Tremor/doc/ov_open.html

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   4 <title>Tremor - function - ov_open</title>
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  11 <td><p class=tiny>Tremor documentation</p></td>
  12 <td align=right><p class=tiny>Tremor version 1.0 - 20020403</p></td>
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  15
  16 <h1>ov_open</h1>
  17
  18 <p><i>declared in "ivorbisfile.h";</i></p>
  19
  20 <p>This is the main function used to open and initialize an OggVorbis_File
  21 structure. It sets up all the related decoding structure.
  22 <p>The first argument must be a file pointer to an already opened file
  23 or pipe (it need not be seekable--though this obviously restricts what
  24 can be done with the bitstream). <tt>vf</tt> should be a pointer to the
  25 OggVorbis_File structure--this is used for ALL the externally visible libvorbisidec
  26 functions. Once this has been called, the same <a href="OggVorbis_File.html">OggVorbis_File</a>
  27 struct should be passed to all the libvorbisidec functions.
  28 <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.
  29 <p>
  30 It is often useful to call <tt>ov_open()</tt>
  31 simply to determine whether a given file is a vorbis bitstream. If the
  32 <tt>ov_open()</tt>
  33 call fails, then the file is not recognizable as such.
  34 When you use <tt>ov_open()
  35 </tt>for
  36 this, you should <tt>fclose()</tt> the file pointer if, and only if, the
  37 <tt>ov_open()</tt>
  38 call fails. If it succeeds, you must call <a href="ov_clear.html">ov_clear()</a> to clear
  39 the decoder's buffers and close the file for you.<p>
  40
  41 (Note that <a href="ov_test.html">ov_test()</a> provides a less expensive way to test a file for Vorbisness.)<p>
  42
  43 <br><br>
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  47 <pre><b>
  48 int ov_open(FILE *f,<a href="OggVorbis_File.html">OggVorbis_File</a> *vf,char *initial,long ibytes);
  49 </b></pre>
  50         </td>
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  53
  54 <h3>Parameters</h3>
  55 <dl>
  56 <dt><i>f</i></dt>
  57 <dd>File pointer to an already opened file
  58 or pipe (it need not be seekable--though this obviously restricts what
  59 can be done with the bitstream).</dd>
  60 <dt><i>vf</i></dt>
  61 <dd>A pointer to the OggVorbis_File structure--this is used for ALL the externally visible libvorbisidec
  62 functions. Once this has been called, the same <tt>OggVorbis_File</tt>
  63 struct should be passed to all the libvorbisidec functions.</dd>
  64 <dt><i>initial</i></dt>
  65 <dd>Typically set to NULL.  This parameter is useful if some data has already been
  66 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>
  67 should be a pointer to a buffer containing the data read.</dd>
  68 <dt><i>ibytes</i></dt>
  69 <dd>Typically set to 0.  This parameter is useful if some data has already been
  70 read from the file and the stream is not seekable. In this case, <tt>ibytes</tt>
  71 should contain the length (in bytes) of the buffer.  Used together with <tt>initial</tt></dd>
  72 </dl>
  73
  74
  75 <h3>Return Values</h3>
  76 <blockquote>
  77 <li>0 indicates success</li>
  78
  79 <li>less than zero for failure:</li>
  80 <ul>
  81 <li>OV_EREAD - A read from media returned an error.</li>
  82 <li>OV_ENOTVORBIS - Bitstream is not Vorbis data.</li>
  83 <li>OV_EVERSION - Vorbis version mismatch.</li>
  84 <li>OV_EBADHEADER - Invalid Vorbis bitstream header.</li>
  85 <li>OV_EFAULT - Internal logic fault; indicates a bug or heap/stack corruption.</li>
  86 </ul>
  87 </blockquote>
  88 <p>
  89
  90 <h3>Notes</h3>
  91 <p>If your decoder is threaded, it is recommended that you NOT call
  92 <tt>ov_open()</tt>
  93 in the main control thread--instead, call <tt>ov_open()</tt> IN your decode/playback
  94 thread. This is important because <tt>ov_open()</tt> may be a fairly time-consuming
  95 call, given that the full structure of the file is determined at this point,
  96 which may require reading large parts of the file under certain circumstances
  97 (determining all the logical bitstreams in one physical bitstream, for
  98 example).  See <a href="threads.html">Thread Safety</a> for other information on using libvorbisidec with threads.
  99
 100
 101 <br><br>
 102 <hr noshade>
 103 <table border=0 width=100%>
 104 <tr valign=top>
 105 <td><p class=tiny>copyright &copy; 2002 Xiph.org</p></td>
 106 <td align=right><p class=tiny><a href="http://www.xiph.org/ogg/vorbis/">Ogg Vorbis</a></p></td>
 107 </tr><tr>
 108 <td><p class=tiny>Tremor documentation</p></td>
 109 <td align=right><p class=tiny>Tremor version 1.0 - 20020403</p></td>
 110 </tr>
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