1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
|
<html>
<head>
<title>vorbisfile - Example Code</title>
<link rel=stylesheet href="style.css" type="text/css">
</head>
<body bgcolor=white text=black link="#5555ff" alink="#5555ff" vlink="#5555ff">
<table border=0 width=100%>
<tr>
<td><p class=tiny>vorbisfile documentation</p></td>
<td align=right><p class=tiny>vorbisfile version 1.25 - 20000615</p></td>
</tr>
</table>
<h1>Example Code</h1>
<p>
The following is a run-through of the decoding example program supplied
with vorbisfile - <a href="vorbisfile_example_c.html">vorbisfile_example.c</a>.
This program takes a vorbis bitstream from stdin and writes raw pcm to stdout.
<p>
First, relevant headers, including vorbis-specific "codec.h" and "vorbisfile.h" have to be included.
<br><br>
<table border=0 width=100% color=black cellspacing=0 cellpadding=7>
<tr bgcolor=#cccccc>
<td>
<pre><b>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "vorbis/codec.h"
#include "vorbis/vorbisfile.h"
</b></pre>
</td>
</tr>
</table>
<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.
<br><br>
<table border=0 width=100% color=black cellspacing=0 cellpadding=7>
<tr bgcolor=#cccccc>
<td>
<pre><b>
#ifdef _WIN32
#include <io.h>
#include <fcntl.h>
#endif
</b></pre>
</td>
</tr>
</table>
<p>
Next, a buffer for the pcm audio output is declared.
<br><br>
<table border=0 width=100% color=black cellspacing=0 cellpadding=7>
<tr bgcolor=#cccccc>
<td>
<pre><b>
char pcmout[4096];
</b></pre>
</td>
</tr>
</table>
<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.
<br><br>
<table border=0 width=100% color=black cellspacing=0 cellpadding=7>
<tr bgcolor=#cccccc>
<td>
<pre><b>
int main(int argc, char **argv){
OggVorbis_File vf;
int eof=0;
int current_section;
#ifdef _WIN32
_setmode( _fileno( stdin ), _O_BINARY );
#endif
</b></pre>
</td>
</tr>
</table>
<p><a href="ov_open_callbacks.html">ov_open_callbacks()</a> must be
called 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.
<br><br>
<table border=0 width=100% color=black cellspacing=0 cellpadding=7>
<tr bgcolor=#cccccc>
<td>
<pre><b>
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);
}
</b></pre>
</td>
</tr>
</table>
<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>.
<br><br>
<table border=0 width=100% color=black cellspacing=0 cellpadding=7>
<tr bgcolor=#cccccc>
<td>
<pre><b>
{
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,"Encoded by: %s\n\n",ov_comment(&vf,-1)->vendor);
}
</b></pre>
</td>
</tr>
</table>
<p>
Here's the read loop:
<br><br>
<table border=0 width=100% color=black cellspacing=0 cellpadding=7>
<tr bgcolor=#cccccc>
<td>
<pre><b>
while(!eof){
long ret=ov_read(&vf,pcmout,sizeof(pcmout),0,2,1,&current_section);
switch(ret){
case 0:
/* EOF */
eof=1;
break;
case -1:
break;
default:
fwrite(pcmout,1,ret,stdout);
break;
}
}
</b></pre>
</td>
</tr>
</table>
<p>
The code is reading blocks of data using <a href="ov_read.html">ov_read()</a>.
Based 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.
<p>
Now 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.
<br><br>
<table border=0 width=100% color=black cellspacing=0 cellpadding=7>
<tr bgcolor=#cccccc>
<td>
<pre><b>
ov_clear(&vf);
fprintf(stderr,"Done.\n");
return(0);
}
</b></pre>
</td>
</tr>
</table>
<p>
The full source for vorbisfile_example.c can be found with the vorbis
distribution in <a href="vorbisfile_example_c.html">vorbisfile_example.c</a>.
<br><br>
<hr noshade>
<table border=0 width=100%>
<tr valign=top>
<td><p class=tiny>copyright © 2000 vorbis team</p></td>
<td align=right><p class=tiny><a href="http://www.xiph.org/ogg/vorbis/">Ogg Vorbis</a></p></td>
</tr><tr>
<td><p class=tiny>vorbisfile documentation</p></td>
<td align=right><p class=tiny>vorbisfile version 1.25 - 20000615</p></td>
</tr>
</table>
</body>
</html>
|
