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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 1.2.0 - 20070723</p></td>
13</tr>
14</table>
15
16<h1>Decoding Example Code</h1>
17
18<p>
19The following is a run-through of the decoding example program supplied
20with libvorbisfile, vorbisfile_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 "vorbis/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 "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  _setmode( _fileno( stdout ), _O_BINARY );
84#endif
85</b></pre>
86        </td>
87</tr>
88</table>
89
90<p>We call <a href="ov_open_callbacks.html">ov_open_callbacks()</a> to
91initialize the <b>OggVorbis_File</b> structure with default values.
92<a href="ov_open_callbacks.html">ov_open_callbacks()</a> also checks
93to ensure that we're reading Vorbis format and not something else. The
94OV_CALLBACKS_NOCLOSE callbacks instruct libvorbisfile not to close
95stdin later during cleanup.
96
97<br><br>
98<table border=0 width=100% color=black cellspacing=0 cellpadding=7>
99<tr bgcolor=#cccccc>
100        <td>
101<pre><b>
102  if(ov_open_callbacks(stdin, &vf, NULL, 0, OV_CALLBACKS_NOCLOSE) < 0) {
103      fprintf(stderr,"Input does not appear to be an Ogg bitstream.\n");
104      exit(1);
105  }
106
107</b></pre>
108        </td>
109</tr>
110</table>
111
112<p>
113We'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.
114We also want to pull out and show the user a comment attached to the file using <a href="ov_comment.html">ov_comment()</a>.
115
116<br><br>
117<table border=0 width=100% color=black cellspacing=0 cellpadding=7>
118<tr bgcolor=#cccccc>
119        <td>
120<pre><b>
121  {
122    char **ptr=ov_comment(&vf,-1)->user_comments;
123    vorbis_info *vi=ov_info(&vf,-1);
124    while(*ptr){
125      fprintf(stderr,"%s\n",*ptr);
126      ++ptr;
127    }
128    fprintf(stderr,"\nBitstream is %d channel, %ldHz\n",vi->channels,vi->rate);
129    fprintf(stderr,"\nDecoded length: %ld samples\n",
130            (long)ov_pcm_total(&vf,-1));
131    fprintf(stderr,"Encoded by: %s\n\n",ov_comment(&vf,-1)->vendor);
132  }
133 
134</b></pre>
135        </td>
136</tr>
137</table>
138
139<p>
140Here's the read loop:
141
142<br><br>
143<table border=0 width=100% color=black cellspacing=0 cellpadding=7>
144<tr bgcolor=#cccccc>
145        <td>
146<pre><b>
147
148  while(!eof){
149    long ret=ov_read(&vf,pcmout,sizeof(pcmout),0,2,1,&current_section);
150    if (ret == 0) {
151      /* EOF */
152      eof=1;
153    } else if (ret < 0) {
154      /* error in the stream.  Not a problem, just reporting it in
155         case we (the app) cares.  In this case, we don't. */
156    } else {
157      /* we don't bother dealing with sample rate changes, etc, but
158         you'll have to*/
159      fwrite(pcmout,1,ret,stdout);
160    }
161  }
162
163 
164</b></pre>
165        </td>
166</tr>
167</table>
168
169<p>
170The code is reading blocks of data using <a href="ov_read.html">ov_read()</a>.
171Based 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.
172
173<p>
174Now 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.
175
176<br><br>
177<table border=0 width=100% color=black cellspacing=0 cellpadding=7>
178<tr bgcolor=#cccccc>
179        <td>
180<pre><b>
181
182  ov_clear(&vf);
183   
184  fprintf(stderr,"Done.\n");
185  return(0);
186}
187</b></pre>
188        </td>
189</tr>
190</table>
191
192<p>
193
194<br><br>
195<hr noshade>
196<table border=0 width=100%>
197<tr valign=top>
198<td><p class=tiny>copyright &copy; 2007 Xiph.org</p></td>
199<td align=right><p class=tiny><a href="http://www.xiph.org/ogg/vorbis/">Ogg Vorbis</a></p></td>
200</tr><tr>
201<td><p class=tiny>Vorbisfile documentation</p></td>
202<td align=right><p class=tiny>vorbisfile version 1.2.0 - 20070723</p></td>
203</tr>
204</table>
205
206</body>
207
208</html>
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