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3 <head>
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4 <title>Vorbisfile - function - ov_open</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</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>ov_open is one of three initialization functions used to initialize
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21 an OggVorbis_File structure and prepare a bitstream for playback.
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22
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23 <p><em><b> WARNING for Windows developers: </b> Do not use ov_open() in
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24 Windows applications; Windows linking places restrictions on
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25 passing <tt>FILE *</tt> handles successfully, and ov_open() runs
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26 afoul of these restrictions <a href="#winfoot">[a]</a>. See the <a
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27 href="ov_open_callbacks.html">ov_open_callbacks() page </a> for
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28 details on using <a
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29 href="ov_open_callbacks.html">ov_open_callbacks()</a> instead. </em>
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30
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31 <p>The first argument must be a file pointer to an already opened file
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32 or pipe (it need not be seekable--though this obviously restricts what
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33 can be done with the bitstream). <tt>vf</tt> should be a pointer to the
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34 OggVorbis_File structure -- this is used for ALL the externally visible libvorbisfile
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35 functions. Once this has been called, the same <a href="OggVorbis_File.html">OggVorbis_File</a>
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36 struct should be passed to all the libvorbisfile functions.<p>
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37
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38 The <tt>vf</tt> structure initialized using ov_fopen() must eventually
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39 be cleaned using <a href="ov_clear.html">ov_clear()</a>. Once a
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40 <tt>FILE *</tt> handle is passed to ov_open() successfully, the
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41 application MUST NOT <tt>fclose()</tt> or in any other way manipulate
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42 that file handle. Vorbisfile will close the file in <a
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43 href="ov_clear.html">ov_clear()</a>. If the application must be able
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44 to close the <tt>FILE *</tt> handle itself, see <a
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45 href="ov_open_callbacks.html">ov_open_callbacks()</a> with the use of
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46 <tt>OV_CALLBACKS_NOCLOSE</tt>.
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47
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48 <p>It is often useful to call <tt>ov_open()</tt> simply to determine
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49 whether a given file is a Vorbis bitstream. If the <tt>ov_open()</tt>
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50 call fails, then the file is not recognizable as Vorbis. If the call
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51 succeeds but the initialized <tt>vf</tt> structure will not be used,
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52 the application is responsible for calling <a
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53 href="ov_clear.html">ov_clear()</a> to clear the decoder's buffers and
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54 close the file.<p>
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55
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56 If [and only if] an <tt>ov_open()</tt> call fails, the application
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57 must explicitly <tt>fclose()</tt> the <tt>FILE *</tt> pointer itself.
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58
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59
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60 <br><br>
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61 <table border=0 color=black cellspacing=0 cellpadding=7>
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62 <tr bgcolor=#cccccc>
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63 <td>
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64 <pre><b>
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65 int ov_open(FILE *f,<a href="OggVorbis_File.html">OggVorbis_File</a> *vf,char *initial,long ibytes);
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66 </b></pre>
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67 </td>
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68 </tr>
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69 </table>
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70
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71 <h3>Parameters</h3>
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72 <dl>
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73 <dt><i>f</i></dt>
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74 <dd>File pointer to an already opened file
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75 or pipe (it need not be seekable--though this obviously restricts what
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76 can be done with the bitstream).</dd>
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77 <dt><i>vf</i></dt>
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78 <dd>A pointer to the OggVorbis_File structure--this is used for ALL the externally visible libvorbisfile
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79 functions. Once this has been called, the same <tt>OggVorbis_File</tt>
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80 struct should be passed to all the libvorbisfile functions.</dd>
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81 <dt><i>initial</i></dt>
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82 <dd>Typically set to NULL. This parameter is useful if some data has already been
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83 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>
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84 should be a pointer to a buffer containing the data read.</dd>
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85 <dt><i>ibytes</i></dt>
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86 <dd>Typically set to 0. This parameter is useful if some data has already been
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87 read from the file and the stream is not seekable. In this case, <tt>ibytes</tt>
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88 should contain the length (in bytes) of the buffer. Used together with <tt>initial</tt></dd>
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89 </dl>
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90
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91
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92 <h3>Return Values</h3>
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93 <blockquote>
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94 <li>0 indicates success</li>
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95
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96 <li>less than zero for failure:</li>
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97 <ul>
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98 <li>OV_EREAD - A read from media returned an error.</li>
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99 <li>OV_ENOTVORBIS - Bitstream is not Vorbis data.</li>
