| [16] | 1 | <html> |
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| 2 | |
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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 1.2.0 - 20070723</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 © 2007 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 1.2.0 - 20070723</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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