Ogg (video)

Ogg is an open standard for a free container format for digital multimedia, unrestricted by software patents and designed for efficient streaming and manipulation. Ogg is maintained by the Xiph.Org Foundation.

The name ‘Ogg' refers to the file format which can multiplex a number of separate independent free and open source codecs for audio, video, text (such as subtitles), and metadata. The term ‘Ogg' is often used to refer to audio file format Ogg Vorbis, that is, Vorbis-encoded audio in the Ogg container. Other prominent Xiph codecs that are often encapsulated in Ogg are the video codec Theora, and the human speech audio compression format Speex.

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 backwards-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, .ogv for video (including Theora), and .ogx for applications.

The current version of the Xiph.Org Foundation's reference implementation, released on 27 November 2005, is libogg 1.1.3. Another version, libogg2, is also available from the Xiph.Org Foundation's SVN repositories. Both software libraries are free software, released under the new BSD license.

Because the format is free, 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.

Ogg is only a container format. The actual audio or video encoded by a codec will be stored inside an Ogg container. Ogg containers may contain streams encoded with multiple codecs, for example, an audio video file may contain data encoded by both an audio codec and a video codec.

Being a Container format, Ogg can embed audio and video in various formats (such as MPEG-4, Dirac, MP3 and others) but usually Ogg is used with the following video codecs:

• Theora: based upon On2's VP3, it is targeted at competing with MPEG-4 video (for example, encoded with DivX or Xvid), RealVideo, or Windows Media Video.
• Tarkin: an experimental codec utilizing discrete wavelet transforms in the three dimensions of width, height, and time. It has been put on hold since February 2000, with Theora becoming the main focus for video encoding.
• Dirac: an experimental codec developed by the BBC as the basis of a new codec for the transmission of video over the Internet. The Schrödinger project aims to provide portable libraries, written in C, that implement the Dirac codec. It also allows to embed Dirac inside the Ogg container format.
• OggUVS: a draft codec for storing uncompressed video.