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115 lines
4.5 KiB
115 lines
4.5 KiB
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<title>Tremor - function - ov_open</title>
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<link rel=stylesheet href="style.css" type="text/css">
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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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<td><p class=tiny>Tremor documentation</p></td>
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<td align=right><p class=tiny>Tremor version 1.0 - 20020403</p></td>
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<h1>ov_open</h1>
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<p><i>declared in "ivorbisfile.h";</i></p>
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<p>This is the main function used to open and initialize an OggVorbis_File
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structure. It sets up all the related decoding structure.
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<p>The first argument must be a file pointer to an already opened file
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or pipe (it need not be seekable--though this obviously restricts what
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can be done with the bitstream). <tt>vf</tt> should be a pointer to the
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OggVorbis_File structure--this is used for ALL the externally visible libvorbisidec
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functions. Once this has been called, the same <a href="OggVorbis_File.html">OggVorbis_File</a>
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struct should be passed to all the libvorbisidec functions.
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<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.
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<p>
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It is often useful to call <tt>ov_open()</tt>
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simply to determine whether a given file is a vorbis bitstream. If the
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<tt>ov_open()</tt>
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call fails, then the file is not recognizable as such.
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When you use <tt>ov_open()
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</tt>for
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this, you should <tt>fclose()</tt> the file pointer if, and only if, the
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<tt>ov_open()</tt>
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call fails. If it succeeds, you must call <a href="ov_clear.html">ov_clear()</a> to clear
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the decoder's buffers and close the file for you.<p>
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(Note that <a href="ov_test.html">ov_test()</a> provides a less expensive way to test a file for Vorbisness.)<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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int ov_open(FILE *f,<a href="OggVorbis_File.html">OggVorbis_File</a> *vf,char *initial,long ibytes);
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</b></pre>
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</td>
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</table>
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<h3>Parameters</h3>
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<dl>
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<dt><i>f</i></dt>
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<dd>File pointer to an already opened file
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or pipe (it need not be seekable--though this obviously restricts what
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can be done with the bitstream).</dd>
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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 libvorbisidec
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functions. Once this has been called, the same <tt>OggVorbis_File</tt>
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struct should be passed to all the libvorbisidec functions.</dd>
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<dt><i>initial</i></dt>
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<dd>Typically set to NULL. This parameter is useful if some data has already been
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read from the file and the stream is not seekable. It is used in conjunction with <tt>ibytes</tt>. In this case, <tt>initial</tt>
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should be a pointer to a buffer containing the data read.</dd>
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<dt><i>ibytes</i></dt>
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<dd>Typically set to 0. This parameter is useful if some data has already been
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read from the file and the stream is not seekable. In this case, <tt>ibytes</tt>
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should contain the length (in bytes) of the buffer. Used together with <tt>initial</tt></dd>
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</dl>
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<h3>Return Values</h3>
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<blockquote>
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<li>0 indicates success</li>
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<li>less than zero for failure:</li>
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<ul>
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<li>OV_EREAD - A read from media returned an error.</li>
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<li>OV_ENOTVORBIS - Bitstream is not Vorbis data.</li>
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<li>OV_EVERSION - Vorbis version mismatch.</li>
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<li>OV_EBADHEADER - Invalid Vorbis bitstream header.</li>
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<li>OV_EFAULT - Internal logic fault; indicates a bug or heap/stack corruption.</li>
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</ul>
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</blockquote>
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<p>
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<h3>Notes</h3>
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<p>If your decoder is threaded, it is recommended that you NOT call
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<tt>ov_open()</tt>
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in the main control thread--instead, call <tt>ov_open()</tt> IN your decode/playback
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thread. This is important because <tt>ov_open()</tt> may be a fairly time-consuming
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call, given that the full structure of the file is determined at this point,
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which may require reading large parts of the file under certain circumstances
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(determining all the logical bitstreams in one physical bitstream, for
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example). See <a href="threads.html">Thread Safety</a> for other information on using libvorbisidec with threads.
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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 © 2002 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>Tremor documentation</p></td>
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<td align=right><p class=tiny>Tremor version 1.0 - 20020403</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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