1<html> 2 3<head> 4<title>Tremor - function - ov_read</title> 5<link rel=stylesheet href="style.css" type="text/css"> 6</head> 7 8<body bgcolor=white text=black link="#5555ff" alink="#5555ff" vlink="#5555ff"> 9<table border=0 width=100%> 10<tr> 11<td><p class=tiny>Tremor documentation</p></td> 12<td align=right><p class=tiny>Tremor version 1.0 - 20020403</p></td> 13</tr> 14</table> 15 16<h1>ov_read()</h1> 17 18<p><i>declared in "ivorbisfile.h";</i></p> 19 20<p> 21 This is the main function used to decode a Vorbis file within a 22 loop. It returns up to the specified number of bytes of decoded audio 23 in host-endian, signed 16 bit PCM format. If the audio is 24 multichannel, the channels are interleaved in the output buffer. 25 If the passed in buffer is large, <tt>ov_read()</tt> will not fill 26 it; the passed in buffer size is treated as a <em>limit</em> and 27 not a request. 28<p> 29 30Note that up to this point, the Tremor API could more or less hide the 31 multiple logical bitstream nature of chaining from the toplevel 32 application if the toplevel application didn't particularly care. 33 However, when reading audio back, the application must be aware 34 that multiple bitstream sections do not necessarily use the same 35 number of channels or sampling rate. <p> <tt>ov_read()</tt> passes 36 back the index of the sequential logical bitstream currently being 37 decoded (in <tt>*bitstream</tt>) along with the PCM data in order 38 that the toplevel application can handle channel and/or sample 39 rate changes. This number will be incremented at chaining 40 boundaries even for non-seekable streams. For seekable streams, it 41 represents the actual chaining index within the physical bitstream. 42<p> 43 44<br><br> 45<table border=0 color=black cellspacing=0 cellpadding=7> 46<tr bgcolor=#cccccc> 47 <td> 48<pre><b> 49long ov_read(<a href="OggVorbis_File.html">OggVorbis_File</a> *vf, char *buffer, int length, int *bitstream); 50</b></pre> 51 </td> 52</tr> 53</table> 54 55<h3>Parameters</h3> 56<dl> 57<dt><i>vf</i></dt> 58<dd>A pointer to the OggVorbis_File structure--this is used for ALL the externally visible libvorbisidec 59functions.</dd> 60<dt><i>buffer</i></dt> 61<dd>A pointer to an output buffer. The decoded output is inserted into this buffer.</dd> 62<dt><i>length</i></dt> 63<dd>Number of bytes to be read into the buffer. Should be the same size as the buffer. A typical value is 4096.</dd> 64<dt><i>bitstream</i></dt> 65<dd>A pointer to the number of the current logical bitstream.</dd> 66</dl> 67 68 69<h3>Return Values</h3> 70<blockquote> 71<dl> 72<dt>OV_HOLE</dt> 73 <dd>indicates there was an interruption in the data. 74 <br>(one of: garbage between pages, loss of sync followed by 75 recapture, or a corrupt page)</dd> 76<dt>OV_EBADLINK</dt> 77 <dd>indicates that an invalid stream section was supplied to 78 libvorbisidec, or the requested link is corrupt.</dd> 79<dt>0</dt> 80 <dd>indicates EOF</dd> 81<dt><i>n</i></dt> 82 <dd>indicates actual number of bytes read. <tt>ov_read()</tt> will 83 decode at most one vorbis packet per invocation, so the value 84 returned will generally be less than <tt>length</tt>. 85</dl> 86</blockquote> 87 88<h3>Notes</h3> 89<p><b>Typical usage:</b> 90<blockquote> 91<tt>bytes_read = ov_read(&vf, 92buffer, 4096,&current_section)</tt> 93</blockquote> 94 95This reads up to 4096 bytes into a buffer, with signed 16-bit 96little-endian samples. 97</p> 98 99 100 101<br><br> 102<hr noshade> 103<table border=0 width=100%> 104<tr valign=top> 105<td><p class=tiny>copyright © 2002 Xiph.org</p></td> 106<td align=right><p class=tiny><a href="http://www.xiph.org/ogg/vorbis/">Ogg Vorbis</a></p></td> 107</tr><tr> 108<td><p class=tiny>Tremor documentation</p></td> 109<td align=right><p class=tiny>Tremor version 1.0 - 20020403</p></td> 110</tr> 111</table> 112 113</body> 114 115</html> 116