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00004 <title>Tremor - function - ov_read</title>
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00008 <body bgcolor=white text=black link="#5555ff" alink="#5555ff" vlink="#5555ff">
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00011 <td><p class=tiny>Tremor documentation</p></td>
00012 <td align=right><p class=tiny>Tremor version 1.0 - 20020403</p></td>
00013 </tr>
00014 </table>
00015
00016 <h1>ov_read()</h1>
00017
00018 <p><i>declared in "ivorbisfile.h";</i></p>
00019
00020 <p>
00021 This is the main function used to decode a Vorbis file within a
00022 loop. It returns up to the specified number of bytes of decoded audio
00023 in host-endian, signed 16 bit PCM format. If the audio is
00024 multichannel, the channels are interleaved in the output buffer.
00025 If the passed in buffer is large, <tt>ov_read()</tt> will not fill
00026 it; the passed in buffer size is treated as a <em>limit</em> and
00027 not a request.
00028 <p>
00029
00030 Note that up to this point, the Tremor API could more or less hide the
00031 multiple logical bitstream nature of chaining from the toplevel
00032 application if the toplevel application didn't particularly care.
00033 However, when reading audio back, the application must be aware
00034 that multiple bitstream sections do not necessarily use the same
00035 number of channels or sampling rate. <p> <tt>ov_read()</tt> passes
00036 back the index of the sequential logical bitstream currently being
00037 decoded (in <tt>*bitstream</tt>) along with the PCM data in order
00038 that the toplevel application can handle channel and/or sample
00039 rate changes. This number will be incremented at chaining
00040 boundaries even for non-seekable streams. For seekable streams, it
00041 represents the actual chaining index within the physical bitstream.
00042 <p>
00043
00044 <br><br>
00045 <table border=0 color=black cellspacing=0 cellpadding=7>
00046 <tr bgcolor=#cccccc>
00047 <td>
00048 <pre><b>
00049 long ov_read(<a href="OggVorbis_File.html">OggVorbis_File</a> *vf, char *buffer, int length, int *bitstream);
00050 </b></pre>
00051 </td>
00052 </tr>
00053 </table>
00054
00055 <h3>Parameters</h3>
00056 <dl>
00057 <dt><i>vf</i></dt>
00058 <dd>A pointer to the OggVorbis_File structure--this is used for ALL the externally visible libvorbisidec
00059 functions.</dd>
00060 <dt><i>buffer</i></dt>
00061 <dd>A pointer to an output buffer. The decoded output is inserted into this buffer.</dd>
00062 <dt><i>length</i></dt>
00063 <dd>Number of bytes to be read into the buffer. Should be the same size as the buffer. A typical value is 4096.</dd>
00064 <dt><i>bitstream</i></dt>
00065 <dd>A pointer to the number of the current logical bitstream.</dd>
00066 </dl>
00067
00068
00069 <h3>Return Values</h3>
00070 <blockquote>
00071 <dl>
00072 <dt>OV_HOLE</dt>
00073 <dd>indicates there was an interruption in the data.
00074 <br>(one of: garbage between pages, loss of sync followed by
00075 recapture, or a corrupt page)</dd>
00076 <dt>OV_EBADLINK</dt>
00077 <dd>indicates that an invalid stream section was supplied to
00078 libvorbisidec, or the requested link is corrupt.</dd>
00079 <dt>0</dt>
00080 <dd>indicates EOF</dd>
00081 <dt><i>n</i></dt>
00082 <dd>indicates actual number of bytes read. <tt>ov_read()</tt> will
00083 decode at most one vorbis packet per invocation, so the value
00084 returned will generally be less than <tt>length</tt>.
00085 </dl>
00086 </blockquote>
00087
00088 <h3>Notes</h3>
00089 <p><b>Typical usage:</b>
00090 <blockquote>
00091 <tt>bytes_read = ov_read(&vf,
00092 buffer, 4096,&current_section)</tt>
00093 </blockquote>
00094
00095 This reads up to 4096 bytes into a buffer, with signed 16-bit
00096 little-endian samples.
00097 </p>
00098
00099
00100
00101 <br><br>
00102 <hr noshade>
00103 <table border=0 width=100%>
00104 <tr valign=top>
00105 <td><p class=tiny>copyright © 2002 Xiph.org</p></td>
00106 <td align=right><p class=tiny><a href="http://www.xiph.org/ogg/vorbis/">Ogg Vorbis</a></p></td>
00107 </tr><tr>
00108 <td><p class=tiny>Tremor documentation</p></td>
00109 <td align=right><p class=tiny>Tremor version 1.0 - 20020403</p></td>
00110 </tr>
00111 </table>
00112
00113 </body>
00114
00115 </html>
