1<html> 2 3<head> 4<title>Tremor - Example Code</title> 5<link rel=stylesheet href="style.css" type="text/css"> 6</head> 7 8<body bgcolor=white text=black link="#5555ff" alink="#5555ff" vlink="#5555ff"> 9<table border=0 width=100%> 10<tr> 11<td><p class=tiny>Tremor documentation</p></td> 12<td align=right><p class=tiny>Tremor version 1.0 - 20020403</p></td> 13</tr> 14</table> 15 16<h1>Example Code</h1> 17 18<p> 19The following is a run-through of the decoding example program supplied 20with libvorbisidec, ivorbisfile_example.c. 21This program takes a vorbis bitstream from stdin and writes raw pcm to stdout. 22 23<p> 24First, relevant headers, including vorbis-specific "ivorbiscodec.h" and "ivorbisfile.h" have to be included. 25 26<br><br> 27<table border=0 width=100% color=black cellspacing=0 cellpadding=7> 28<tr bgcolor=#cccccc> 29 <td> 30<pre><b> 31#include <stdio.h> 32#include <stdlib.h> 33#include <math.h> 34#include "ivorbiscodec.h" 35#include "ivorbisfile.h" 36</b></pre> 37 </td> 38</tr> 39</table> 40<p> 41We 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. 42<br><br> 43<table border=0 width=100% color=black cellspacing=0 cellpadding=7> 44<tr bgcolor=#cccccc> 45 <td> 46<pre><b> 47#ifdef _WIN32 48#include <io.h> 49#include <fcntl.h> 50#endif 51</b></pre> 52 </td> 53</tr> 54</table> 55<p> 56Next, a buffer for the pcm audio output is declared. 57 58<br><br> 59<table border=0 width=100% color=black cellspacing=0 cellpadding=7> 60<tr bgcolor=#cccccc> 61 <td> 62<pre><b> 63char pcmout[4096]; 64</b></pre> 65 </td> 66</tr> 67</table> 68 69<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. 70Also, we make our final concession to Windows users by setting the stdin and stdout to binary mode. 71<br><br> 72<table border=0 width=100% color=black cellspacing=0 cellpadding=7> 73<tr bgcolor=#cccccc> 74 <td> 75<pre><b> 76int main(int argc, char **argv){ 77 OggVorbis_File vf; 78 int eof=0; 79 int current_section; 80 81#ifdef _WIN32 82 _setmode( _fileno( stdin ), _O_BINARY ); 83 _setmode( _fileno( stdout ), _O_BINARY ); 84#endif 85</b></pre> 86 </td> 87</tr> 88</table> 89 90<p><a href="ov_open.html">ov_open()</a> must be 91called to initialize the <b>OggVorbis_File</b> structure with default values. 92<a href="ov_open.html">ov_open()</a> also checks to ensure that we're reading Vorbis format and not something else. 93 94<br><br> 95<table border=0 width=100% color=black cellspacing=0 cellpadding=7> 96<tr bgcolor=#cccccc> 97 <td> 98<pre><b> 99 if(ov_open(stdin, &vf, NULL, 0) < 0) { 100 fprintf(stderr,"Input does not appear to be an Ogg bitstream.\n"); 101 exit(1); 102 } 103 104</b></pre> 105 </td> 106</tr> 107</table> 108 109<p> 110We'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. 111We also want to pull out and show the user a comment attached to the file using <a href="ov_comment.html">ov_comment()</a>. 112 113<br><br> 114<table border=0 width=100% color=black cellspacing=0 cellpadding=7> 115<tr bgcolor=#cccccc> 116 <td> 117<pre><b> 118 { 119 char **ptr=ov_comment(&vf,-1)->user_comments; 120 vorbis_info *vi=ov_info(&vf,-1); 121 while(*ptr){ 122 fprintf(stderr,"%s\n",*ptr); 123 ++ptr; 124 } 125 fprintf(stderr,"\nBitstream is %d channel, %ldHz\n",vi->channels,vi->rate); 126 fprintf(stderr,"\nDecoded length: %ld samples\n", 127 (long)ov_pcm_total(&vf,-1)); 128 fprintf(stderr,"Encoded by: %s\n\n",ov_comment(&vf,-1)->vendor); 129 } 130 131</b></pre> 132 </td> 133</tr> 134</table> 135 136<p> 137Here's the read loop: 138 139<br><br> 140<table border=0 width=100% color=black cellspacing=0 cellpadding=7> 141<tr bgcolor=#cccccc> 142 <td> 143<pre><b> 144 145 while(!eof){ 146 long ret=ov_read(&vf,pcmout,sizeof(pcmout),¤t_section); 147 if (ret == 0) { 148 /* EOF */ 149 eof=1; 150 } else if (ret < 0) { 151 /* error in the stream. Not a problem, just reporting it in 152 case we (the app) cares. In this case, we don't. */ 153 } else { 154 /* we don't bother dealing with sample rate changes, etc, but 155 you'll have to*/ 156 fwrite(pcmout,1,ret,stdout); 157 } 158 } 159 160 161</b></pre> 162 </td> 163</tr> 164</table> 165 166<p> 167The code is reading blocks of data using <a href="ov_read.html">ov_read()</a>. 168Based on the value returned, we know if we're at the end of the file or have invalid data. If we have valid data, we write it to the pcm output. 169 170<p> 171Now that we've finished playing, we can pack up and go home. It's important to call <a href="ov_clear.html">ov_clear()</a> when we're finished. 172 173<br><br> 174<table border=0 width=100% color=black cellspacing=0 cellpadding=7> 175<tr bgcolor=#cccccc> 176 <td> 177<pre><b> 178 179 ov_clear(&vf); 180 181 fprintf(stderr,"Done.\n"); 182 return(0); 183} 184</b></pre> 185 </td> 186</tr> 187</table> 188 189<p> 190 191<br><br> 192<hr noshade> 193<table border=0 width=100%> 194<tr valign=top> 195<td><p class=tiny>copyright © 2002 Xiph.org</p></td> 196<td align=right><p class=tiny><a href="http://www.xiph.org/ogg/vorbis/">Ogg Vorbis</a></p></td> 197</tr><tr> 198<td><p class=tiny>Tremor documentation</p></td> 199<td align=right><p class=tiny>Tremor version 1.0 - 20020403</p></td> 200</tr> 201</table> 202 203</body> 204 205</html> 206