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comparison src/libvorbis-1.3.3/doc/vorbisfile/ov_open.html @ 1:05aa0afa9217
Bring in flac, ogg, vorbis
| author | Chris Cannam |
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| date | Tue, 19 Mar 2013 17:37:49 +0000 |
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| 0:c7265573341e | 1:05aa0afa9217 |
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| 1 <html> | |
| 2 | |
| 3 <head> | |
| 4 <title>Vorbisfile - function - ov_open</title> | |
| 5 <link rel=stylesheet href="style.css" type="text/css"> | |
| 6 </head> | |
| 7 | |
| 8 <body bgcolor=white text=black link="#5555ff" alink="#5555ff" vlink="#5555ff"> | |
| 9 <table border=0 width=100%> | |
| 10 <tr> | |
| 11 <td><p class=tiny>Vorbisfile documentation</p></td> | |
| 12 <td align=right><p class=tiny>vorbisfile version 1.3.2 - 20101101</p></td> | |
| 13 </tr> | |
| 14 </table> | |
| 15 | |
| 16 <h1>ov_open</h1> | |
| 17 | |
| 18 <p><i>declared in "vorbis/vorbisfile.h";</i></p> | |
| 19 | |
| 20 <p>ov_open is one of three initialization functions used to initialize | |
| 21 an OggVorbis_File structure and prepare a bitstream for playback. | |
| 22 | |
| 23 <p><em><b> WARNING for Windows developers: </b> Do not use ov_open() in | |
| 24 Windows applications; Windows linking places restrictions on | |
| 25 passing <tt>FILE *</tt> handles successfully, and ov_open() runs | |
| 26 afoul of these restrictions <a href="#winfoot">[a]</a>. See the <a | |
| 27 href="ov_open_callbacks.html">ov_open_callbacks() page </a> for | |
| 28 details on using <a | |
| 29 href="ov_open_callbacks.html">ov_open_callbacks()</a> instead. </em> | |
| 30 | |
| 31 <p>The first argument must be a file pointer to an already opened file | |
| 32 or pipe (it need not be seekable--though this obviously restricts what | |
| 33 can be done with the bitstream). <tt>vf</tt> should be a pointer to the | |
| 34 OggVorbis_File structure -- this is used for ALL the externally visible libvorbisfile | |
| 35 functions. Once this has been called, the same <a href="OggVorbis_File.html">OggVorbis_File</a> | |
| 36 struct should be passed to all the libvorbisfile functions.<p> | |
| 37 | |
| 38 The <tt>vf</tt> structure initialized using ov_fopen() must eventually | |
| 39 be cleaned using <a href="ov_clear.html">ov_clear()</a>. Once a | |
| 40 <tt>FILE *</tt> handle is passed to ov_open() successfully, the | |
| 41 application MUST NOT <tt>fclose()</tt> or in any other way manipulate | |
| 42 that file handle. Vorbisfile will close the file in <a | |
| 43 href="ov_clear.html">ov_clear()</a>. If the application must be able | |
| 44 to close the <tt>FILE *</tt> handle itself, see <a | |
| 45 href="ov_open_callbacks.html">ov_open_callbacks()</a> with the use of | |
| 46 <tt>OV_CALLBACKS_NOCLOSE</tt>. | |
| 47 | |
| 48 <p>It is often useful to call <tt>ov_open()</tt> simply to determine | |
| 49 whether a given file is a Vorbis bitstream. If the <tt>ov_open()</tt> | |
| 50 call fails, then the file is not recognizable as Vorbis. If the call | |
| 51 succeeds but the initialized <tt>vf</tt> structure will not be used, | |
| 52 the application is responsible for calling <a | |
| 53 href="ov_clear.html">ov_clear()</a> to clear the decoder's buffers and | |
| 54 close the file.<p> | |
| 55 | |
| 56 If [and only if] an <tt>ov_open()</tt> call fails, the application | |
| 57 must explicitly <tt>fclose()</tt> the <tt>FILE *</tt> pointer itself. | |
| 58 | |
| 59 | |
| 60 <br><br> | |
| 61 <table border=0 color=black cellspacing=0 cellpadding=7> | |
| 62 <tr bgcolor=#cccccc> | |
| 63 <td> | |
| 64 <pre><b> | |
| 65 int ov_open(FILE *f,<a href="OggVorbis_File.html">OggVorbis_File</a> *vf,char *initial,long ibytes); | |
| 66 </b></pre> | |
| 67 </td> | |
| 68 </tr> | |
| 69 </table> | |
| 70 | |
| 71 <h3>Parameters</h3> | |
| 72 <dl> | |
| 73 <dt><i>f</i></dt> | |
| 74 <dd>File pointer to an already opened file | |
| 75 or pipe (it need not be seekable--though this obviously restricts what | |
| 76 can be done with the bitstream).</dd> | |
| 77 <dt><i>vf</i></dt> | |
| 78 <dd>A pointer to the OggVorbis_File structure--this is used for ALL the externally visible libvorbisfile | |
| 79 functions. Once this has been called, the same <tt>OggVorbis_File</tt> | |
| 80 struct should be passed to all the libvorbisfile functions.</dd> | |
| 81 <dt><i>initial</i></dt> | |
| 82 <dd>Typically set to NULL. This parameter is useful if some data has already been | |
| 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> | |
| 84 should be a pointer to a buffer containing the data read.</dd> | |
| 85 <dt><i>ibytes</i></dt> | |
| 86 <dd>Typically set to 0. This parameter is useful if some data has already been | |
