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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 1.3.2 - 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="http://www.xiph.org/ogg/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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