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authorAki <please@ignore.pl>2021-09-29 22:52:49 +0200
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+<html>
+
+<head>
+<title>Vorbisfile - Callbacks and non-stdio I/O</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>Callbacks and non-stdio I/O</h1>
+
+Although stdio is convenient and nearly universally implemented as per
+ANSI C, it is not suited to all or even most potential uses of Vorbis.
+For additional flexibility, embedded applications may provide their
+own I/O functions for use with Vorbisfile when stdio is unavailable or not
+suitable. One common example is decoding a Vorbis stream from a
+memory buffer.<p>
+
+Use custom I/O functions by populating an <a
+href="ov_callbacks.html">ov_callbacks</a> structure and calling <a
+href="ov_open_callbacks.html">ov_open_callbacks()</a> or <a
+href="ov_test_callbacks.html">ov_test_callbacks()</a> rather than the
+typical <a href="ov_open.html">ov_open()</a> or <a
+href="ov_test.html">ov_test()</a>. Past the open call, use of
+libvorbisfile is identical to using it with stdio.
+
+<h2>Read function</h2>
+
+The read-like function provided in the <tt>read_func</tt> field is
+used to fetch the requested amount of data. It expects the fetch
+operation to function similar to file-access, that is, a multiple read
+operations will retrieve contiguous sequential pieces of data,
+advancing a position cursor after each read.<p>
+
+The following behaviors are also expected:<p>
+<ul>
+<li>a return of '0' indicates end-of-data (if the by-thread errno is unset)
+<li>short reads mean nothing special (short reads are not treated as error conditions)
+<li>a return of zero with the by-thread errno set to nonzero indicates a read error
+</ul>
+<p>
+
+<h2>Seek function</h2>
+
+The seek-like function provided in the <tt>seek_func</tt> field is
+used to request non-sequential data access by libvorbisfile, moving
+the access cursor to the requested position. The seek function is
+optional; if callbacks are only to handle non-seeking (streaming) data
+or the application wishes to force streaming behavior,
+<tt>seek_func</tt> and <tt>tell_func</tt> should be set to NULL. If
+the seek function is non-NULL, libvorbisfile mandates the following
+behavior:
+
+<ul>
+<li>The seek function must always return -1 (failure) if the given
+data abstraction is not seekable. It may choose to always return -1
+if the application desires libvorbisfile to treat the Vorbis data
+strictly as a stream (which makes for a less expensive open
+operation).<p>
+
+<li>If the seek function initially indicates seekability, it must
+always succeed upon being given a valid seek request.<p>
+
+<li>The seek function must implement all of SEEK_SET, SEEK_CUR and
+SEEK_END. The implementation of SEEK_END should set the access cursor
+one past the last byte of accessible data, as would stdio
+<tt>fseek()</tt><p>
+</ul>
+
+<h2>Close function</h2>
+
+The close function should deallocate any access state used by the
+passed in instance of the data access abstraction and invalidate the
+instance handle. The close function is assumed to succeed; its return
+code is not checked.<p>
+
+The <tt>close_func</tt> may be set to NULL to indicate that libvorbis
+should not attempt to close the file/data handle in <a
+href="ov_clear.html">ov_clear</a> but allow the application to handle
+file/data access cleanup itself. For example, by passing the normal
+stdio calls as callback functions, but passing a <tt>close_func</tt>
+that is NULL or does nothing (as in the case of OV_CALLBACKS_NOCLOSE), an
+application may call <a href="ov_clear.html">ov_clear()</a> and then
+later <tt>fclose()</tt> the file originally passed to libvorbisfile.
+
+<h2>Tell function</h2>
+
+The tell function is intended to mimic the
+behavior of <tt>ftell()</tt> and must return the byte position of the
+next data byte that would be read. If the data access cursor is at
+the end of the 'file' (pointing to one past the last byte of data, as
+it would be after calling <tt>fseek(file,SEEK_END,0)</tt>), the tell
+function must return the data position (and thus the total file size),
+not an error.<p>
+
+The tell function need not be provided if the data IO abstraction is
+not seekable, or the application wishes to force streaming
+behavior. In this case, the <tt>tell_func</tt> and <tt>seek_func</tt>
+fields should be set to NULL.<p>
+
+<br><br>
+<hr noshade>
+<table border=0 width=100%>
+<tr valign=top>
+<td><p class=tiny>copyright &copy; 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>