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1 <html>
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2
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3 <head>
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4 <title>Vorbisfile - function - ov_read</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 1.3.2 - 20101101</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_read()</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>
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21 This is the main function used to decode a Vorbis file within a
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22 loop. It returns up to the specified number of bytes of decoded PCM audio
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23 in the requested endianness, signedness, and word size. If the audio is
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24 multichannel, the channels are interleaved in the output buffer.
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25 If the passed in buffer is large, <tt>ov_read()</tt> will not fill
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26 it; the passed in buffer size is treated as a <em>limit</em> and
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27 not a request.
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28
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29 <p>The output channels are in stream order and not remapped. Vorbis I
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30 defines channel order as follows:
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31
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32 <ul>
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33 <li>one channel - the stream is monophonic
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34 <li>two channels - the stream is stereo. channel order: left, right
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35 <li>three channels - the stream is a 1d-surround encoding. channel order: left,
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36 center, right
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37 <li>four channels - the stream is quadraphonic surround. channel order: front left,
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38 front right, rear left, rear right
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39 <li>five channels - the stream is five-channel surround. channel order: front left,
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40 center, front right, rear left, rear right
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41 <li>six channels - the stream is 5.1 surround. channel order: front left, center,
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42 front right, rear left, rear right, LFE
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43 <li>seven channels - the stream is 6.1 surround. channel order: front left, center,
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44 front right, side left, side right, rear center, LFE
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45 <li>eight channels - the stream is 7.1 surround. channel order: front left, center,
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46 front right, side left, side right, rear left, rear right,
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47 LFE
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48 <li>greater than eight channels - channel use and order is undefined
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49 </ul>
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50
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51 <p>Note that up to this point, the Vorbisfile API could more or less hide the
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52 multiple logical bitstream nature of chaining from the toplevel
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53 application if the toplevel application didn't particularly care.
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54 However, when reading audio back, the application must be aware
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55 that multiple bitstream sections do not necessarily use the same
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56 number of channels or sampling rate. <p> <tt>ov_read()</tt> passes
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57 back the index of the sequential logical bitstream currently being
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58 decoded (in <tt>*bitstream</tt>) along with the PCM data in order
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59 that the toplevel application can handle channel and/or sample
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60 rate changes. This number will be incremented at chaining
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61 boundaries even for non-seekable streams. For seekable streams, it
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62 represents the actual chaining index within the physical bitstream.
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63 <p>
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64
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65 <br><br>
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66 <table border=0 color=black cellspacing=0 cellpadding=7>
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67 <tr bgcolor=#cccccc>
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68 <td>
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69 <pre><b>
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70 long ov_read(<a href="OggVorbis_File.html">OggVorbis_File</a> *vf, char *buffer, int length, int bigendianp, int word, int sgned, int *bitstream);
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71 </b></pre>
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72 </td>
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73 </tr>
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74 </table>
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75
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76 <h3>Parameters</h3>
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77 <dl>
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78 <dt><i>vf</i></dt>
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79 <dd>A pointer to the OggVorbis_File structure--this is used for ALL the externally visible libvorbisfile
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80 functions.</dd>
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81 <dt><i>buffer</i></dt>
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82 <dd>A pointer to an output buffer. The decoded output is inserted into this buffer.</dd>
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83 <dt><i>length</i></dt>
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84 <dd>Number of bytes to be read into the buffer. Should be the same size as the buffer. A typical value is 4096.</dd>
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85 <dt><i>bigendianp</i></dt>
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86 <dd>Specifies big or little endian byte packing. 0 for little endian, 1 for b
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87 ig endian. Typical value is 0.</dd>
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88 <dt><i>word</i></dt>
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89 <dd>Specifies word size. Possible arguments are 1 for 8-bit samples, or 2 or
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90 16-bit samples. Typical value is 2.</dd>
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91 <dt><i>sgned</i></dt>
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92 <dd>Signed or unsigned data. 0 for unsigned, 1 for signed. Typically 1.</dd>
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93 <dt><i>bitstream</i></dt>
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94 <dd>A pointer to the number of the current logical bitstream.</dd>
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95 </dl>
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96
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97
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98 <h3>Return Values</h3>
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99 <blockquote>
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100 <dl>
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101 <dt>OV_HOLE</dt>
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102 <dd>indicates there was an interruption in the data.
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103 <br>(one of: garbage between pages, loss of sync followed by
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104 recapture, or a corrupt page)</dd>
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105 <dt>OV_EBADLINK</dt>
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106 <dd>indicates that an invalid stream section was supplied to
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107 libvorbisfile, or the requested link is corrupt.</dd>
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108 <dt>OV_EINVAL</dt>
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109 <dd>indicates the initial file headers couldn't be read or
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110 are corrupt, or that the initial open call for <i>vf</i>
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111 failed.</dd>
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112 <dt>0</dt>
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113 <dd>indicates EOF</dd>
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114 <dt><i>n</i></dt>
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115 <dd>indicates actual number of bytes read. <tt>ov_read()</tt> will
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116 decode at most one vorbis packet per invocation, so the value
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117 returned will generally be less than <tt>length</tt>.
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118 </dl>
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119 </blockquote>
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120
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121 <h3>Notes</h3>
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122 <p><b>Typical usage:</b>
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123 <blockquote>
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124 <tt>bytes_read = ov_read(&vf,
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125 buffer, 4096,0,2,1,&current_section)</tt>
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126 </blockquote>
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127
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128 This reads up to 4096 bytes into a buffer, with signed 16-bit
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129 little-endian samples.
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130 </p>
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131
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132
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133
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134 <br><br>
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135 <hr noshade>
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136 <table border=0 width=100%>
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137 <tr valign=top>
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138 <td><p class=tiny>copyright © 2000-2010 Xiph.Org</p></td>
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139 <td align=right><p class=tiny><a href="http://www.xiph.org/ogg/vorbis/">Ogg Vorbis</a></p></td>
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140 </tr><tr>
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141 <td><p class=tiny>Vorbisfile documentation</p></td>
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142 <td align=right><p class=tiny>vorbisfile version 1.3.2 - 20101101</p></td>
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143 </tr>
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144 </table>
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145
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146 </body>
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147
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148 </html>
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