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3 <head>
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4 <title>Vorbisfile - function - ov_open_callbacks</title>
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5 <link rel=stylesheet href="style.css" type="text/css">
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6 </head>
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7
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8 <body bgcolor=white text=black link="#5555ff" alink="#5555ff" vlink="#5555ff">
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9 <table border=0 width=100%>
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10 <tr>
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11 <td><p class=tiny>Vorbisfile documentation</p></td>
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12 <td align=right><p class=tiny>vorbisfile version 1.3.2 - 20101101</p></td>
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13 </tr>
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14 </table>
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15
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16 <h1>ov_open_callbacks</h1>
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17
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18 <p><i>declared in "vorbis/vorbisfile.h";</i></p>
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19
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20 <p>This is an alternative function used to open and initialize an
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21 OggVorbis_File structure when using a data source other than a file,
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22 when its necessary to modify default file access behavior, or to
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23 initialize a Vorbis decode from a <tt>FILE *</tt> pointer under
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24 Windows where <a href="ov_open.html">ov_open()</a> cannot be used. It
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25 allows the application to specify custom file manipulation routines
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26 and sets up all the related decoding structures.
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27
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28 <p>Once ov_open_callbacks() has been called, the same
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29 <tt>OggVorbis_File</tt> struct should be passed to all the
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30 libvorbisfile functions. Unlike <a
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31 href="ov_fopen.html">ov_fopen()</a> and <a
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32 href="ov_open.html">ov_open()</a>, ov_open_callbacks() may be used to
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33 instruct vorbisfile to either automatically close or not to close the
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34 file/data access handle in <a href="ov_clear.html">ov_clear()</a>.
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35 Automatic closure is disabled by passing NULL as the close callback,
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36 or using one of the predefined callback sets that specify a NULL close
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37 callback. The application is responsible for closing a file when a
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38 call to ov_open_callbacks() is unsuccessful.<p>
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39
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40 See also <a href="callbacks.html">Callbacks and Non-stdio I/O</a> for
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41 information on designing and specifying custom callback functions.<p>
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42
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43 <br><br>
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44 <table border=0 color=black cellspacing=0 cellpadding=7>
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45 <tr bgcolor=#cccccc>
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46 <td>
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47 <pre><b>
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48 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);
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49 </b></pre>
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50 </td>
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51 </tr>
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52 </table>
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53
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54 <h3>Parameters</h3>
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55 <dl>
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56 <dt><i>datasource</i></dt>
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57 <dd>Pointer to a data structure allocated by the calling application, containing any state needed by the callbacks provided.</dd>
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58 <dt><i>vf</i></dt>
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59 <dd>A pointer to the OggVorbis_File structure--this is used for ALL the externally visible libvorbisfile
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60 functions. Once this has been called, the same <tt>OggVorbis_File</tt>
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61 struct should be passed to all the libvorbisfile functions.</dd>
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62 <dt><i>initial</i></dt>
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63 <dd>Typically set to NULL. This parameter is useful if some data has already been
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64 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>
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65 should be a pointer to a buffer containing the data read.</dd>
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66 <dt><i>ibytes</i></dt>
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67 <dd>Typically set to 0. This parameter is useful if some data has already been
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68 read from the stream and the stream is not seekable. In this case, <tt>ibytes</tt>
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69 should contain the length (in bytes) of the buffer. Used together with <tt>initial</tt>.</dd>
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70 <dt><i>callbacks</i></dt>
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71 <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>
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72 </dl>
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73
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74
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75 <h3>Return Values</h3>
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76 <blockquote>
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77 <li>0 for success</li>
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78 <li>less than zero for failure:</li>
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79 <ul>
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80 <li>OV_EREAD - A read from media returned an error.</li>
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81 <li>OV_ENOTVORBIS - Bitstream does not contain any Vorbis data.</li>
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82 <li>OV_EVERSION - Vorbis version mismatch.</li>
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83 <li>OV_EBADHEADER - Invalid Vorbis bitstream header.</li>
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84 <li>OV_EFAULT - Internal logic fault; indicates a bug or heap/stack corruption.</li>
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85 </ul>
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86 </blockquote>
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87 <p>
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88
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89 <h3>Notes</h3>
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90 <dl>
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91
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92 <dt><b>[a] Windows and use as an ov_open() substitute</b><p> Windows
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93 applications should not use <a href="ov_open.html">ov_open()</a> due
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94 to the likelihood of <a href="ov_open.html#winfoot">CRT linking
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95 mismatches and runtime protection faults
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96 [ov_open:a]</a>. ov_open_callbacks() is a safe substitute; specifically:
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97
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98 <pre><tt>ov_open_callbacks(f, vf, initial, ibytes, OV_CALLBACKS_DEFAULT);</tt>
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99 </pre>
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100
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101 ... provides exactly the same functionality as <a
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102 href="ov_open.html">ov_open()</a> but will always work correctly under
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103 Windows, regardless of linking setup details.<p>
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104
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105 <dt><b>[b] Threaded decode</b><p>
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106 <dd>If your decoder is threaded, it is recommended that you NOT call
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107 <tt>ov_open_callbacks()</tt>
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108 in the main control thread--instead, call <tt>ov_open_callbacks()</tt> in your decode/playback
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109 thread. This is important because <tt>ov_open_callbacks()</tt> may be a fairly time-consuming
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110 call, given that the full structure of the file is determined at this point,
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111 which may require reading large parts of the file under certain circumstances
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112 (determining all the logical bitstreams in one physical bitstream, for
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113 example). See <a href="threads.html">Thread Safety</a> for other information on using libvorbisfile with threads.
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114 <p>
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115
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116 <dt><b>[c] Mixed media streams</b><p>
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117 <dd>
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118 As of Vorbisfile release 1.2.0, Vorbisfile is able to access the
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119 Vorbis content in mixed-media Ogg streams, not just Vorbis-only
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120 streams. For example, Vorbisfile may be used to open and access the
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121 audio from an Ogg stream consisting of Theora video and Vorbis audio.
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122 Vorbisfile 1.2.0 decodes the first logical audio stream of each
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123 physical stream section.<p>
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124
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125 <dt><b>[d] Faster testing for Vorbis files</b><p>
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126 <dd><a href="ov_test.html">ov_test()</a> and <a
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127 href="ov_test_callbacks.html">ov_test_callbacks()</a> provide less
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128 computationally expensive ways to test a file for Vorbisness, but
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129 require more setup code.<p>
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130
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131 </dl>
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132
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133 <br><br>
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134 <hr noshade>
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135 <table border=0 width=100%>
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136 <tr valign=top>
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137 <td><p class=tiny>copyright © 2000-2010 Xiph.Org</p></td>
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138 <td align=right><p class=tiny><a href="http://www.xiph.org/ogg/vorbis/">Ogg Vorbis</a></p></td>
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139 </tr><tr>
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140 <td><p class=tiny>Vorbisfile documentation</p></td>
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141 <td align=right><p class=tiny>vorbisfile version 1.3.2 - 20101101</p></td>
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142 </tr>
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143 </table>
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144
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145 </body>
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146
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147 </html>
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