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The Android Open Source Project43db9a82009-03-03 19:30:49 -0800[diff] [blame]1<html>
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3<head>
4<title>Tremor - Example Code</title>
5<link rel=stylesheet href="style.css" type="text/css">
6</head>
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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 &lt;stdio.h&gt;
32#include &lt;stdlib.h&gt;
33#include &lt;math.h&gt;
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 &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><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),&current_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 &copy; 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>