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| 2 |
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| 3 | <head>
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| 4 | <title>Vorbisfile - Decoding</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>Vorbisfile documentation</p></td>
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| 12 | <td align=right><p class=tiny>vorbisfile 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>Decoding</h1>
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| 17 |
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| 18 | <p>
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| 19 | All libvorbisfile decoding routines are declared in "vorbis/vorbisfile.h".
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| 20 | <p>
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| 21 |
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| 22 | After <a href="initialization.html">initialization</a>, decoding audio
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| 23 | is as simple as calling <a href="ov_read.html">ov_read()</a> (or the
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| 24 | similar functions <a href="ov_read_float.html">ov_read_float()</a> and
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| 25 | <a href="ov_read_filter.html">ov_read_filter</a>). This function works
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| 26 | similarly to reading from a normal file using <tt>read()</tt>.<p>
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| 27 |
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| 28 | However, a few differences are worth noting:
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| 29 |
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| 30 | <h2>multiple stream links</h2>
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| 31 |
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| 32 | A Vorbis stream may consist of multiple sections (called links) that
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| 33 | encode differing numbers of channels or sample rates. It is vitally
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| 34 | important to pay attention to the link numbers returned by <a
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| 35 | href="ov_read.html">ov_read</a> and handle audio changes that may
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| 36 | occur at link boundaries. Such multi-section files do exist in the
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| 37 | wild and are not merely a specification curiosity.
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| 38 |
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| 39 | <h2>returned data amount</h2>
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| 40 |
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| 41 | <a href="ov_read.html">ov_read</a> does not attempt to completely fill
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| 42 | a large, passed in data buffer; it merely guarantees that the passed
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| 43 | back data does not overflow the passed in buffer size. Large buffers
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| 44 | may be filled by iteratively looping over calls to <a
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| 45 | href="ov_read.html">ov_read</a> (incrementing the buffer pointer)
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| 46 | until the original buffer is filled.
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| 47 |
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| 48 | <h2>file cursor position</h2>
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| 49 |
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| 50 | Vorbis files do not necessarily start at a sample number or time offset
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| 51 | of zero. Do not be surprised if a file begins at a positive offset of
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| 52 | several minutes or hours, such as would happen if a large stream (such
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| 53 | as a concert recording) is chopped into multiple seperate files.
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| 54 |
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| 55 | <p>
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| 56 | <table border=1 color=black width=50% cellspacing=0 cellpadding=7>
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| 57 | <tr bgcolor=#cccccc>
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| 58 | <td><b>function</b></td>
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| 59 | <td><b>purpose</b></td>
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| 60 | </tr>
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| 61 | <tr valign=top>
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| 62 | <td><a href="ov_read.html">ov_read</a></td>
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| 63 | <td>This function makes up the main chunk of a decode loop. It takes an
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| 64 | OggVorbis_File structure, which must have been initialized by a previous
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| 65 | call to <a href="ov_open.html"><tt>ov_open()</tt></a>, <a href="ov_fopen.html"><tt>ov_fopen()</tt></a>,
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| 66 | or <a href="ov_open_callbacks.html"><tt>ov_open_callbacks()</tt></a>.</td>
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| 67 | </tr>
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| 68 | <tr valign=top>
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| 69 | <td><a href="ov_read_float.html">ov_read_float</a></td>
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| 70 | <td>This function decodes to floats instead of integer samples.</td>
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| 71 | </tr>
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| 72 | <tr valign=top>
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| 73 | <td><a href="ov_read_filter.html">ov_read_filter</a></td>
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| 74 | <td>This function works like <a href="ov_read.html">ov_read</a>, but passes the PCM data through the provided filter before converting to integer sample data.</td>
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| 75 | </tr>
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| 76 | </table>
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| 77 |
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| 78 | <br><br>
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| 79 | <hr noshade>
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| 80 | <table border=0 width=100%>
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| 81 | <tr valign=top>
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| 82 | <td><p class=tiny>copyright © 2000-2010 Xiph.Org</p></td>
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| 83 | <td align=right><p class=tiny><a href="https://xiph.org/vorbis/">Ogg Vorbis</a></p></td>
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| 84 | </tr><tr>
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| 85 | <td><p class=tiny>Vorbisfile documentation</p></td>
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| 86 | <td align=right><p class=tiny>vorbisfile version 1.3.2 - 20101101</p></td>
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| 87 | </tr>
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| 88 | </table>
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| 89 |
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| 90 | </body>
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| 91 |
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| 92 | </html>
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