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[16]1<html>
2
3<head>
4<title>vorbisfile - 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>vorbisfile documentation</p></td>
12<td align=right><p class=tiny>vorbisfile version 1.25 - 20000615</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 vorbisfile - <a href="vorbisfile_example_c.html">vorbisfile_example.c</a>. 
21This program takes a vorbis bitstream from stdin and writes raw pcm to stdout.
22
23<p>
24First, relevant headers, including vorbis-specific "codec.h" and "vorbisfile.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 &lt;stdio.h&gt;
32#include &lt;stdlib.h&gt;
33#include &lt;math.h&gt;
34#include "vorbis/codec.h"
35#include "vorbis/vorbisfile.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 &lt;io.h&gt;
49#include &lt;fcntl.h&gt;
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#endif
84</b></pre>
85        </td>
86</tr>
87</table>
88
89<p><a href="ov_open_callbacks.html">ov_open_callbacks()</a> must be
90called to initialize the <b>OggVorbis_File</b> structure with default values. 
91<a href="ov_open_callbacks.html">ov_open_callbacks()</a> also checks to ensure that we're reading Vorbis format and not something else.
92
93<br><br>
94<table border=0 width=100% color=black cellspacing=0 cellpadding=7>
95<tr bgcolor=#cccccc>
96        <td>
97<pre><b>
98  if(ov_open_callbacks(stdin, &vf, NULL, 0, OV_CALLBACKS_NOCLOSE) < 0) {
99      fprintf(stderr,"Input does not appear to be an Ogg bitstream.\n");
100      exit(1);
101  }
102
103</b></pre>
104        </td>
105</tr>
106</table>
107
108<p>
109We'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.
110We also want to pull out and show the user a comment attached to the file using <a href="ov_comment.html">ov_comment()</a>.
111
112<br><br>
113<table border=0 width=100% color=black cellspacing=0 cellpadding=7>
114<tr bgcolor=#cccccc>
115        <td>
116<pre><b>
117  {
118    char **ptr=ov_comment(&vf,-1)->user_comments;
119    vorbis_info *vi=ov_info(&vf,-1);
120    while(*ptr){
121      fprintf(stderr,"%s\n",*ptr);
122      ++ptr;
123    }
124    fprintf(stderr,"\nBitstream is %d channel, %ldHz\n",vi->channels,vi->rate);
125    fprintf(stderr,"Encoded by: %s\n\n",ov_comment(&vf,-1)->vendor);
126  }
127 
128</b></pre>
129        </td>
130</tr>
131</table>
132
133<p>
134Here's the read loop:
135
136<br><br>
137<table border=0 width=100% color=black cellspacing=0 cellpadding=7>
138<tr bgcolor=#cccccc>
139        <td>
140<pre><b>
141
142  while(!eof){
143    long ret=ov_read(&vf,pcmout,sizeof(pcmout),0,2,1,&current_section);
144    switch(ret){
145    case 0:
146      /* EOF */
147      eof=1;
148      break;
149    case -1:
150      break;
151    default:
152      fwrite(pcmout,1,ret,stdout);
153      break;
154    }
155  }
156 
157</b></pre>
158        </td>
159</tr>
160</table>
161
162<p>
163The code is reading blocks of data using <a href="ov_read.html">ov_read()</a>.
164Based 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.
165
166<p>
167Now 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.
168
169<br><br>
170<table border=0 width=100% color=black cellspacing=0 cellpadding=7>
171<tr bgcolor=#cccccc>
172        <td>
173<pre><b>
174
175  ov_clear(&vf);
176   
177  fprintf(stderr,"Done.\n");
178  return(0);
179}
180</b></pre>
181        </td>
182</tr>
183</table>
184
185<p>
186The full source for vorbisfile_example.c can be found with the vorbis
187distribution in <a href="vorbisfile_example_c.html">vorbisfile_example.c</a>.
188
189<br><br>
190<hr noshade>
191<table border=0 width=100%>
192<tr valign=top>
193<td><p class=tiny>copyright &copy; 2000 vorbis team</p></td>
194<td align=right><p class=tiny><a href="http://www.xiph.org/ogg/vorbis/">Ogg Vorbis</a><br><a href="mailto:team@vorbis.org">team@vorbis.org</a></p></td>
195</tr><tr>
196<td><p class=tiny>vorbisfile documentation</p></td>
197<td align=right><p class=tiny>vorbisfile version 1.25 - 20000615</p></td>
198</tr>
199</table>
200
201</body>
202
203</html>
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