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| author | Aki <please@ignore.pl> | 2021-09-29 22:52:49 +0200 |
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| committer | Aki <please@ignore.pl> | 2021-09-29 22:52:49 +0200 |
| commit | 74f4b1bc3b627ba4c7e03498234d88cacdfbe97b (patch) | |
| tree | 197b5978d6e38f44069ea92583098a1da04aa635 /doc/vorbisfile/ov_open.html | |
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diff --git a/doc/vorbisfile/ov_open.html b/doc/vorbisfile/ov_open.html new file mode 100644 index 0000000..d0311ce --- /dev/null +++ b/doc/vorbisfile/ov_open.html @@ -0,0 +1,183 @@ +<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 1.3.2 - 20101101</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 © 2000-2010 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 1.3.2 - 20101101</p></td> +</tr> +</table> + +</body> + +</html> |