1<html> 2 3<head> 4<title>Tremor - function - ov_open</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_open</h1> 17 18<p><i>declared in "ivorbisfile.h";</i></p> 19 20<p>This is the main function used to open and initialize an OggVorbis_File 21structure. It sets up all the related decoding structure. 22<p>The first argument must be a file pointer to an already opened file 23or pipe (it need not be seekable--though this obviously restricts what 24can be done with the bitstream). <tt>vf</tt> should be a pointer to the 25OggVorbis_File structure--this is used for ALL the externally visible libvorbisidec 26functions. Once this has been called, the same <a href="OggVorbis_File.html">OggVorbis_File</a> 27struct should be passed to all the libvorbisidec functions. 28<p>Also, you should be aware that ov_open(), once successful, takes complete possession of the file resource. After you have opened a file using ov_open(), you MUST close it using <a href="ov_clear.html">ov_clear()</a>, not fclose() or any other function. 29<p> 30It is often useful to call <tt>ov_open()</tt> 31simply to determine whether a given file is a vorbis bitstream. If the 32<tt>ov_open()</tt> 33call fails, then the file is not recognizable as such. 34When you use <tt>ov_open() 35</tt>for 36this, you should <tt>fclose()</tt> the file pointer if, and only if, the 37<tt>ov_open()</tt> 38call fails. If it succeeds, you must call <a href="ov_clear.html">ov_clear()</a> to clear 39the decoder's buffers and close the file for you.<p> 40 41(Note that <a href="ov_test.html">ov_test()</a> provides a less expensive way to test a file for Vorbisness.)<p> 42 43<br><br> 44<table border=0 color=black cellspacing=0 cellpadding=7> 45<tr bgcolor=#cccccc> 46 <td> 47<pre><b> 48int ov_open(FILE *f,<a href="OggVorbis_File.html">OggVorbis_File</a> *vf,char *initial,long ibytes); 49</b></pre> 50 </td> 51</tr> 52</table> 53 54<h3>Parameters</h3> 55<dl> 56<dt><i>f</i></dt> 57<dd>File pointer to an already opened file 58or pipe (it need not be seekable--though this obviously restricts what 59can be done with the bitstream).</dd> 60<dt><i>vf</i></dt> 61<dd>A pointer to the OggVorbis_File structure--this is used for ALL the externally visible libvorbisidec 62functions. Once this has been called, the same <tt>OggVorbis_File</tt> 63struct should be passed to all the libvorbisidec functions.</dd> 64<dt><i>initial</i></dt> 65<dd>Typically set to NULL. This parameter is useful if some data has already been 66read from the file and the stream is not seekable. It is used in conjunction with <tt>ibytes</tt>. In this case, <tt>initial</tt> 67should be a pointer to a buffer containing the data read.</dd> 68<dt><i>ibytes</i></dt> 69<dd>Typically set to 0. This parameter is useful if some data has already been 70read from the file and the stream is not seekable. In this case, <tt>ibytes</tt> 71should contain the length (in bytes) of the buffer. Used together with <tt>initial</tt></dd> 72</dl> 73 74 75<h3>Return Values</h3> 76<blockquote> 77<li>0 indicates success</li> 78 79<li>less than zero for failure:</li> 80<ul> 81<li>OV_EREAD - A read from media returned an error.</li> 82<li>OV_ENOTVORBIS - Bitstream is not Vorbis data.</li> 83<li>OV_EVERSION - Vorbis version mismatch.</li> 84<li>OV_EBADHEADER - Invalid Vorbis bitstream header.</li> 85<li>OV_EFAULT - Internal logic fault; indicates a bug or heap/stack corruption.</li> 86</ul> 87</blockquote> 88<p> 89 90<h3>Notes</h3> 91<p>If your decoder is threaded, it is recommended that you NOT call 92<tt>ov_open()</tt> 93in the main control thread--instead, call <tt>ov_open()</tt> IN your decode/playback 94thread. This is important because <tt>ov_open()</tt> may be a fairly time-consuming 95call, given that the full structure of the file is determined at this point, 96which may require reading large parts of the file under certain circumstances 97(determining all the logical bitstreams in one physical bitstream, for 98example). See <a href="threads.html">Thread Safety</a> for other information on using libvorbisidec with threads. 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