summaryrefslogtreecommitdiffhomepage
path: root/vorbis/doc/libvorbis/overview.html
blob: 22cd18645a8f1e2eb5e4f3c80731ca70cbd45d3b (plain)
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
<html>

<head>
<title>libvorbis - API Overview</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>libvorbis documentation</p></td>
<td align=right><p class=tiny>libvorbis version 1.3.2 - 20101101</p></td>
</tr>
</table>

<h1>Libvorbis API Overview</h1>

<p>Libvorbis is the reference implementation of the Vorbis codec. It is
the lowest-level interface to the Vorbis encoder and decoder, working
with packets directly.</p>

<p>All libvorbis routines and structures are declared in "vorbis/codec.h".</p>

<h2>Encoding workflow</h2>

<ol>
<li>Initialize a <a href="vorbis_info.html">vorbis_info</a> structure
by calling <a href="vorbis_info_init.html">vorbis_info_init</a> and
then functions from <a href="../vorbisenc/index.html">libvorbisenc</a>
on it.</li>
<li>Initialize a <a href="vorbis_dsp_state.html">vorbis_dsp_state</a>
for encoding based on the parameters in the vorbis_info by using <a
href="vorbis_analysis_init.html">vorbis_analysis_init</a>.</li>
<li>Initialize a <a href="vorbis_comment.html">vorbis_comment</a>
structure using <a href="vorbis_comment_init.html">vorbis_comment_init</a>,
populate it with any comments you wish to store in the stream, and call
<a href="vorbis_analysis_headerout.html">vorbis_analysis_headerout</a> to
get the three Vorbis stream header packets. Output the packets.</li>
<li>Initialize a <a href="vorbis_block.html">vorbis_block</a> structure
using <a href="vorbis_block_init.html">vorbis_block_init</a>.</li>
<li>While there is more audio to encode:<ol>
<li>Submit a chunk of audio data using <a
href="vorbis_analysis_buffer.html">vorbis_analysis_buffer</a> and <a
href="vorbis_analysis_wrote.html">vorbis_analysis_wrote</a>.</li>
<li>Obtain all available blocks using <a
href="vorbis_analysis_blockout.html">vorbis_analysis_blockout</a>
in a loop. For each block obtained:<ol>
<li>Encode the block into a packet (or prepare it for bitrate management)
using <a href="vorbis_analysis.html">vorbis_analysis</a>. (It's a good
idea to always pass the blocks through the bitrate
management mechanism; more information is on the <a
href="vorbis_analysis.html">vorbis_analysis</a> page. It does not affect
the resulting packets unless you are actually using a bitrate-managed
mode.)</li>
<li>If you are using bitrate management, submit the block using <a
href="vorbis_bitrate_addblock.html">vorbis_bitrate_addblock</a> and obtain
packets using <a
href="vorbis_bitrate_flushpacket.html">vorbis_bitrate_flushpacket</a>.</li>
<li>Output any obtained packets.</li>
</ol></li>
</ol></li>
<li>Submit an empty buffer to indicate the end of input; this will result
in an end-of-stream packet after all encoding steps are done to it.</li>
<li>Destroy the structures using the appropriate vorbis_*_clear routines.</li>
</ol>

<h2>Decoding workflow</h2>

<em>Note: if you do not need to do anything more involved than just
decoding the audio from an Ogg Vorbis file, you can use the far simpler
<a href="../vorbisfile/index.html">libvorbisfile</a> interface, which
will take care of all of the demuxing and low-level decoding operations
(and even the I/O, if you want) for you.</em>

<ol>
<li>When reading the header packets of an Ogg stream, you can use <a
href="vorbis_synthesis_idheader.html">vorbis_synthesis_idheader</a> to
check whether a stream might be Vorbis.</li>
<li>Initialize a <a href="vorbis_info.html">vorbis_info</a> and a <a
href="vorbis_comment.html">vorbis_comment</a> structure using the
appropriate vorbis_*_init routines, then pass the first three packets
from the stream (the Vorbis stream header packets) to <a
href="vorbis_synthesis_headerin.html">vorbis_synthesis_headerin</a> in
order. At this point, you can see the comments and basic parameters of
the Vorbis stream.</li>
<li>Initialize a <a href="vorbis_dsp_state.html">vorbis_dsp_state</a>
for decoding based on the parameters in the vorbis_info by using <a
href="vorbis_synthesis_init.html">vorbis_synthesis_init</a>.</li>
<li>Initialize a <a href="vorbis_block.html">vorbis_block</a> structure
using <a href="vorbis_block_init.html">vorbis_block_init</a>.</li>
<li>While there are more packets to decode:<ol>
<li>Decode the next packet into a block using <a
href="vorbis_synthesis.html">vorbis_synthesis</a>.</li>
<li>Submit the block to the reassembly layer using <a
href="vorbis_synthesis_blockin.html">vorbis_synthesis_blockin</a>.</li>
<li>Obtain some decoded audio using <a
href="vorbis_synthesis_pcmout.html">vorbis_synthesis_pcmout</a> and <a
href="vorbis_synthesis_read.html">vorbis_synthesis_read</a>. Any audio data
returned but not marked as consumed using vorbis_synthesis_read carries
over to the next call to vorbis_synthesis_pcmout.</li>
</ol></li>
<li>Destroy the structures using the appropriate vorbis_*_clear routines.</li>
</ol>

<h2>Metadata workflow</h2>

<em>Note: if you do not need to do anything more involved than just
reading the metadata from an Ogg Vorbis file, <a
href="../vorbisfile/index.html">libvorbisfile</a> can do this for you.</em>

<ol>
<li>Follow the decoding workflow above until you have access to the comments
and basic parameters of the Vorbis stream.</li>
<li>If you want to alter the comments, copy the first packet to the output
file, then create a packet for the modified comments using <a
href="vorbis_commentheader_out.html">vorbis_commentheader_out</a> and output
it, then copy the third packet and all subsequent packets into the output
file.</li>
</ol>

<br><br>
<hr noshade>
<table border=0 width=100%>
<tr valign=top>
<td><p class=tiny>copyright &copy; 2010 Xiph.Org</p></td>
<td align=right><p class=tiny><a href="http://www.xiph.org/ogg/vorbis/index.html">Ogg Vorbis</a></p></td>
</tr><tr>
<td><p class=tiny>libvorbis documentation</p></td>
<td align=right><p class=tiny>libvorbis version 1.3.2 - 20101101</p></td>
</tr>
</table>

</body>

</html>