vf->links=1;
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  vf->vi=_ogg_calloc(vf->links,sizeof(*vf->vi));
  vf->vc=_ogg_calloc(vf->links,sizeof(*vf->vc));
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  /* Try to fetch the headers, maintaining all the storage */
  if((ret=_fetch_headers(vf,vf->vi,vf->vc,&vf->current_serialno,NULL))<0){
    vf->datasource=NULL;
    ov_clear(vf);
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  }else if(vf->ready_state < PARTOPEN)
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    vf->ready_state=PARTOPEN;
  return(ret);
}

static int _ov_open2(OggVorbis_File *vf){
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  if(vf->ready_state < OPENED)
    vf->ready_state=OPENED;
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  if(vf->seekable){
    int ret=_open_seekable2(vf);
    if(ret){
      vf->datasource=NULL;
      ov_clear(vf);
    }
    return(ret);
  }
  return 0;
}


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/* clear out the OggVorbis_File struct */
int ov_clear(OggVorbis_File *vf){
  if(vf){
    vorbis_block_clear(&vf->vb);
    vorbis_dsp_clear(&vf->vd);
    ogg_stream_clear(&vf->os);
    
    if(vf->vi && vf->links){
      int i;
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      for(i=0;i<vf->links;i++){
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	vorbis_info_clear(vf->vi+i);
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	vorbis_comment_clear(vf->vc+i);
      }
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      _ogg_free(vf->vi);
      _ogg_free(vf->vc);
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    }
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    if(vf->dataoffsets)_ogg_free(vf->dataoffsets);
    if(vf->pcmlengths)_ogg_free(vf->pcmlengths);
    if(vf->serialnos)_ogg_free(vf->serialnos);
    if(vf->offsets)_ogg_free(vf->offsets);
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    ogg_sync_clear(&vf->oy);
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    if(vf->datasource)(vf->callbacks.close_func)(vf->datasource);
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    memset(vf,0,sizeof(*vf));
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  }
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#ifdef DEBUG_LEAKS
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  _VDBG_dump();
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#endif
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  return(0);
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}
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/* inspects the OggVorbis file and finds/documents all the logical
   bitstreams contained in it.  Tries to be tolerant of logical
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   bitstream sections that are truncated/woogie. 

   return: -1) error
            0) OK
*/

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int ov_open_callbacks(void *f,OggVorbis_File *vf,char *initial,long ibytes,
    ov_callbacks callbacks){
  int ret=_ov_open1(f,vf,initial,ibytes,callbacks);
  if(ret)return ret;
  return _ov_open2(vf);
}

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int ov_open(FILE *f,OggVorbis_File *vf,char *initial,long ibytes){
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  ov_callbacks callbacks = {
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    (size_t (*)(void *, size_t, size_t, void *))  fread,
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    (int (*)(void *, ogg_int64_t, int))              _fseek64_wrap,
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    (int (*)(void *))                             fclose,
    (long (*)(void *))                            ftell
  };
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  return ov_open_callbacks((void *)f, vf, initial, ibytes, callbacks);
}
  
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/* Only partially open the vorbis file; test for Vorbisness, and load
   the headers for the first chain.  Do not seek (although test for
   seekability).  Use ov_test_open to finish opening the file, else
   ov_clear to close/free it. Same return codes as open. */
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int ov_test_callbacks(void *f,OggVorbis_File *vf,char *initial,long ibytes,
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    ov_callbacks callbacks)
{
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  return _ov_open1(f,vf,initial,ibytes,callbacks);
}
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int ov_test(FILE *f,OggVorbis_File *vf,char *initial,long ibytes){
  ov_callbacks callbacks = {
    (size_t (*)(void *, size_t, size_t, void *))  fread,
    (int (*)(void *, ogg_int64_t, int))              _fseek64_wrap,
    (int (*)(void *))                             fclose,
    (long (*)(void *))                            ftell
  };
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  return ov_test_callbacks((void *)f, vf, initial, ibytes, callbacks);
}
  
int ov_test_open(OggVorbis_File *vf){
  if(vf->ready_state!=PARTOPEN)return(OV_EINVAL);
  return _ov_open2(vf);
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}

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/* How many logical bitstreams in this physical bitstream? */
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long ov_streams(OggVorbis_File *vf){
  return vf->links;
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}

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/* Is the FILE * associated with vf seekable? */
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long ov_seekable(OggVorbis_File *vf){
  return vf->seekable;
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}

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/* returns the bitrate for a given logical bitstream or the entire
   physical bitstream.  If the file is open for random access, it will
   find the *actual* average bitrate.  If the file is streaming, it
   returns the nominal bitrate (if set) else the average of the
   upper/lower bounds (if set) else -1 (unset).

