# Context options

OGG/Vorbis tuning options
Option | Definition | Relevance | Default
--- | --- | --- | ---
pcm_mode | PCM byte encoding used. See constants below. | Read / Write | `OGGVORBIS_PCM_S16_LE`
rate | PCM Sampling rate. Measured in Hz. | Write only | `44100`
bitrate | Vorbis Average Bitrate Encoding / Variable Bitrate Encoding. Measured in bps (ABR) or Quality level (VBR: 0.0 to 1.0). 128000 ABR is rough equal to 0.4 VBR. | Write only | `128000`
channels | Number of PCM channels. 1 == Mono, 2 == Stereo. | Write only | `2`
serialno | Serial Number of stream within file. Must be unique within file. Because of the potential to select a duplicate serial number within a chained file, make efforts to manually assign unique numbers when encoding. | Write only | Random
comments | Associative array of file comments. Will be translated to strtoupper($name) . "=$value". Note: This context option is not available in oggvorbis-0.1 | Write only | array('ENCODER' => 'PHP/OggVorbis, http://pear.php.net/oggvorbis')