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1 <html>
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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 1.3.0 - 20110804</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_check.html">ogg_sync_check</a></td>
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57 <td>Check for asynchronous errors.</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_buffer.html">ogg_sync_buffer</a></td>
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61 <td>Exposes a buffer from the synchronization layer in order to read data.</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_wrote.html">ogg_sync_wrote</a></td>
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65 <td>Tells the synchronization layer how many bytes were written into the buffer.</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_pageseek.html">ogg_sync_pageseek</a></td>
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69 <td>Finds the borders of pages and resynchronizes the stream.</td>
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70 </tr>
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71 <tr valign=top>
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72 <td><a href="ogg_sync_pageout.html">ogg_sync_pageout</a></td>
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73 <td>Outputs a page from the synchronization 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_pagein.html">ogg_stream_pagein</a></td>
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77 <td>Submits a complete page to the stream layer.</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_packetout.html">ogg_stream_packetout</a></td>
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81 <td>Outputs a packet to the codec-specific decoding engine.</td>
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82 </tr>
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83 <tr valign=top>
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84 <td><a href="ogg_stream_packetpeek.html">ogg_stream_packetpeek</a></td>
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85 <td>Provides access to the next packet in the bitstream without
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86 advancing decoding.</td>
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87 </tr>
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88 </table>
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89
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90 <br><br>
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91 <hr noshade>
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92 <table border=0 width=100%>
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93 <tr valign=top>
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94 <td><p class=tiny>copyright © 2000-2011 Xiph.Org</p></td>
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95 <td align=right><p class=tiny><a href="http://www.xiph.org/ogg/">Ogg Container Format</a></p></td>
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96 </tr><tr>
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97 <td><p class=tiny>libogg documentation</p></td>
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98 <td align=right><p class=tiny>libogg release 1.3.0 - 20110804</p></td>
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99 </tr>
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100 </table>
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101
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102 </body>
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103
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104 </html>
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