149 lines
5.3 KiB
HTML
149 lines
5.3 KiB
HTML
<html>
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<head>
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<title>Vorbisfile - function - ov_read</title>
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<link rel=stylesheet href="style.css" type="text/css">
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</head>
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<body bgcolor=white text=black link="#5555ff" alink="#5555ff" vlink="#5555ff">
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<table border=0 width=100%>
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<tr>
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<td><p class=tiny>Vorbisfile documentation</p></td>
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<td align=right><p class=tiny>vorbisfile version 1.3.2 - 20101101</p></td>
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</tr>
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</table>
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<h1>ov_read()</h1>
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<p><i>declared in "vorbis/vorbisfile.h";</i></p>
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<p>
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This is the main function used to decode a Vorbis file within a
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loop. It returns up to the specified number of bytes of decoded PCM audio
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in the requested endianness, signedness, and word size. If the audio is
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multichannel, the channels are interleaved in the output buffer.
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If the passed in buffer is large, <tt>ov_read()</tt> will not fill
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it; the passed in buffer size is treated as a <em>limit</em> and
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not a request.
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<p>The output channels are in stream order and not remapped. Vorbis I
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defines channel order as follows:
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<ul>
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<li>one channel - the stream is monophonic
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<li>two channels - the stream is stereo. channel order: left, right
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<li>three channels - the stream is a 1d-surround encoding. channel order: left,
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center, right
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<li>four channels - the stream is quadraphonic surround. channel order: front left,
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front right, rear left, rear right
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<li>five channels - the stream is five-channel surround. channel order: front left,
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center, front right, rear left, rear right
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<li>six channels - the stream is 5.1 surround. channel order: front left, center,
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front right, rear left, rear right, LFE
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<li>seven channels - the stream is 6.1 surround. channel order: front left, center,
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front right, side left, side right, rear center, LFE
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<li>eight channels - the stream is 7.1 surround. channel order: front left, center,
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front right, side left, side right, rear left, rear right,
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LFE
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<li>greater than eight channels - channel use and order is undefined
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</ul>
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<p>Note that up to this point, the Vorbisfile API could more or less hide the
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multiple logical bitstream nature of chaining from the toplevel
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application if the toplevel application didn't particularly care.
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However, when reading audio back, the application must be aware
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that multiple bitstream sections do not necessarily use the same
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number of channels or sampling rate. <p> <tt>ov_read()</tt> passes
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back the index of the sequential logical bitstream currently being
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decoded (in <tt>*bitstream</tt>) along with the PCM data in order
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that the toplevel application can handle channel and/or sample
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rate changes. This number will be incremented at chaining
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boundaries even for non-seekable streams. For seekable streams, it
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represents the actual chaining index within the physical bitstream.
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<p>
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<br><br>
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<table border=0 color=black cellspacing=0 cellpadding=7>
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<tr bgcolor=#cccccc>
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<td>
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<pre><b>
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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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</b></pre>
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</td>
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</tr>
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</table>
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<h3>Parameters</h3>
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<dl>
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<dt><i>vf</i></dt>
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<dd>A pointer to the OggVorbis_File structure--this is used for ALL the externally visible libvorbisfile
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functions.</dd>
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<dt><i>buffer</i></dt>
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<dd>A pointer to an output buffer. The decoded output is inserted into this buffer.</dd>
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<dt><i>length</i></dt>
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<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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<dt><i>bigendianp</i></dt>
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<dd>Specifies big or little endian byte packing. 0 for little endian, 1 for b
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ig endian. Typical value is 0.</dd>
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<dt><i>word</i></dt>
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<dd>Specifies word size. Possible arguments are 1 for 8-bit samples, or 2 or
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16-bit samples. Typical value is 2.</dd>
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<dt><i>sgned</i></dt>
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<dd>Signed or unsigned data. 0 for unsigned, 1 for signed. Typically 1.</dd>
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<dt><i>bitstream</i></dt>
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<dd>A pointer to the number of the current logical bitstream.</dd>
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</dl>
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<h3>Return Values</h3>
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<blockquote>
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<dl>
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<dt>OV_HOLE</dt>
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<dd>indicates there was an interruption in the data.
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<br>(one of: garbage between pages, loss of sync followed by
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recapture, or a corrupt page)</dd>
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<dt>OV_EBADLINK</dt>
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<dd>indicates that an invalid stream section was supplied to
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libvorbisfile, or the requested link is corrupt.</dd>
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<dt>OV_EINVAL</dt>
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<dd>indicates the initial file headers couldn't be read or
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are corrupt, or that the initial open call for <i>vf</i>
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failed.</dd>
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<dt>0</dt>
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<dd>indicates EOF</dd>
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<dt><i>n</i></dt>
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<dd>indicates actual number of bytes read. <tt>ov_read()</tt> will
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decode at most one vorbis packet per invocation, so the value
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returned will generally be less than <tt>length</tt>.
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</dl>
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</blockquote>
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<h3>Notes</h3>
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<p><b>Typical usage:</b>
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<blockquote>
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<tt>bytes_read = ov_read(&vf,
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buffer, 4096,0,2,1,&current_section)</tt>
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</blockquote>
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This reads up to 4096 bytes into a buffer, with signed 16-bit
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little-endian samples.
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</p>
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<br><br>
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<hr noshade>
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<table border=0 width=100%>
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<tr valign=top>
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<td><p class=tiny>copyright © 2000-2010 Xiph.Org</p></td>
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<td align=right><p class=tiny><a href="http://www.xiph.org/ogg/vorbis/">Ogg Vorbis</a></p></td>
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</tr><tr>
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<td><p class=tiny>Vorbisfile documentation</p></td>
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<td align=right><p class=tiny>vorbisfile version 1.3.2 - 20101101</p></td>
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</tr>
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</table>
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</body>
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</html>
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