| [15] | 1 | <html> |
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| 2 | |
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| 3 | <head> |
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| 4 | <title>libogg - Decoding</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>libogg documentation</p></td> |
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| 12 | <td align=right><p class=tiny>libogg release 1.0 - 20000615</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>Decoding</h1> |
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| 17 | <p>Libogg contains a set of functions used in the decoding process. |
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| 18 | <p> |
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| 19 | All the <b>libogg</b> specific functions are declared in "ogg/ogg.h". |
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| 20 | <p> |
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| 21 | <p>Decoding is based around the ogg synchronization layer. The <a href="ogg_sync_state.html">ogg_sync_state</a> struct coordinates between incoming data and the decoder. We read data into the synchronization layer, submit the data to the stream, and output raw packets to the decoder. |
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| 22 | <p>Decoding through the Ogg layer follows a specific logical sequence. A read loop follows these logical steps: |
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| 23 | <ul> |
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| 24 | <li>Expose a buffer using <a href="ogg_sync_buffer.html">ogg_sync_buffer()</a>. |
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| 25 | <li>Read data into the buffer, using fread() or a similar function. |
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| 26 | <li>Call <a href="ogg_sync_wrote.html">ogg_sync_wrote()</a> to tell the synchronization layer how many bytes you wrote into the buffer. |
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| 27 | <li>Write out the data using <a href="ogg_sync_pageout.html">ogg_sync_pageout</a>. |
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| 28 | <li>Submit the completed page to the streaming layer with <a href="ogg_stream_pagein.html">ogg_stream_pagein</a>. |
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| 29 | <li>Output a packet of data to the codec-specific decoding layer using <a href="ogg_stream_packetout.html">ogg_stream_packetout</a>. |
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| 30 | </ul> |
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| 31 | <p>In practice, streams are more complex, and Ogg also must handle headers, incomplete or dropped pages, and other errors in input. |
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| 32 | <br><br> |
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| 33 | |
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| 34 | <table border=1 color=black width=50% cellspacing=0 cellpadding=7> |
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| 35 | <tr bgcolor=#cccccc> |
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| 36 | <td><b>function</b></td> |
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| 37 | <td><b>purpose</b></td> |
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| 38 | </tr> |
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| 39 | <tr valign=top> |
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| 40 | <td><a href="ogg_sync_init.html">ogg_sync_init</a></td> |
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| 41 | <td>Initializes an Ogg bitstream.</td> |
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| 42 | </tr> |
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| 43 | <tr valign=top> |
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| 44 | <td><a href="ogg_sync_clear.html">ogg_sync_clear</a></td> |
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| 45 | <td>Clears the status information from the synchronization struct.<td> |
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| 46 | </tr> |
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| 47 | <tr valign=top> |
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| 48 | <td><a href="ogg_sync_reset.html">ogg_sync_reset</a></td> |
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| 49 | <td>Resets the synchronization status to initial values.</td> |
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| 50 | </tr> |
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| 51 | <tr valign=top> |
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| 52 | <td><a href="ogg_sync_destroy.html">ogg_sync_destroy</a></td> |
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| 53 | <td>Frees the synchronization struct.</td> |
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| 54 | </tr> |
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| 55 | <tr valign=top> |
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| 56 | <td><a href="ogg_sync_buffer.html">ogg_sync_buffer</a></td> |
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| 57 | <td>Exposes a buffer from the synchronization layer in order to read data.</td> |
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| 58 | </tr> |
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| 59 | <tr valign=top> |
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| 60 | <td><a href="ogg_sync_wrote.html">ogg_sync_wrote</a></td> |
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| 61 | <td>Tells the synchronization layer how many bytes were written into the buffer.</td> |
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| 62 | </tr> |
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| 63 | <tr valign=top> |
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| 64 | <td><a href="ogg_sync_pageseek.html">ogg_sync_pageseek</a></td> |
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| 65 | <td>Finds the borders of pages and resynchronizes the stream.</td> |
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| 66 | </tr> |
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| 67 | <tr valign=top> |
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| 68 | <td><a href="ogg_sync_pageout.html">ogg_sync_pageout</a></td> |
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| 69 | <td>Outputs a page from the synchronization layer.</td> |
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| 70 | </tr> |
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| 71 | <tr valign=top> |
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| 72 | <td><a href="ogg_stream_pagein.html">ogg_stream_pagein</a></td> |
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| 73 | <td>Submits a complete page to the stream layer.</td> |
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| 74 | </tr> |
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| 75 | <tr valign=top> |
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| 76 | <td><a href="ogg_stream_packetout.html">ogg_stream_packetout</a></td> |
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| 77 | <td>Outputs a packet to the codec-specific decoding engine.</td> |
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| 78 | </tr> |
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| 79 | <tr valign=top> |
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| 80 | <td><a href="ogg_stream_packetpeek.html">ogg_stream_packetpeek</a></td> |
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| 81 | <td>Provides access to the next packet in the bitstream without |
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| 82 | advancing decoding.</td> |
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| 83 | </tr> |
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| 84 | </table> |
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| 85 | |
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| 86 | <br><br> |
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| 87 | <hr noshade> |
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| 88 | <table border=0 width=100%> |
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| 89 | <tr valign=top> |
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| 90 | <td><p class=tiny>copyright © 2000 xiph.org</p></td> |
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| 91 | <td align=right><p class=tiny><a href="http://www.xiph.org/ogg/vorbis/">Ogg Vorbis</a><br><a href="mailto:team@xiph.org">team@xiph.org</a></p></td> |
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| 92 | </tr><tr> |
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| 93 | <td><p class=tiny>libogg documentation</p></td> |
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| 94 | <td align=right><p class=tiny>libogg release 1.0 - 20000615</p></td> |
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| 95 | </tr> |
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| 96 | </table> |
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| 97 | |
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| 98 | </body> |
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| 99 | |
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| 100 | </html> |
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