Ogg is a free, open standard container format maintained by the Xiph.Org Foundation. The creators of the Ogg format claim that it is unrestricted by software patents and is designed to provide for efficient streaming and manipulation of high quality digital multimedia.
In the Ogg multimedia framework, Theora provides a lossy video layer, while the music-oriented Vorbis codec most commonly acts as the audio layer. The human speech compression codec Speex, lossless audio compression codec FLAC, and OggPCM may also act as audio layers.
The term ‘Ogg’ is commonly used to refer to audio file format Ogg Vorbis, that is, Vorbis-encoded audio in the Ogg container. Previously, the .ogg file extension was used for any content distributed within Ogg, but as of 2007, the Xiph.Org Foundation requests that .ogg be used only for Vorbis due to backward compatibility concerns. The Xiph.Org Foundation decided to create a new set of file extensions and media types to describe different types of content such as .oga for audio only files, .ogv for video with or without sound (including Theora), and .ogx for applications.
The current version of the Xiph.Org Foundation's reference implementation, released on June 23, 2009, is libogg 1.1.4. Another version, libogg2, has been in development, but is awaiting a rewrite as of 2008[3]. Both software libraries are free software, released under the new BSD license.
Because the format is free, and its reference implementation is non-copylefted, Ogg's various codecs have been incorporated into a number of different free and proprietary media players, both commercial and non-commercial, as well as portable media players and GPS receivers from different manufacturers.
The Ogg bitstream format, spearheaded by the Xiph.Org Foundation, has been created as the framework of a larger initiative aimed at developing a set of components for the coding and decoding of multimedia content which are available free of charge and are freely re-implementable in software.
The format consists of chunks of data each called an Ogg Page. Each page begins with the "OggS" string to identify the file as Ogg format.
A serial number and page number in the page header identifies each page as part of a series of pages making up a bitstream. Multiple bitstreams may be multiplexed in the file where pages from each bitstream are ordered by the seek time of the contained data. Bitstreams may also be appended to existing files, a process known as chaining, to cause the bitstreams to be decoded in sequence.
