1 <html> 2 3 <head> 4 <title>Vorbisfile - Decoding</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 1.2.0 - 20070723</p></td> 13 </tr> 14 </table> 15 16 <h1>Decoding</h1> 17 18 <p> 19 All libvorbisfile decoding routines are declared in "vorbis/vorbisfile.h". 20 <p> 21 22 After <a href="initialization.html">initialization</a>, decoding audio 23 is as simple as calling <a href="ov_read.html">ov_read()</a> (or the 24 similar functions <a href="ov_read_float.html">ov_read_float()</a> and 25 <a href="ov_read_filter.html">ov_read_filter</a>). This function works 26 similarly to reading from a normal file using <tt>read()</tt>.<p> 27 28 However, a few differences are worth noting: 29 30 <h2>multiple stream links</h2> 31 32 A Vorbis stream may consist of multiple sections (called links) that 33 encode differing numbers of channels or sample rates. It is vitally 34 important to pay attention to the link numbers returned by <a 35 href="ov_read.html">ov_read</a> and handle audio changes that may 36 occur at link boundaries. Such multi-section files do exist in the 37 wild and are not merely a specification curiosity. 38 39 <h2>returned data amount</h2> 40 41 <a href="ov_read.html">ov_read</a> does not attempt to completely fill 42 a large, passed in data buffer; it merely guarantees that the passed 43 back data does not overflow the passed in buffer size. Large buffers 44 may be filled by iteratively looping over calls to <a 45 href="ov_read.html">ov_read</a> (incrementing the buffer pointer) 46 until the original buffer is filled. 47 48 <h2>file cursor position</h2> 49 50 Vorbis files do not necessarily start at a sample number or time offset 51 of zero. Do not be surprised if a file begins at a positive offset of 52 several minutes or hours, such as would happen if a large stream (such 53 as a concert recording) is chopped into multiple seperate files. 54 55 <p> 56 <table border=1 color=black width=50% cellspacing=0 cellpadding=7> 57 <tr bgcolor=#cccccc> 58 <td><b>function</b></td> 59 <td><b>purpose</b></td> 60 </tr> 61 <tr valign=top> 62 <td><a href="ov_read.html">ov_read</a></td> 63 <td>This function makes up the main chunk of a decode loop. It takes an 64 OggVorbis_File structure, which must have been initialized by a previous 65 call to <a href="ov_open.html"><tt>ov_open()</tt></a>, <a href="ov_fopen.html"><tt>ov_fopen()</tt></a>, 66 or <a href="ov_open_callbacks.html"><tt>ov_open_callbacks()</tt></a>.</td> 67 </tr> 68 <tr valign=top> 69 <td><a href="ov_read_float.html">ov_read_float</a></td> 70 <td>This function decodes to floats instead of integer samples.</td> 71 </tr> 72 <tr valign=top> 73 <td><a href="ov_read_filter.html">ov_read_filter</a></td> 74 <td>This function works like <a href="ov_read.html">ov_read</a>, but passes the PCM data through the provided filter before converting to integer sample data.</td> 75 </tr> 76 </table> 77 78 <br><br> 79 <hr noshade> 80 <table border=0 width=100%> 81 <tr valign=top> 82 <td><p class=tiny>copyright © 2007 Xiph.org</p></td> 83 <td align=right><p class=tiny><a href="http://www.xiph.org/ogg/vorbis/">Ogg Vorbis</a></p></td> 84 </tr><tr> 85 <td><p class=tiny>Vorbisfile documentation</p></td> 86 <td align=right><p class=tiny>vorbisfile version 1.2.0 - 20070723</p></td> 87 </tr> 88 </table> 89 90 </body> 91 92 </html> 93
