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 <head>
 <title>Vorbisfile - function - ov_open</title>
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 </head>

 <body bgcolor=white text=black link="#5555ff" alink="#5555ff" vlink="#5555ff">
 <table border=0 width=100%>
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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</h1>

 <p><i>declared in "vorbis/vorbisfile.h";</i></p>

 <p>ov_open is one of three initialization functions used to initialize
 an OggVorbis_File structure and prepare a bitstream for playback.

 <p><em><b> WARNING for Windows developers: </b> Do not use ov_open() in
 Windows applications; Windows linking places restrictions on
 passing <tt>FILE *</tt> handles successfully, and ov_open() runs
 afoul of these restrictions <a href="#winfoot">[a]</a>.  See the <a
 href="ov_open_callbacks.html">ov_open_callbacks() page </a> for
 details on using <a
 href="ov_open_callbacks.html">ov_open_callbacks()</a> instead. </em>

 <p>The first argument must be a file pointer to an already opened file
 or pipe (it need not be seekable--though this obviously restricts what
 can be done with the bitstream). <tt>vf</tt> should be a pointer to the
 OggVorbis_File structure -- this is used for ALL the externally visible libvorbisfile
 functions. Once this has been called, the same <a href="OggVorbis_File.html">OggVorbis_File</a>
 struct should be passed to all the libvorbisfile functions.<p>

 The <tt>vf</tt> structure initialized using ov_fopen() must eventually
 be cleaned using <a href="ov_clear.html">ov_clear()</a>.  Once a
 <tt>FILE *</tt> handle is passed to ov_open() successfully, the
 application MUST NOT <tt>fclose()</tt> or in any other way manipulate
 that file handle.  Vorbisfile will close the file in <a
 href="ov_clear.html">ov_clear()</a>.  If the application must be able
 to close the <tt>FILE *</tt> handle itself, see <a
 href="ov_open_callbacks.html">ov_open_callbacks()</a> with the use of
 <tt>OV_CALLBACKS_NOCLOSE</tt>.

 <p>It is often useful to call <tt>ov_open()</tt> simply to determine
 whether a given file is a Vorbis bitstream. If the <tt>ov_open()</tt>
 call fails, then the file is not recognizable as Vorbis.  If the call
 succeeds but the initialized <tt>vf</tt> structure will not be used,
 the application is responsible for calling <a
 href="ov_clear.html">ov_clear()</a> to clear the decoder's buffers and
 close the file.<p>

 If [and only if] an <tt>ov_open()</tt> call fails, the application
 must explicitly <tt>fclose()</tt> the <tt>FILE *</tt> pointer itself.


 <br><br>
 <table border=0 color=black cellspacing=0 cellpadding=7>
 <tr bgcolor=#cccccc>
 	<td>
 <pre><b>
 int ov_open(FILE *f,<a href="OggVorbis_File.html">OggVorbis_File</a> *vf,char *initial,long ibytes);
 </b></pre>
 	</td>
 </tr>
 </table>

 <h3>Parameters</h3>
 <dl>
 <dt><i>f</i></dt>
 <dd>File pointer to an already opened file
 or pipe (it need not be seekable--though this obviously restricts what
 can be done with the bitstream).</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 file 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 file 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>
 </dl>


 <h3>Return Values</h3>
 <blockquote>
 <li>0 indicates 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 is not 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>

 <a name="notes"></a>
 <h3>Notes</h3>
 <dl>

 <a name="winfoot"></a>
 <dt><b>[a] Windows and ov_open()</b><p>

 <dd>Under Windows, stdio file access is implemented in each of many
 variants of crt.o, several of which are typically installed on any one
 Windows machine.  If libvorbisfile and the application using
 libvorbisfile are not linked against the exact same
 version/variant/build of crt.o (and they usually won't be, especially
 using a prebuilt libvorbis DLL), <tt>FILE *</tt> handles cannot be
 opened in the application and then passed to vorbisfile to be used
 by stdio calls from vorbisfile's different version of CRT.  For this
 reason, using <a href="ov_open.html">ov_open()</a> under Windows
 without careful, expert linking will typically cause a protection
 fault.  Windows programmers should use <a
 href="ov_fopen.html">ov_fopen()</a> (which will only use libvorbis's
 crt.o) or <a href="ov_open_callbacks.html">ov_open_callbacks()</a>
 (which will only use the application's crt.o) instead.<p>

 This warning only applies to Windows and only applies to <a
 href="ov_open.html">ov_open()</a>.  It is perfectly safe to use <a
 href="ov_open.html">ov_open()</a> on all other platforms.<p>

 For more information, see the following microsoft pages on <a
 href="http://msdn2.microsoft.com/en-us/library/abx4dbyh(VS.80).aspx">C
 runtime library linking</a> and a specific description of <a
 href="http://msdn2.microsoft.com/en-us/library/ms235460(VS.80).aspx">restrictions
 on passing CRT objects across DLL boundaries</a>.

