doc/vorbisfile/example.html

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<title>Vorbisfile - Example Code</title>
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<td><p class=tiny>Vorbisfile documentation</p></td>
<td align=right><p class=tiny>vorbisfile version 1.2.0 - 20070723</p></td>
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<h1>Decoding Example Code</h1>

<p>
The following is a run-through of the decoding example program supplied
with libvorbisfile, <a href="vorbisfile_example_c.html">vorbisfile_example.c</a>.
This program takes a vorbis bitstream from stdin and writes raw pcm to stdout.

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First, relevant headers, including vorbis-specific "vorbis/codec.h" and "vorbisfile.h" have to be included.

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#include &lt;stdio.h&gt;
#include &lt;stdlib.h&gt;
#include &lt;math.h&gt;
#include "vorbis/codec.h"
#include "vorbisfile.h"
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<p>
We also have to make a concession to Windows users here.  If we are using windows for decoding, we must declare these libraries so that we can set stdin/stdout to binary.
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#ifdef _WIN32
#include &lt;io.h&gt;
#include &lt;fcntl.h&gt;
#endif
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<p>
Next, a buffer for the pcm audio output is declared.

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char pcmout[4096];
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<p>Inside main(), we declare our primary OggVorbis_File structure.  We also declare a few other helpful variables to track out progress within the file.
Also, we make our final concession to Windows users by setting the stdin and stdout to binary mode.
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int main(int argc, char **argv){
  OggVorbis_File vf;
  int eof=0;
  int current_section;

#ifdef _WIN32
  _setmode( _fileno( stdin ), _O_BINARY );
  _setmode( _fileno( stdout ), _O_BINARY );
#endif
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<p>We call <a href="ov_open_callbacks.html">ov_open_callbacks()</a> to
initialize the <b>OggVorbis_File</b> structure with default values.
<a href="ov_open_callbacks.html">ov_open_callbacks()</a> also checks
to ensure that we're reading Vorbis format and not something else. The
OV_CALLBACKS_NOCLOSE callbacks instruct libvorbisfile not to close
stdin later during cleanup.

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  if(ov_open_callbacks(stdin, &vf, NULL, 0, OV_CALLBACKS_NOCLOSE) < 0) {
      fprintf(stderr,"Input does not appear to be an Ogg bitstream.\n");
      exit(1);
  }

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<p>
We're going to pull the channel and bitrate info from the file using <a href="ov_info.html">ov_info()</a> and show them to the user.
We also want to pull out and show the user a comment attached to the file using <a href="ov_comment.html">ov_comment()</a>.

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  {
    char **ptr=ov_comment(&vf,-1)->user_comments;
    vorbis_info *vi=ov_info(&vf,-1);
    while(*ptr){
      fprintf(stderr,"%s\n",*ptr);
      ++ptr;
    }
    fprintf(stderr,"\nBitstream is %d channel, %ldHz\n",vi->channels,vi->rate);
    fprintf(stderr,"\nDecoded length: %ld samples\n",
            (long)ov_pcm_total(&vf,-1));
    fprintf(stderr,"Encoded by: %s\n\n",ov_comment(&vf,-1)->vendor);
  }

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<p>
Here's the read loop:

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  while(!eof){
    long ret=ov_read(&vf,pcmout,sizeof(pcmout),0,2,1,&current_section);
    if (ret == 0) {
      /* EOF */
      eof=1;
    } else if (ret < 0) {
      /* error in the stream.  Not a problem, just reporting it in
	 case we (the app) cares.  In this case, we don't. */
    } else {
      /* we don't bother dealing with sample rate changes, etc, but
	 you'll have to*/
      fwrite(pcmout,1,ret,stdout);
    }
  }