| 1 | <html> |
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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 1.2.0 - 20070723</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>. This |
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| 24 | function works similarly to reading from a normal file using |
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| 25 | <tt>read()</tt>.<p> |
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| 26 | |
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| 27 | However, a few differences are worth noting: |
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| 28 | |
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| 29 | <h2>multiple stream links</h2> |
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| 30 | |
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| 31 | A Vorbis stream may consist of multiple sections (called links) that |
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| 32 | encode differing numbers of channels or sample rates. It is vitally |
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| 33 | important to pay attention to the link numbers returned by <a |
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| 34 | href="ov_read.html">ov_read</a> and handle audio changes that may |
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| 35 | occur at link boundaries. Such multi-section files do exist in the |
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| 36 | wild and are not merely a specification curiosity. |
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| 37 | |
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| 38 | <h2>returned data amount</h2> |
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| 39 | |
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| 40 | <a href="ov_read.html">ov_read</a> does not attempt to completely fill |
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| 41 | a large, passed in data buffer; it merely guarantees that the passed |
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| 42 | back data does not overflow the passed in buffer size. Large buffers |
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| 43 | may be filled by iteratively looping over calls to <a |
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| 44 | href="ov_read.html">ov_read</a> (incrementing the buffer pointer) |
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| 45 | until the original buffer is filled. |
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| 46 | |
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| 47 | <h2>file cursor position</h2> |
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| 48 | |
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| 49 | Vorbis files do not necessarily start at a sample number or time offset |
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| 50 | of zero. Do not be surprised if a file begins at a positive offset of |
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| 51 | several minutes or hours, such as would happen if a large stream (such |
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| 52 | as a concert recording) is chopped into multiple seperate files. |
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| 53 | |
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| 54 | <p> |
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| 55 | <table border=1 color=black width=50% cellspacing=0 cellpadding=7> |
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| 56 | <tr bgcolor=#cccccc> |
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| 57 | <td><b>function</b></td> |
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| 58 | <td><b>purpose</b></td> |
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| 59 | </tr> |
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| 60 | <tr valign=top> |
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| 61 | <td><a href="ov_read.html">ov_read</a></td> |
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| 62 | <td>This function makes up the main chunk of a decode loop. It takes an |
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| 63 | OggVorbis_File structure, which must have been initialized by a previous |
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| 64 | 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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| 65 | or <a href="ov_open_callbacks.html"><tt>ov_open_callbacks()</tt></a>.</td> |
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| 66 | </tr> |
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| 67 | <tr valign=top> |
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| 68 | <td><a href="ov_read_float.html">ov_read_float</a></td> |
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| 69 | <td>This function decodes to floats instead of integer samples.</td> |
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| 70 | </tr> |
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| 71 | </table> |
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| 72 | |
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| 73 | <br><br> |
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| 74 | <hr noshade> |
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| 75 | <table border=0 width=100%> |
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| 76 | <tr valign=top> |
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| 77 | <td><p class=tiny>copyright © 2007 Xiph.org</p></td> |
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| 78 | <td align=right><p class=tiny><a href="http://www.xiph.org/ogg/vorbis/">Ogg Vorbis</a></p></td> |
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| 79 | </tr><tr> |
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| 80 | <td><p class=tiny>Vorbisfile documentation</p></td> |
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| 81 | <td align=right><p class=tiny>vorbisfile version 1.2.0 - 20070723</p></td> |
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| 82 | </tr> |
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| 83 | </table> |
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| 84 | |
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| 85 | </body> |
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| 86 | |
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| 87 | </html> |
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