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| <title>Vorbisfile - function - ov_read</title> |
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| <td><p class=tiny>Vorbisfile documentation</p></td> |
| <td align=right><p class=tiny>vorbisfile version 1.2.0 - 20070723</p></td> |
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| </table> |
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| <h1>ov_read()</h1> |
| |
| <p><i>declared in "vorbis/vorbisfile.h";</i></p> |
| |
| <p> |
| This is the main function used to decode a Vorbis file within a |
| loop. It returns up to the specified number of bytes of decoded PCM audio |
| in the requested endianness, signedness, and word size. If the audio is |
| multichannel, the channels are interleaved in the output buffer. |
| If the passed in buffer is large, <tt>ov_read()</tt> will not fill |
| it; the passed in buffer size is treated as a <em>limit</em> and |
| not a request. |
| |
| <p>The output channels are in stream order and not remapped. Vorbis I |
| defines channel order as follows: |
| |
| <ul> |
| <li>one channel - the stream is monophonic |
| <li>two channels - the stream is stereo. channel order: left, right |
| <li>three channels - the stream is a 1d-surround encoding. channel order: left, |
| center, right |
| <li>four channels - the stream is quadraphonic surround. channel order: front left, |
| front right, rear left, rear right |
| <li>five channels - the stream is five-channel surround. channel order: front left, |
| center, front right, rear left, rear right |
| <li>six channels - the stream is 5.1 surround. channel order: front left, center, |
| front right, rear left, rear right, LFE |
| <li>seven channels - the stream is 6.1 surround. channel order: front left, center, |
| front right, side left, side right, rear center, LFE |
| <li>eight channels - the stream is 7.1 surround. channel order: front left, center, |
| front right, side left, side right, rear left, rear right, |
| LFE |
| <li>greater than eight channels - channel use and order is undefined |
| </ul> |
| |
| <p>Note that up to this point, the Vorbisfile API could more or less hide the |
| multiple logical bitstream nature of chaining from the toplevel |
| application if the toplevel application didn't particularly care. |
| However, when reading audio back, the application must be aware |
| that multiple bitstream sections do not necessarily use the same |
| number of channels or sampling rate. <p> <tt>ov_read()</tt> passes |
| back the index of the sequential logical bitstream currently being |
| decoded (in <tt>*bitstream</tt>) along with the PCM data in order |
| that the toplevel application can handle channel and/or sample |
| rate changes. This number will be incremented at chaining |
| boundaries even for non-seekable streams. For seekable streams, it |
| represents the actual chaining index within the physical bitstream. |
| <p> |
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| <br><br> |
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| <pre><b> |
| long ov_read(<a href="OggVorbis_File.html">OggVorbis_File</a> *vf, char *buffer, int length, int bigendianp, int word, int sgned, int *bitstream); |
| </b></pre> |
| </td> |
| </tr> |
| </table> |
| |
| <h3>Parameters</h3> |
| <dl> |
| <dt><i>vf</i></dt> |
| <dd>A pointer to the OggVorbis_File structure--this is used for ALL the externally visible libvorbisfile |
| functions.</dd> |
| <dt><i>buffer</i></dt> |
| <dd>A pointer to an output buffer. The decoded output is inserted into this buffer.</dd> |
| <dt><i>length</i></dt> |
| <dd>Number of bytes to be read into the buffer. Should be the same size as the buffer. A typical value is 4096.</dd> |
| <dt><i>bigendianp</i></dt> |
| <dd>Specifies big or little endian byte packing. 0 for little endian, 1 for b |
| ig endian. Typical value is 0.</dd> |
| <dt><i>word</i></dt> |
| <dd>Specifies word size. Possible arguments are 1 for 8-bit samples, or 2 or |
| 16-bit samples. Typical value is 2.</dd> |
| <dt><i>sgned</i></dt> |
| <dd>Signed or unsigned data. 0 for unsigned, 1 for signed. Typically 1.</dd> |
| <dt><i>bitstream</i></dt> |
| <dd>A pointer to the number of the current logical bitstream.</dd> |
| </dl> |
| |
| |
| <h3>Return Values</h3> |
| <blockquote> |
| <dl> |
| <dt>OV_HOLE</dt> |
| <dd>indicates there was an interruption in the data. |
| <br>(one of: garbage between pages, loss of sync followed by |
| recapture, or a corrupt page)</dd> |
| <dt>OV_EBADLINK</dt> |
| <dd>indicates that an invalid stream section was supplied to |
| libvorbisfile, or the requested link is corrupt.</dd> |
| <dt>OV_EINVAL</dt> |
| <dd>indicates the initial file headers couldn't be read or |
| are corrupt, or that the initial open call for <i>vf</i> |
| failed.</dd> |
| <dt>0</dt> |
| <dd>indicates EOF</dd> |
| <dt><i>n</i></dt> |
| <dd>indicates actual number of bytes read. <tt>ov_read()</tt> will |
| decode at most one vorbis packet per invocation, so the value |
| returned will generally be less than <tt>length</tt>. |
| </dl> |
| </blockquote> |
| |
| <h3>Notes</h3> |
| <p><b>Typical usage:</b> |
| <blockquote> |
| <tt>bytes_read = ov_read(&vf, |
| buffer, 4096,0,2,1,&current_section)</tt> |
| </blockquote> |
| |
| This reads up to 4096 bytes into a buffer, with signed 16-bit |
| little-endian samples. |
| </p> |
| |
| |
| |
| <br><br> |
| <hr noshade> |
| <table border=0 width=100%> |
| <tr valign=top> |
| <td><p class=tiny>copyright © 2007 Xiph.org</p></td> |
| <td align=right><p class=tiny><a href="http://www.xiph.org/ogg/vorbis/">Ogg Vorbis</a></p></td> |
| </tr><tr> |
| <td><p class=tiny>Vorbisfile documentation</p></td> |
| <td align=right><p class=tiny>vorbisfile version 1.2.0 - 20070723</p></td> |
| </tr> |
| </table> |
| |
| </body> |
| |
| </html> |