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# CVI. oggvorbis

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The OGG/Vorbis file format, as defined by http://www.vorbis.com/, is a scheme for compressing audio streams by multiple factors with a minimum of quality loss. This extension adds Ogg Vorbis support to PHP's URL Wrappers. When used in read mode, compressed OGG/Vorbis data is expanded to raw PCM audio in one of six PCM encoding formats listed below.

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This extension requires PHP >= 4.3.0, libogg >= 1.0, and libvorbis >= 1.0.

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oggvorbis is installed through the usual PECL package installation process.

-     $ pear install oggvorbis

- Copy the resulting oggvorbis.so to an appropriate location and add extension=oggvorbis.so to your `php.ini` file or load it dynamically in your PHP script using dl('oggvorbis.so');

# Context options

表格 1. 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')`

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表格 2. OGG/Vorbis supports PCM encodings in the following formats

Constant | Definition
--- | ---
`OGGVORBIS_PCM_U8` | Unsigned 8-bit PCM.
`OGGVORBIS_PCM_S8` | Signed 8-bit PCM.
`OGGVORBIS_PCM_U16_LE` | Unsigned 16-bit PCM. Little Endian byte order.
`OGGVORBIS_PCM_U16_BE` | Unsigned 16-bit PCM. Big Endian byte order.
`OGGVORBIS_PCM_S16_LE` | Signed 16-bit PCM. Little Endian byte order.
`OGGVORBIS_PCM_S16_BE` | Signed 16-bit PCM. Big Endian byte order.

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