Ogg Theora
The Ogg Theora codec is a video codec developed by the Xiph.Org association, based on the ON2 technology of the VP3 codec. According to Theora's objective, Ogg Theora has comparable characteristics to video under MPEG-4, Xvid or DivX, and is similar to other video compressions that work with low bitrates, RealVideo or WindowsMedia Video(WMV).
While VP3 is a patented technology that must be licensed, the Theora based on it can be used by anyone.
Ogg Theora works with lossy compression and can be used for movie distribution and online video. It can compress video in the smallest format up to high-definition video, and at comparatively low bit rates. The compressed video format can be stored in a suitable container, such as an Ogg container. It is regularly combined with Vorbis audio. The format created from the Ogg container, Theora video, and Vorbis audio can be used royalty-free as a multimedia format. In contrast, other multimedia formats such as MPEG-4 video or MP3 are patented and subject to licensing and are used commercially.
Ogg Theora is used in HypertextMarkup Language (HTML5) for video display, Ogg Vorbis for audio playback. In addition, Firefox 3.5 supports this format, as does Opera 9.6. Like all other image and video compressions, Theora uses color subsampling. It uses a compression technique that works block by block and converts 8x8 pixel blocks via a DCT transformation, comparable to MPEG in its various versions.