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1 <html>
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3 <head>
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4 <title>libvorbis - API Overview</title>
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5 <link rel=stylesheet href="style.css" type="text/css">
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6 </head>
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7
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8 <body bgcolor=white text=black link="#5555ff" alink="#5555ff" vlink="#5555ff">
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9 <table border=0 width=100%>
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10 <tr>
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11 <td><p class=tiny>libvorbis documentation</p></td>
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12 <td align=right><p class=tiny>libvorbis version 1.3.2 - 20101101</p></td>
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13 </tr>
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14 </table>
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15
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16 <h1>Libvorbis API Overview</h1>
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17
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18 <p>Libvorbis is the reference implementation of the Vorbis codec. It is
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19 the lowest-level interface to the Vorbis encoder and decoder, working
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20 with packets directly.</p>
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21
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22 <p>All libvorbis routines and structures are declared in "vorbis/codec.h".</p>
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23
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24 <h2>Encoding workflow</h2>
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25
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26 <ol>
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27 <li>Initialize a <a href="vorbis_info.html">vorbis_info</a> structure
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28 by calling <a href="vorbis_info_init.html">vorbis_info_init</a> and
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29 then functions from <a href="../vorbisenc/index.html">libvorbisenc</a>
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30 on it.</li>
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31 <li>Initialize a <a href="vorbis_dsp_state.html">vorbis_dsp_state</a>
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32 for encoding based on the parameters in the vorbis_info by using <a
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33 href="vorbis_analysis_init.html">vorbis_analysis_init</a>.</li>
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34 <li>Initialize a <a href="vorbis_comment.html">vorbis_comment</a>
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35 structure using <a href="vorbis_comment_init.html">vorbis_comment_init</a>,
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36 populate it with any comments you wish to store in the stream, and call
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37 <a href="vorbis_analysis_headerout.html">vorbis_analysis_headerout</a> to
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38 get the three Vorbis stream header packets. Output the packets.</li>
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39 <li>Initialize a <a href="vorbis_block.html">vorbis_block</a> structure
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40 using <a href="vorbis_block_init.html">vorbis_block_init</a>.</li>
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41 <li>While there is more audio to encode:<ol>
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42 <li>Submit a chunk of audio data using <a
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43 href="vorbis_analysis_buffer.html">vorbis_analysis_buffer</a> and <a
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44 href="vorbis_analysis_wrote.html">vorbis_analysis_wrote</a>.</li>
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45 <li>Obtain all available blocks using <a
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46 href="vorbis_analysis_blockout.html">vorbis_analysis_blockout</a>
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47 in a loop. For each block obtained:<ol>
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48 <li>Encode the block into a packet (or prepare it for bitrate management)
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49 using <a href="vorbis_analysis.html">vorbis_analysis</a>. (It's a good
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50 idea to always pass the blocks through the bitrate
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51 management mechanism; more information is on the <a
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52 href="vorbis_analysis.html">vorbis_analysis</a> page. It does not affect
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53 the resulting packets unless you are actually using a bitrate-managed
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54 mode.)</li>
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55 <li>If you are using bitrate management, submit the block using <a
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56 href="vorbis_bitrate_addblock.html">vorbis_bitrate_addblock</a> and obtain
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57 packets using <a
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58 href="vorbis_bitrate_flushpacket.html">vorbis_bitrate_flushpacket</a>.</li>
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59 <li>Output any obtained packets.</li>
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60 </ol></li>
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61 </ol></li>
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62 <li>Submit an empty buffer to indicate the end of input; this will result
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63 in an end-of-stream packet after all encoding steps are done to it.</li>
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64 <li>Destroy the structures using the appropriate vorbis_*_clear routines.</li>
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65 </ol>
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66
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67 <h2>Decoding workflow</h2>
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68
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69 <em>Note: if you do not need to do anything more involved than just
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70 decoding the audio from an Ogg Vorbis file, you can use the far simpler
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71 <a href="../vorbisfile/index.html">libvorbisfile</a> interface, which
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72 will take care of all of the demuxing and low-level decoding operations
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73 (and even the I/O, if you want) for you.</em>
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74
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75 <ol>
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76 <li>When reading the header packets of an Ogg stream, you can use <a
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77 href="vorbis_synthesis_idheader.html">vorbis_synthesis_idheader</a> to
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78 check whether a stream might be Vorbis.</li>
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79 <li>Initialize a <a href="vorbis_info.html">vorbis_info</a> and a <a
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80 href="vorbis_comment.html">vorbis_comment</a> structure using the
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81 appropriate vorbis_*_init routines, then pass the first three packets
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82 from the stream (the Vorbis stream header packets) to <a
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83 href="vorbis_synthesis_headerin.html">vorbis_synthesis_headerin</a> in
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84 order. At this point, you can see the comments and basic parameters of
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85 the Vorbis stream.</li>
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86 <li>Initialize a <a href="vorbis_dsp_state.html">vorbis_dsp_state</a>
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87 for decoding based on the parameters in the vorbis_info by using <a
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88 href="vorbis_synthesis_init.html">vorbis_synthesis_init</a>.</li>
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89 <li>Initialize a <a href="vorbis_block.html">vorbis_block</a> structure
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90 using <a href="vorbis_block_init.html">vorbis_block_init</a>.</li>
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91 <li>While there are more packets to decode:<ol>
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92 <li>Decode the next packet into a block using <a
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93 href="vorbis_synthesis.html">vorbis_synthesis</a>.</li>
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94 <li>Submit the block to the reassembly layer using <a
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95 href="vorbis_synthesis_blockin.html">vorbis_synthesis_blockin</a>.</li>
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96 <li>Obtain some decoded audio using <a
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97 href="vorbis_synthesis_pcmout.html">vorbis_synthesis_pcmout</a> and <a
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98 href="vorbis_synthesis_read.html">vorbis_synthesis_read</a>. Any audio data
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99 returned but not marked as consumed using vorbis_synthesis_read carries
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100 over to the next call to vorbis_synthesis_pcmout.</li>
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101 </ol></li>
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102 <li>Destroy the structures using the appropriate vorbis_*_clear routines.</li>
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103 </ol>
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104
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105 <h2>Metadata workflow</h2>
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106
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107 <em>Note: if you do not need to do anything more involved than just
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108 reading the metadata from an Ogg Vorbis file, <a
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109 href="../vorbisfile/index.html">libvorbisfile</a> can do this for you.</em>
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110
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111 <ol>
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112 <li>Follow the decoding workflow above until you have access to the comments
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113 and basic parameters of the Vorbis stream.</li>
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114 <li>If you want to alter the comments, copy the first packet to the output
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115 file, then create a packet for the modified comments using <a
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116 href="vorbis_commentheader_out.html">vorbis_commentheader_out</a> and output
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117 it, then copy the third packet and all subsequent packets into the output
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118 file.</li>
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119 </ol>
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120
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121 <br><br>
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122 <hr noshade>
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123 <table border=0 width=100%>
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124 <tr valign=top>
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125 <td><p class=tiny>copyright © 2010 Xiph.Org</p></td>
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126 <td align=right><p class=tiny><a href="http://www.xiph.org/ogg/vorbis/index.html">Ogg Vorbis</a></p></td>
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127 </tr><tr>
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128 <td><p class=tiny>libvorbis documentation</p></td>
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129 <td align=right><p class=tiny>libvorbis version 1.3.2 - 20101101</p></td>
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130 </tr>
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131 </table>
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132
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133 </body>
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134
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135 </html>
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136
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