The Theora video-compression format is compatible with the VP3 video-compression format, which consisted of a backward-compatible superset. Theora is a superset of VP3, and VP3 streams (with some minor syntactic modifications) can be converted into Theora streams without recompression (but not vice versa). VP3 video compression can be decoded using Theora implementations, but Theora video compression usually cannot be decoded using old VP3 implementations.
In August 2001, On2 Technologies announced that they would release an open source version of their VP3.2 video compression algorithm. In September 2001, On2 Technologies published the source code of the VP3.2 codec under the VP3.2 Public License 0.1, a custom open-source license. The license only granted the right to modify the source code if the resultant larger work continued to support playback of VP3.2 data.
In March 2002, On2 responded to the public's reception by relicensing the VP3 codec under the GNU Lesser General Public License. In June 2002, On2 donated VP3 to the Xiph.Org Foundation and offered it under the Ogg Vorbis BSD-style license. On2 also made an irrevocable, royalty-free license grant for any patent claims it might have over the software and any derivatives, allowing anyone to use any VP3-derived codec for any purpose. In August 2002, On2 entered into an agreement with the Xiph.Org Foundation to make VP3 the basis of a new, free video codec, called Theora. On2 declared Theora to be VP3's successor. On 3 October 2002, On2 and Xiph announced the completion and availability of the initial alpha code release of libtheora, Theora's reference implementation.
In October 2023, Google announced intent to remove Theora support from Chromium (finalizing removal by Google Chrome 123), with Firefox following suit. Google developers claimed that despite lack of adoption, Theora made a case for open and royalty-free codecs like AV1.[better source needed]
Evaluations of the VP3
and early Theora encoders
found that their subjective visual quality was inferior to that of contemporary video codecs. The performance characteristics of the Theora 1.0 reference implementation are dominated mostly by implementation problems inherited from the original VP3 code base. Work that lead up to the 1.1 stable release focused on improving on or eliminating these. A May 2009 review of this work by Xiph developer Chris Montgomery claimed a considerable improvement in quality, both subjectively and as measured by PSNR, by improving the forward DCT and quantisation matrices. More recently however,[when?] Xiph developers compared the 1.1 Theora encoder to YouTube's H.264 and H.263+ encoders, in response to concerns raised in 2009 about Theora's inferior performance by Chris DiBona, a Google employee. They found the results from Theora to be nearly the same as YouTube's H.264 output, and much better than the H.263+ output.
The differences in quality, bitrate and file size between a YouTube H.264 video and a transcoded Ogg video file are very small.
The libtheora library contains the reference implementation of the Theora specification for encoding and decoding. libtheora was developed by the Xiph.Org Foundation. The library was released under the terms of a BSD-style license.
Also, several media frameworks have support for Theora.
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