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Theora is a free lossy video compression format.. It was developed by the Xiph.Org Foundation and distributed without licensing fees alongside their other free and open media projects, including the Vorbis audio format and the Ogg container.
The libtheora video codec is the reference implementation of the Theora video compression format developed by the Xiph.Org Foundation.
Theora was derived from the formerly proprietary VP3 codec, released into the public domain by On2 Technologies. It is broadly comparable in design and bitrate efficiency to MPEG-4 Part 2, early versions of Windows Media Video, and RealVideo while it lacked some of the features present in some of these other codecs. It is comparable in open standards philosophy to the BBC's Dirac codec.
Theora was named after Theora Jones, Edison Carter's Controller on the Max Headroom television program.
Theora video streams can be stored in any suitable container format, but they are most commonly found in the Ogg container with Vorbis or FLAC audio streams. This combination provided a completely open, royalty-free multimedia format. It can also be used with the Matroska container.
The Theora video-compression format is compatible with the VP3 video-compression format, which consisted of a backward-compatible superset.Xiph.org FAQ – Theora and VP3. Retrieved 2 September 2009 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 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 License-style license.Linux.com (23 June 2002) Ogg Vorbis, VP3 combining forces to create Open Source multimedia package, Retrieved on 2009-08-16InternetNews.com (24 June 2002) On2 Throws More Open-Source at MPEG-4, Retrieved on 16 August 2009 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.Xiph.org libtheora license (Subversion – Trunk), Retrieved on 16 August 2009Xiph.org VP32 codec license (Subversion – Trunk), Retrieved on 16 August 2009 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.The Free Library (1 August 2002) On2 Signs Pact With Xiph.org to Develop/Support VP3, Retrieved on 16 August 2009 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.
There is no formal specification for VP3's bitstream format beyond the VP3 source code published by On2 Technologies. In 2003, Mike Melanson created an incomplete description of the VP3 bitstream format and decoding process at a higher level than source code, with some help from On2 and Xiph.Org Foundation. The Theora specification adopted some portions of this VP3 description.
A successor to Theora, Daala, was later merged into AV1.
The Theora reference implementation libtheora spent several years in alpha and beta status. The first alpha version was released on 25 September 2002 and the first beta version was released on 22 September 2007. The first stable release of libtheora was made in November 2008. Work then focused on improving the codec's performance in the "Thusnelda" branch, which was released as version 1.1 in September 2009 as the second stable libtheora release. This release brought some technical improvements and new features, such as the new rate control module and the two-pass rate control.
The codename for the next version of libtheora was Ptalarbvorm.
Theora was well established as a video format in open-source applications, and became the format used for Wikipedia's video content before replaced by VP9. However, the proposed adoption of Theora as part of the baseline video support in HTML5 resulted in controversy.
The differences in quality, bitrate and file size between a YouTube H.264 video and a transcoded Ogg video file are very small.
| Unix-like | OS X | Windows | |
| | style="text-align: left;" A command-line program that transcodes video by decoding with FFmpeg and reencoding with libtheora to encode it | |||
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| | style="text-align: left;" "Video DJing" software that can encode to and stream Theora | ? | ||
| | style="text-align: left;" The video editor supplied with KDE | ? | ? | |
| | style="text-align: left;" The video editor supplied with GNOME | ? | ? | |
| | style="text-align: left;" Video editing software for Linux. Can edit, encode and stream theora. | ? | ||
| | style="text-align: left;" Can output to Theora only with the Matroska container | |||
| | style="text-align: left;" Records the screen to Ogg Theora with optional Vorbis audio | ? | ? |
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 licenses.
Also, several media frameworks have support for Theora.
| Unix-like | OS X | Windows | |
| | style="text-align: left;" Video editing software for Linux. Can edit, encode and stream theora. | ? | ||
| | style="text-align: left;" The KDE video editor. | ? | ? | |
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| | style="text-align: left;" The GNOME video editor. | ? | ? | |
| | style="text-align: left;" CVS versions of the Cinelerra non-linear video editing system support Theora, as of August 2005. | ? | ||
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| | style="text-align: left;" Can stream ogg/theora/vorbis in realtime to a file or fifo. | ? | ||
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