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100 <li>OV_EVERSION - Vorbis version mismatch.</li>
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101 <li>OV_EBADHEADER - Invalid Vorbis bitstream header.</li>
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102 <li>OV_EFAULT - Internal logic fault; indicates a bug or heap/stack corruption.</li>
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103 </ul>
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104 </blockquote>
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105 <p>
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106
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107 <a name="notes"></a>
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108 <h3>Notes</h3>
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109 <dl>
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110
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111 <a name="winfoot"></a>
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112 <dt><b>[a] Windows and ov_open()</b><p>
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113
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114 <dd>Under Windows, stdio file access is implemented in each of many
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115 variants of crt.o, several of which are typically installed on any one
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116 Windows machine. If libvorbisfile and the application using
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117 libvorbisfile are not linked against the exact same
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118 version/variant/build of crt.o (and they usually won't be, especially
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119 using a prebuilt libvorbis DLL), <tt>FILE *</tt> handles cannot be
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120 opened in the application and then passed to vorbisfile to be used
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121 by stdio calls from vorbisfile's different version of CRT. For this
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122 reason, using <a href="ov_open.html">ov_open()</a> under Windows
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123 without careful, expert linking will typically cause a protection
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124 fault. Windows programmers should use <a
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125 href="ov_fopen.html">ov_fopen()</a> (which will only use libvorbis's
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126 crt.o) or <a href="ov_open_callbacks.html">ov_open_callbacks()</a>
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127 (which will only use the application's crt.o) instead.<p>
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128
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129 This warning only applies to Windows and only applies to <a
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130 href="ov_open.html">ov_open()</a>. It is perfectly safe to use <a
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131 href="ov_open.html">ov_open()</a> on all other platforms.<p>
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132
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133 For more information, see the following microsoft pages on <a
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134 href="http://msdn2.microsoft.com/en-us/library/abx4dbyh(VS.80).aspx">C
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135 runtime library linking</a> and a specific description of <a
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136 href="http://msdn2.microsoft.com/en-us/library/ms235460(VS.80).aspx">restrictions
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137 on passing CRT objects across DLL boundaries</a>.
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138
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139 <p>
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140
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141 <dt><b>[b] Threaded decode</b><p>
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142 <dd>If your decoder is threaded, it is recommended that you NOT call
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143 <tt>ov_open()</tt>
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144 in the main control thread--instead, call <tt>ov_open()</tt> in your decode/playback
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145 thread. This is important because <tt>ov_open()</tt> may be a fairly time-consuming
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146 call, given that the full structure of the file is determined at this point,
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147 which may require reading large parts of the file under certain circumstances
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148 (determining all the logical bitstreams in one physical bitstream, for
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149 example). See <a href="threads.html">Thread Safety</a> for other information on using libvorbisfile with threads.
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150 <p>
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151
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152 <dt><b>[c] Mixed media streams</b><p>
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153 <dd>
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154 As of Vorbisfile release 1.2.0, Vorbisfile is able to access the
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155 Vorbis content in mixed-media Ogg streams, not just Vorbis-only
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156 streams. For example, Vorbisfile may be used to open and access the
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157 audio from an Ogg stream consisting of Theora video and Vorbis audio.
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158 Vorbisfile 1.2.0 decodes the first logical audio stream of each
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159 physical stream section.<p>
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160
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161 <dt><b>[d] Faster testing for Vorbis files</b><p>
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162 <dd><a href="ov_test.html">ov_test()</a> and <a
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163 href="ov_test_callbacks.html">ov_test_callbacks()</a> provide less
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164 computationally expensive ways to test a file for Vorbisness, but
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165 require more setup code.<p>
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166
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167 </dl>
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168
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169 <br><br>
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170 <hr noshade>
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171 <table border=0 width=100%>
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172 <tr valign=top>
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173 <td><p class=tiny>copyright © 2000-2010 Xiph.Org</p></td>
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174 <td align=right><p class=tiny><a href="http://www.xiph.org/ogg/vorbis/">Ogg Vorbis</a></p></td>
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175 </tr><tr>
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176 <td><p class=tiny>Vorbisfile documentation</p></td>
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177 <td align=right><p class=tiny>vorbisfile version 1.3.2 - 20101101</p></td>
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178 </tr>
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179 </table>
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180
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181 </body>
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182
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183 </html>
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