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Theora is a video codec being developed by the Foundation as part of their Ogg project. Based upon On2's VP3 codec, and christened by On2 as the successor in VP3's lineage, Theora is targeted at competing with MPEG-4 (e.g., XviD and DivX), RealVideo, Windows Media Video, and similar lower-bitrate video compression schemes.

Theora is still in developmental stages with having made two alpha releases thus far (Alpha One was released on September 25, 2002; Alpha Two was released half on December 16 and half on December 27, 2002). One last milestone release is expected, with the target date for the final production release being sometime in June of 2003. Theora is released under the terms of a BSD-style license.

While VP3 is patented technology, On2 has irrevocably given royalty-free license of the VP3 patents to all of humanity, enabling the public to utilize Theora and other VP3-derived codecs for any imaginable purpose.

In the Ogg multimedia framework, Theora provides a video layer, while Vorbis acts as the audio layer.


;September 6, 2001 : On2 releases the source code to their libraries for VP3 under the terms of the VP3.2 Public License.

;March 27, 2002 : On2's founder and CTO, Dan Miller, sends an email to vorbis-dev announcing On2's interest in collaborating with the Foundation and relicensing VP3 under the terms of the LGPL.

;June 24, 2002 : On2 and the Foundation announce their alliance to develop Ogg Theora: the integration of VP3 with the Ogg framework and Vorbis. See also On2's press release.

;September 25, 2002 : Theora Alpha One is released. See also On2's press release.

;December 16 and 27, 2002 : Theora Alpha Two is released in two stages.

;May 18, 2003 : Published VP3 legacy codec binaries.

;June 9, 2003 : Theora reference implementation Alpha Two is released.

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