CIII. oggvorbis

Introduction

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.

Requirements

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

Runtime Configuration

This extension has no configuration directives defined in php.ini.

Installation

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

Table 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')`

Predefined Constants

The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.

Table 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.

Table of Contents
Usage -- Examples on using the ogg:// wrapper.