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| 2 |
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| 3 | <head>
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| 4 | <title>Vorbisfile - function - ov_read</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>ov_read()</h1>
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| 17 |
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| 18 | <p><i>declared in "vorbis/vorbisfile.h";</i></p>
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| 19 |
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| 20 | <p>
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| 21 | This is the main function used to decode a Vorbis file within a
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| 22 | loop. It returns up to the specified number of bytes of decoded PCM audio
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| 23 | in the requested endianness, signedness, and word size. If the audio is
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| 24 | multichannel, the channels are interleaved in the output buffer.
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| 25 | If the passed in buffer is large, <tt>ov_read()</tt> will not fill
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| 26 | it; the passed in buffer size is treated as a <em>limit</em> and
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| 27 | not a request.
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| 28 |
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| 29 | <p>The output channels are in stream order and not remapped. Vorbis I
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| 30 | defines channel order as follows:
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| 31 |
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| 32 | <ul>
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| 33 | <li>one channel - the stream is monophonic
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| 34 | <li>two channels - the stream is stereo. channel order: left, right
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| 35 | <li>three channels - the stream is a 1d-surround encoding. channel order: left,
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| 36 | center, right
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| 37 | <li>four channels - the stream is quadraphonic surround. channel order: front left,
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| 38 | front right, rear left, rear right
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| 39 | <li>five channels - the stream is five-channel surround. channel order: front left,
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| 40 | center, front right, rear left, rear right
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| 41 | <li>six channels - the stream is 5.1 surround. channel order: front left, center,
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| 42 | front right, rear left, rear right, LFE
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| 43 | <li>seven channels - the stream is 6.1 surround. channel order: front left, center,
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| 44 | front right, side left, side right, rear center, LFE
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| 45 | <li>eight channels - the stream is 7.1 surround. channel order: front left, center,
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| 46 | front right, side left, side right, rear left, rear right,
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| 47 | LFE
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| 48 | <li>greater than eight channels - channel use and order is undefined
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| 49 | </ul>
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| 50 |
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| 51 | <p>Note that up to this point, the Vorbisfile API could more or less hide the
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| 52 | multiple logical bitstream nature of chaining from the toplevel
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| 53 | application if the toplevel application didn't particularly care.
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| 54 | However, when reading audio back, the application must be aware
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| 55 | that multiple bitstream sections do not necessarily use the same
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| 56 | number of channels or sampling rate. <p> <tt>ov_read()</tt> passes
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| 57 | back the index of the sequential logical bitstream currently being
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| 58 | decoded (in <tt>*bitstream</tt>) along with the PCM data in order
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| 59 | that the toplevel application can handle channel and/or sample
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| 60 | rate changes. This number will be incremented at chaining
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| 61 | boundaries even for non-seekable streams. For seekable streams, it
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| 62 | represents the actual chaining index within the physical bitstream.
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| 63 | <p>
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| 64 |
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| 65 | <br><br>
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| 66 | <table border=0 color=black cellspacing=0 cellpadding=7>
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| 67 | <tr bgcolor=#cccccc>
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| 68 | <td>
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| 69 | <pre><b>
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| 70 | long ov_read(<a href="OggVorbis_File.html">OggVorbis_File</a> *vf, char *buffer, int length, int bigendianp, int word, int sgned, int *bitstream);
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| 71 | </b></pre>
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| 72 | </td>
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| 73 | </tr>
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| 74 | </table>
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| 75 |
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| 76 | <h3>Parameters</h3>
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| 77 | <dl>
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| 78 | <dt><i>vf</i></dt>
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| 79 | <dd>A pointer to the OggVorbis_File structure--this is used for ALL the externally visible libvorbisfile
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| 80 | functions.</dd>
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| 81 | <dt><i>buffer</i></dt>
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| 82 | <dd>A pointer to an output buffer. The decoded output is inserted into this buffer.</dd>
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| 83 | <dt><i>length</i></dt>
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| 84 | <dd>Number of bytes to be read into the buffer. Should be the same size as the buffer. A typical value is 4096.</dd>
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| 85 | <dt><i>bigendianp</i></dt>
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| 86 | <dd>Specifies big or little endian byte packing. 0 for little endian, 1 for b
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| 87 | ig endian. Typical value is 0.</dd>
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| 88 | <dt><i>word</i></dt>
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| 89 | <dd>Specifies word size. Possible arguments are 1 for 8-bit samples, or 2 or
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| 90 | 16-bit samples. Typical value is 2.</dd>
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| 91 | <dt><i>sgned</i></dt>
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| 92 | <dd>Signed or unsigned data. 0 for unsigned, 1 for signed. Typically 1.</dd>
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| 93 | <dt><i>bitstream</i></dt>
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| 94 | <dd>A pointer to the number of the current logical bitstream.</dd>
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| 95 | </dl>
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| 96 |
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| 97 |
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| 98 | <h3>Return Values</h3>
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| 99 | <blockquote>
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| 100 | <dl>
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| 101 | <dt>OV_HOLE</dt>
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| 102 | <dd>indicates there was an interruption in the data.
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| 103 | <br>(one of: garbage between pages, loss of sync followed by
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| 104 | recapture, or a corrupt page)</dd>
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| 105 | <dt>OV_EBADLINK</dt>
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| 106 | <dd>indicates that an invalid stream section was supplied to
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| 107 | libvorbisfile, or the requested link is corrupt.</dd>
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| 108 | <dt>OV_EINVAL</dt>
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| 109 | <dd>indicates the initial file headers couldn't be read or
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| 110 | are corrupt, or that the initial open call for <i>vf</i>
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| 111 | failed.</dd>
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| 112 | <dt>0</dt>
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| 113 | <dd>indicates EOF</dd>
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| 114 | <dt><i>n</i></dt>
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| 115 | <dd>indicates actual number of bytes read. <tt>ov_read()</tt> will
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| 116 | decode at most one vorbis packet per invocation, so the value
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| 117 | returned will generally be less than <tt>length</tt>.
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| 118 | </dl>
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| 119 | </blockquote>
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| 120 |
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| 121 | <h3>Notes</h3>
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| 122 | <p><b>Typical usage:</b>
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| 123 | <blockquote>
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| 124 | <tt>bytes_read = ov_read(&vf,
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| 125 | buffer, 4096,0,2,1,&current_section)</tt>
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| 126 | </blockquote>
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| 127 |
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| 128 | This reads up to 4096 bytes into a buffer, with signed 16-bit
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| 129 | little-endian samples.
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| 130 | </p>
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| 131 |
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| 132 |
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| 133 |
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| 134 | <br><br>
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| 135 | <hr noshade>
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| 136 | <table border=0 width=100%>
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| 137 | <tr valign=top>
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| 138 | <td><p class=tiny>copyright © 2000-2010 Xiph.Org</p></td>
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| 139 | <td align=right><p class=tiny><a href="https://xiph.org/vorbis/">Ogg Vorbis</a></p></td>
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| 140 | </tr><tr>
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| 141 | <td><p class=tiny>Vorbisfile documentation</p></td>
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| 142 | <td align=right><p class=tiny>vorbisfile version 1.3.2 - 20101101</p></td>
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| 143 | </tr>
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| 144 | </table>
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| 145 |
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| 146 | </body>
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| 147 |
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| 148 | </html>
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