   If you want the actual bitrate field settings, get them from the
   vorbis_info structs */

long ov_bitrate(OggVorbis_File *vf,int i){
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  if(vf->ready_state<OPENED)return(OV_EINVAL);
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  if(i>=vf->links)return(OV_EINVAL);
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  if(!vf->seekable && i!=0)return(ov_bitrate(vf,0));
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  if(i<0){
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    ogg_int64_t bits=0;
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    int i;
    for(i=0;i<vf->links;i++)
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      bits+=(vf->offsets[i+1]-vf->dataoffsets[i])*8;
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    return(rint(bits/ov_time_total(vf,-1)));
  }else{
    if(vf->seekable){
      /* return the actual bitrate */
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      return(rint((vf->offsets[i+1]-vf->dataoffsets[i])*8/ov_time_total(vf,i)));
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    }else{
      /* return nominal if set */
      if(vf->vi[i].bitrate_nominal>0){
	return vf->vi[i].bitrate_nominal;
      }else{
	if(vf->vi[i].bitrate_upper>0){
	  if(vf->vi[i].bitrate_lower>0){
	    return (vf->vi[i].bitrate_upper+vf->vi[i].bitrate_lower)/2;
	  }else{
	    return vf->vi[i].bitrate_upper;
	  }
	}
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	return(OV_FALSE);
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      }
    }
  }
}

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/* returns the actual bitrate since last call.  returns -1 if no
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   additional data to offer since last call (or at beginning of stream),
   EINVAL if stream is only partially open 
*/
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long ov_bitrate_instant(OggVorbis_File *vf){
  int link=(vf->seekable?vf->current_link:0);
  long ret;
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  if(vf->ready_state<OPENED)return(OV_EINVAL);
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  if(vf->samptrack==0)return(OV_FALSE);
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  ret=vf->bittrack/vf->samptrack*vf->vi[link].rate+.5;
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  vf->bittrack=0.f;
  vf->samptrack=0.f;
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  return(ret);
}

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/* Guess */
long ov_serialnumber(OggVorbis_File *vf,int i){
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  if(i>=vf->links)return(ov_serialnumber(vf,vf->links-1));
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  if(!vf->seekable && i>=0)return(ov_serialnumber(vf,-1));
  if(i<0){
    return(vf->current_serialno);
  }else{
    return(vf->serialnos[i]);
  }
}

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/* returns: total raw (compressed) length of content if i==-1
            raw (compressed) length of that logical bitstream for i==0 to n
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	    OV_EINVAL if the stream is not seekable (we can't know the length)
	    or if stream is only partially open
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*/
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ogg_int64_t ov_raw_total(OggVorbis_File *vf,int i){
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  if(vf->ready_state<OPENED)return(OV_EINVAL);
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  if(!vf->seekable || i>=vf->links)return(OV_EINVAL);
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  if(i<0){
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    long acc=0;
    int i;
    for(i=0;i<vf->links;i++)
      acc+=ov_raw_total(vf,i);
    return(acc);
  }else{
    return(vf->offsets[i+1]-vf->offsets[i]);
  }
}
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/* returns: total PCM length (samples) of content if i==-1 PCM length
	    (samples) of that logical bitstream for i==0 to n
	    OV_EINVAL if the stream is not seekable (we can't know the
	    length) or only partially open 
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*/
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ogg_int64_t ov_pcm_total(OggVorbis_File *vf,int i){
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  if(vf->ready_state<OPENED)return(OV_EINVAL);
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  if(!vf->seekable || i>=vf->links)return(OV_EINVAL);
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  if(i<0){
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    ogg_int64_t acc=0;
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    int i;
    for(i=0;i<vf->links;i++)
      acc+=ov_pcm_total(vf,i);
    return(acc);
  }else{
    return(vf->pcmlengths[i]);
  }
}
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/* returns: total seconds of content if i==-1
            seconds in that logical bitstream for i==0 to n
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	    OV_EINVAL if the stream is not seekable (we can't know the
	    length) or only partially open 
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*/
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double ov_time_total(OggVorbis_File *vf,int i){
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  if(vf->ready_state<OPENED)return(OV_EINVAL);
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  if(!vf->seekable || i>=vf->links)return(OV_EINVAL);
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  if(i<0){
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    double acc=0;
    int i;
    for(i=0;i<vf->links;i++)
      acc+=ov_time_total(vf,i);
    return(acc);
  }else{
    return((float)(vf->pcmlengths[i])/vf->vi[i].rate);
  }
}
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/* seek to an offset relative to the *compressed* data. This also
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   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 bitstream we seek to (so no surprises).
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   returns zero on success, nonzero on failure */
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int ov_raw_seek(OggVorbis_File *vf,long pos){
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  ogg_stream_state work_os;

  if(vf->ready_state<OPENED)return(OV_EINVAL);
  if(!vf->seekable)
    return(OV_ENOSEEK); /* don't dump machine if we can't seek */

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  if(pos<0 || pos>vf->offsets[vf->links])return(OV_EINVAL);
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  /* clear out decoding machine state */
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  vf->pcm_offset=-1;
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  _decode_clear(vf);
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  _seek_helper(vf,pos);

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  /* we need to make sure the pcm_offset is set, but we don't want to
     advance the raw cursor past good packets just to get to the first
     with a granulepos.  That's not equivalent behavior to beginning
     decoding as immediately after the seek position as possible.

