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- <title>Vorbisfile - function - ov_open_callbacks</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>
- </tr>
- </table>
- <h1>ov_open_callbacks</h1>
- <p><i>declared in "vorbis/vorbisfile.h";</i></p>
- <p>This is an alternative function used to open and initialize an
- OggVorbis_File structure when using a data source other than a file,
- when its necessary to modify default file access behavior, or to
- initialize a Vorbis decode from a <tt>FILE *</tt> pointer under
- Windows where <a href="ov_open.html">ov_open()</a> cannot be used. It
- allows the application to specify custom file manipulation routines
- and sets up all the related decoding structures.
- <p>Once ov_open_callbacks() has been called, the same
- <tt>OggVorbis_File</tt> struct should be passed to all the
- libvorbisfile functions. Unlike <a
- href="ov_fopen.html">ov_fopen()</a> and <a
- href="ov_open.html">ov_open()</a>, ov_open_callbacks() may be used to
- instruct vorbisfile to either automatically close or not to close the
- file/data access handle in <a href="ov_clear.html">ov_clear()</a>.
- Automatic closure is disabled by passing NULL as the close callback,
- or using one of the predefined callback sets that specify a NULL close
- callback. The application is responsible for closing a file when a
- call to ov_open_callbacks() is unsuccessful.<p>
- See also <a href="callbacks.html">Callbacks and Non-stdio I/O</a> for
- information on designing and specifying custom callback functions.<p>
- <br><br>
- <table border=0 color=black cellspacing=0 cellpadding=7>
- <tr bgcolor=#cccccc>
- <td>
- <pre><b>
- int ov_open_callbacks(void *datasource, <a href="OggVorbis_File.html">OggVorbis_File</a> *vf, char *initial, long ibytes, <a href="ov_callbacks.html">ov_callbacks</a> callbacks);
- </b></pre>
- </td>
- </tr>
- </table>
- <h3>Parameters</h3>
- <dl>
- <dt><i>datasource</i></dt>
- <dd>Pointer to a data structure allocated by the calling application, containing any state needed by the callbacks provided.</dd>
- <dt><i>vf</i></dt>
- <dd>A pointer to the OggVorbis_File structure--this is used for ALL the externally visible libvorbisfile
- functions. Once this has been called, the same <tt>OggVorbis_File</tt>
- struct should be passed to all the libvorbisfile functions.</dd>
- <dt><i>initial</i></dt>
- <dd>Typically set to NULL. This parameter is useful if some data has already been
- read from the stream and the stream is not seekable. It is used in conjunction with <tt>ibytes</tt>. In this case, <tt>initial</tt>
- should be a pointer to a buffer containing the data read.</dd>
- <dt><i>ibytes</i></dt>
- <dd>Typically set to 0. This parameter is useful if some data has already been
- read from the stream and the stream is not seekable. In this case, <tt>ibytes</tt>
- should contain the length (in bytes) of the buffer. Used together with <tt>initial</tt>.</dd>
- <dt><i>callbacks</i></dt>
- <dd>A completed <a href="ov_callbacks.html">ov_callbacks</a> struct which indicates desired custom file manipulation routines. vorbisfile.h defines several preprovided callback sets; see <a href="ov_callbacks.html">ov_callbacks</a> for details.</dd>
- </dl>
- <h3>Return Values</h3>
- <blockquote>
- <li>0 for success</li>
- <li>less than zero for failure:</li>
- <ul>
- <li>OV_EREAD - A read from media returned an error.</li>
- <li>OV_ENOTVORBIS - Bitstream does not contain any Vorbis data.</li>
- <li>OV_EVERSION - Vorbis version mismatch.</li>
- <li>OV_EBADHEADER - Invalid Vorbis bitstream header.</li>
- <li>OV_EFAULT - Internal logic fault; indicates a bug or heap/stack corruption.</li>
- </ul>
- </blockquote>
- <p>
- <h3>Notes</h3>
- <dl>
- <dt><b>[a] Windows and use as an ov_open() substitute</b><p> Windows
- applications should not use <a href="ov_open.html">ov_open()</a> due
- to the likelihood of <a href="ov_open.html#winfoot">CRT linking
- mismatches and runtime protection faults
- [ov_open:a]</a>. ov_open_callbacks() is a safe substitute; specifically:
- <pre><tt>ov_open_callbacks(f, vf, initial, ibytes, OV_CALLBACKS_DEFAULT);</tt>
- </pre>
- ... provides exactly the same functionality as <a
- href="ov_open.html">ov_open()</a> but will always work correctly under
- Windows, regardless of linking setup details.<p>
- <dt><b>[b] Threaded decode</b><p>
- <dd>If your decoder is threaded, it is recommended that you NOT call
- <tt>ov_open_callbacks()</tt>
- in the main control thread--instead, call <tt>ov_open_callbacks()</tt> in your decode/playback
- thread. This is important because <tt>ov_open_callbacks()</tt> may be a fairly time-consuming
- call, given that the full structure of the file is determined at this point,
- which may require reading large parts of the file under certain circumstances
- (determining all the logical bitstreams in one physical bitstream, for
- example). See <a href="threads.html">Thread Safety</a> for other information on using libvorbisfile with threads.
- <p>
- <dt><b>[c] Mixed media streams</b><p>
- <dd>
- As of Vorbisfile release 1.2.0, Vorbisfile is able to access the
- Vorbis content in mixed-media Ogg streams, not just Vorbis-only
- streams. For example, Vorbisfile may be used to open and access the
- audio from an Ogg stream consisting of Theora video and Vorbis audio.
- Vorbisfile 1.2.0 decodes the first logical audio stream of each
- physical stream section.<p>
- <dt><b>[d] Faster testing for Vorbis files</b><p>
- <dd><a href="ov_test.html">ov_test()</a> and <a
- href="ov_test_callbacks.html">ov_test_callbacks()</a> provide less
- computationally expensive ways to test a file for Vorbisness, but
- require more setup code.<p>
- </dl>
- <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>
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