| 87 read from the file and the stream is not seekable. In this case, <tt>ibytes</tt> | |
| 88 should contain the length (in bytes) of the buffer. Used together with <tt>initial</tt></dd> | |
| 89 </dl> | |
| 90 | |
| 91 | |
| 92 <h3>Return Values</h3> | |
| 93 <blockquote> | |
| 94 <li>0 indicates success</li> | |
| 95 | |
| 96 <li>less than zero for failure:</li> | |
| 97 <ul> | |
| 98 <li>OV_EREAD - A read from media returned an error.</li> | |
| 99 <li>OV_ENOTVORBIS - Bitstream is not Vorbis data.</li> | |
| 100 <li>OV_EVERSION - Vorbis version mismatch.</li> | |
| 101 <li>OV_EBADHEADER - Invalid Vorbis bitstream header.</li> | |
| 102 <li>OV_EFAULT - Internal logic fault; indicates a bug or heap/stack corruption.</li> | |
| 103 </ul> | |
| 104 </blockquote> | |
| 105 <p> | |
| 106 | |
| 107 <a name="notes"></a> | |
| 108 <h3>Notes</h3> | |
| 109 <dl> | |
| 110 | |
| 111 <a name="winfoot"></a> | |
| 112 <dt><b>[a] Windows and ov_open()</b><p> | |
| 113 | |
| 114 <dd>Under Windows, stdio file access is implemented in each of many | |
| 115 variants of crt.o, several of which are typically installed on any one | |
| 116 Windows machine. If libvorbisfile and the application using | |
| 117 libvorbisfile are not linked against the exact same | |
| 118 version/variant/build of crt.o (and they usually won't be, especially | |
| 119 using a prebuilt libvorbis DLL), <tt>FILE *</tt> handles cannot be | |
| 120 opened in the application and then passed to vorbisfile to be used | |
| 121 by stdio calls from vorbisfile's different version of CRT. For this | |
| 122 reason, using <a href="ov_open.html">ov_open()</a> under Windows | |
| 123 without careful, expert linking will typically cause a protection | |
| 124 fault. Windows programmers should use <a | |
| 125 href="ov_fopen.html">ov_fopen()</a> (which will only use libvorbis's | |
| 126 crt.o) or <a href="ov_open_callbacks.html">ov_open_callbacks()</a> | |
| 127 (which will only use the application's crt.o) instead.<p> | |
| 128 | |
| 129 This warning only applies to Windows and only applies to <a | |
| 130 href="ov_open.html">ov_open()</a>. It is perfectly safe to use <a | |
| 131 href="ov_open.html">ov_open()</a> on all other platforms.<p> | |
| 132 | |
| 133 For more information, see the following microsoft pages on <a | |
| 134 href="http://msdn2.microsoft.com/en-us/library/abx4dbyh(VS.80).aspx">C | |
| 135 runtime library linking</a> and a specific description of <a | |
| 136 href="http://msdn2.microsoft.com/en-us/library/ms235460(VS.80).aspx">restrictions | |
| 137 on passing CRT objects across DLL boundaries</a>. | |
| 138 | |
| 139 <p> | |
| 140 | |
| 141 <dt><b>[b] Threaded decode</b><p> | |
| 142 <dd>If your decoder is threaded, it is recommended that you NOT call | |
| 143 <tt>ov_open()</tt> | |
| 144 in the main control thread--instead, call <tt>ov_open()</tt> in your decode/playback | |
| 145 thread. This is important because <tt>ov_open()</tt> may be a fairly time-consuming | |
| 146 call, given that the full structure of the file is determined at this point, | |
| 147 which may require reading large parts of the file under certain circumstances | |
| 148 (determining all the logical bitstreams in one physical bitstream, for | |
| 149 example). See <a href="threads.html">Thread Safety</a> for other information on using libvorbisfile with threads. | |
| 150 <p> | |
| 151 | |
| 152 <dt><b>[c] Mixed media streams</b><p> | |
| 153 <dd> | |
| 154 As of Vorbisfile release 1.2.0, Vorbisfile is able to access the | |
| 155 Vorbis content in mixed-media Ogg streams, not just Vorbis-only | |
| 156 streams. For example, Vorbisfile may be used to open and access the | |
| 157 audio from an Ogg stream consisting of Theora video and Vorbis audio. | |
| 158 Vorbisfile 1.2.0 decodes the first logical audio stream of each | |
| 159 physical stream section.<p> | |
| 160 | |
| 161 <dt><b>[d] Faster testing for Vorbis files</b><p> | |
| 162 <dd><a href="ov_test.html">ov_test()</a> and <a | |
| 163 href="ov_test_callbacks.html">ov_test_callbacks()</a> provide less | |
| 164 computationally expensive ways to test a file for Vorbisness, but | |
| 165 require more setup code.<p> | |
| 166 | |
| 167 </dl> | |
| 168 | |
| 169 <br><br> | |
| 170 <hr noshade> | |
| 171 <table border=0 width=100%> | |
| 172 <tr valign=top> | |
| 173 <td><p class=tiny>copyright © 2000-2010 Xiph.Org</p></td> | |
| 174 <td align=right><p class=tiny><a href="http://www.xiph.org/ogg/vorbis/">Ogg Vorbis</a></p></td> | |
| 175 </tr><tr> | |
| 176 <td><p class=tiny>Vorbisfile documentation</p></td> | |
| 177 <td align=right><p class=tiny>vorbisfile version 1.3.2 - 20101101</p></td> | |
| 178 </tr> | |
| 179 </table> | |
| 180 | |
| 181 </body> | |
| 182 | |
| 183 </html> |