 <p>

 <dt><b>[b] Threaded decode</b><p>
 <dd>If your decoder is threaded, it is recommended that you NOT call
 <tt>ov_open()</tt>
 in the main control thread--instead, call <tt>ov_open()</tt> in your decode/playback
 thread. This is important because <tt>ov_open()</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 &copy; 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>
	<html>

	<head>
	<title>Vorbisfile - function - ov_open</title>
	<link rel=stylesheet href="style.css" type="text/css">
	</head>

	<body bgcolor=white text=black link="#5555ff" alink="#5555ff" vlink="#5555ff">
	<table border=0 width=100%>
	<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>

	<h1>ov_open</h1>

	<p><i>declared in "vorbis/vorbisfile.h";</i></p>

	<p>ov_open is one of three initialization functions used to initialize
	an OggVorbis_File structure and prepare a bitstream for playback.

	<p><em><b> WARNING for Windows developers: </b> Do not use ov_open() in
	Windows applications; Windows linking places restrictions on
	passing <tt>FILE *</tt> handles successfully, and ov_open() runs
	afoul of these restrictions <a href="#winfoot">[a]</a>. See the <a
	href="ov_open_callbacks.html">ov_open_callbacks() page </a> for
	details on using <a
	href="ov_open_callbacks.html">ov_open_callbacks()</a> instead. </em>

	<p>The first argument must be a file pointer to an already opened file
	or pipe (it need not be seekable--though this obviously restricts what
	can be done with the bitstream). <tt>vf</tt> should be a pointer to the
	OggVorbis_File structure -- this is used for ALL the externally visible libvorbisfile
	functions. Once this has been called, the same <a href="OggVorbis_File.html">OggVorbis_File</a>
	struct should be passed to all the libvorbisfile functions.<p>

	The <tt>vf</tt> structure initialized using ov_fopen() must eventually
	be cleaned using <a href="ov_clear.html">ov_clear()</a>. Once a
	<tt>FILE *</tt> handle is passed to ov_open() successfully, the
	application MUST NOT <tt>fclose()</tt> or in any other way manipulate
	that file handle. Vorbisfile will close the file in <a
	href="ov_clear.html">ov_clear()</a>. If the application must be able
	to close the <tt>FILE *</tt> handle itself, see <a
	href="ov_open_callbacks.html">ov_open_callbacks()</a> with the use of
	<tt>OV_CALLBACKS_NOCLOSE</tt>.

	<p>It is often useful to call <tt>ov_open()</tt> simply to determine
	whether a given file is a Vorbis bitstream. If the <tt>ov_open()</tt>
	call fails, then the file is not recognizable as Vorbis. If the call
	succeeds but the initialized <tt>vf</tt> structure will not be used,
	the application is responsible for calling <a
	href="ov_clear.html">ov_clear()</a> to clear the decoder's buffers and
	close the file.<p>

	If [and only if] an <tt>ov_open()</tt> call fails, the application
	must explicitly <tt>fclose()</tt> the <tt>FILE *</tt> pointer itself.


	<br><br>
	<table border=0 color=black cellspacing=0 cellpadding=7>
	<tr bgcolor=#cccccc>
	<td>
	<pre><b>
	int ov_open(FILE f,<a href="OggVorbis_File.html">OggVorbis_File</a> vf,char *initial,long ibytes);
	</b></pre>
	</td>
	</tr>
	</table>

	<h3>Parameters</h3>
	<dl>
	<dt><i>f</i></dt>
	<dd>File pointer to an already opened file
	or pipe (it need not be seekable--though this obviously restricts what
	can be done with the bitstream).</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 file 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 file 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>
	</dl>


	<h3>Return Values</h3>
	<blockquote>
	<li>0 indicates 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 is not 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>

	<a name="notes"></a>
	<h3>Notes</h3>
	<dl>

	<a name="winfoot"></a>
	<dt><b>[a] Windows and ov_open()</b><p>

	<dd>Under Windows, stdio file access is implemented in each of many
	variants of crt.o, several of which are typically installed on any one
	Windows machine. If libvorbisfile and the application using
	libvorbisfile are not linked against the exact same
	version/variant/build of crt.o (and they usually won't be, especially
	using a prebuilt libvorbis DLL), <tt>FILE *</tt> handles cannot be
	opened in the application and then passed to vorbisfile to be used
	by stdio calls from vorbisfile's different version of CRT. For this
	reason, using <a href="ov_open.html">ov_open()</a> under Windows
	without careful, expert linking will typically cause a protection
	fault. Windows programmers should use <a
	href="ov_fopen.html">ov_fopen()</a> (which will only use libvorbis's
	crt.o) or <a href="ov_open_callbacks.html">ov_open_callbacks()</a>
	(which will only use the application's crt.o) instead.<p>

	This warning only applies to Windows and only applies to <a
	href="ov_open.html">ov_open()</a>. It is perfectly safe to use <a
	href="ov_open.html">ov_open()</a> on all other platforms.<p>

	For more information, see the following microsoft pages on <a
	href="http://msdn2.microsoft.com/en-us/library/abx4dbyh(VS.80).aspx">C
	runtime library linking</a> and a specific description of <a
	href="http://msdn2.microsoft.com/en-us/library/ms235460(VS.80).aspx">restrictions
	on passing CRT objects across DLL boundaries</a>.

	<p>

	<dt><b>[b] Threaded decode</b><p>
	<dd>If your decoder is threaded, it is recommended that you NOT call
	<tt>ov_open()</tt>
	in the main control thread--instead, call <tt>ov_open()</tt> in your decode/playback
	thread. This is important because <tt>ov_open()</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>