     So, a hack.  We use two stream states; a local scratch state and
     a the shared vf->os stream state.  We use the local state to
     scan, and the shared state as a buffer for later decode. 

     Unfortuantely, on the last page we still advance to last packet
     because the granulepos on the last page is not necessarily on a
     packet boundary, and we need to make sure the granpos is
     correct. 
  */

  {
    ogg_page og;
    ogg_packet op;
    int lastblock=0;
    int accblock=0;
    int thisblock;
    int eosflag;

    memset(&work_os,0,sizeof(work_os));/* so that it's safe to clear
					  it later even if we don't
					  init it */

    while(1){
      if(vf->ready_state==STREAMSET){
	/* snarf/scan a packet if we can */
	int result=ogg_stream_packetout(&work_os,&op);
      
	if(result>0){

	  if(vf->vi[vf->current_link].codec_setup)
	    thisblock=vorbis_packet_blocksize(vf->vi+vf->current_link,&op);
	  if(eosflag)
	    ogg_stream_packetout(&vf->os,NULL);
	  else
	    if(lastblock)accblock+=(lastblock+thisblock)>>2;

	  if(op.granulepos!=-1){
	    int i,link=vf->current_link;
	    ogg_int64_t granulepos=op.granulepos;
	    
	    for(i=0;i<link;i++)
	      granulepos+=vf->pcmlengths[i];
	    vf->pcm_offset=granulepos-accblock;
	    break;
	  }
	  lastblock=thisblock;
	  continue;
	}
      }
      
      if(!lastblock){
	if(_get_next_page(vf,&og,-1)<0){
	  vf->pcm_offset=ov_pcm_total(vf,-1);
	  break;
	}
      }else{
	/* huh?  Bogus stream with packets but no granulepos */
	vf->pcm_offset=-1;
	break;
      }
      
      /* has our decoding just traversed a bitstream boundary? */
      if(vf->ready_state==STREAMSET)
	if(vf->current_serialno!=ogg_page_serialno(&og)){
	_decode_clear(vf); /* clear out stream state */
	ogg_stream_clear(&work_os);
      }

      if(vf->ready_state<STREAMSET){
	int link;
	
	vf->current_serialno=ogg_page_serialno(&og);
	for(link=0;link<vf->links;link++)
	  if(vf->serialnos[link]==vf->current_serialno)break;
	if(link==vf->links)goto seek_error; /* sign of a bogus stream.
					       error out, leave
					       machine uninitialized */
	vf->current_link=link;
	
	ogg_stream_init(&vf->os,vf->current_serialno);
	ogg_stream_reset(&vf->os); 
	ogg_stream_init(&work_os,vf->current_serialno);
	ogg_stream_reset(&work_os); 
	vf->ready_state=STREAMSET;
	
      }
    
      ogg_stream_pagein(&vf->os,&og);
      ogg_stream_pagein(&work_os,&og);
      eosflag=ogg_page_eos(&og);
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    }
  }
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  ogg_stream_clear(&work_os);
  return(0);

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 seek_error:
  /* dump the machine so we're in a known state */
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  vf->pcm_offset=-1;
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  ogg_stream_clear(&work_os);
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  _decode_clear(vf);
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  return OV_EBADLINK;
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}

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/* Page granularity seek (faster than sample granularity because we
   don't do the last bit of decode to find a specific sample).
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   Seek to the last [granule marked] page preceeding the specified pos
   location, such that decoding past the returned point will quickly
   arrive at the requested position. */
int ov_pcm_seek_page(OggVorbis_File *vf,ogg_int64_t pos){
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  int link=-1;
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  long ret;
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  ogg_int64_t total=ov_pcm_total(vf,-1);
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  if(vf->ready_state<OPENED)return(OV_EINVAL);
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  if(!vf->seekable)return(OV_ENOSEEK);
  if(pos<0 || pos>total)return(OV_EINVAL);
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  /* which bitstream section does this pcm offset occur in? */
  for(link=vf->links-1;link>=0;link--){
    total-=vf->pcmlengths[link];
    if(pos>=total)break;
  }

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  /* search within the logical bitstream for the page with the highest
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     pcm_pos preceeding (or equal to) pos.  There is a danger here;
     missing pages or incorrect frame number information in the
     bitstream could make our task impossible.  Account for that (it
     would be an error condition) */
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  /* new search algorithm by HB (Nicholas Vinen) */
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  {
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    ogg_int64_t target=pos-total;
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    long end=vf->offsets[link+1];
    long begin=vf->offsets[link];
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    ogg_int64_t endtime = vf->pcmlengths[link];
    ogg_int64_t begintime = 0;
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    long best=begin;
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    ogg_page og;
    while(begin<end){
      long bisect;
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      if(end-begin<CHUNKSIZE){
	bisect=begin;
      }else{
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	/* take a (pretty decent) guess. */
	bisect=begin + 
	  (target-begintime)*(end-begin)/(endtime-begintime) - CHUNKSIZE;
	if(bisect<=begin)
	  bisect=begin+1;
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      }
      _seek_helper(vf,bisect);
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