Theora

In August 2001, On2 Technologies announced that they would be releasing an open source version of their VP3.2 video compression algorithm.[16][17] In September 2001, On2 Technologies published the source code of the VP3.2 codec under the VP3.2 Public License 0.1,[18] a custom open-source license.[19][20] The license only granted the right to modify the source code if the resulting larger work continued to support playback of VP3.2 data.[18][21]

In March 2002, On2 responded to the public's reception by relicensing the VP3 codec under the GNU Lesser General Public License.[22] In June 2002, On2 donated VP3 to the Xiph.Org Foundation and offered it under the Ogg Vorbis BSD-style license.[23][24][25][26] On2 also made an irrevocable, royalty-free license grant for any patent claims it might have over the software and any derivatives,[2] allowing anyone to use any VP3-derived codec for any purpose.[12][27] 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.[28] 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.[29]

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.[2][30]

A successor to Theora, Daala, was later merged into AV1.[31]

The Theora I bitstream format was frozen in June 2004 after the libtheora 1.0alpha3 release.[1] Videos encoded with any version of the libtheora since the alpha3 will be compatible with any future player.[1][32] This is also true for videos encoded with any implementation of the Theora I specification since the format freeze. The Theora I Specification was completely published in 2004.[33] Any later changes in the specification are minor updates.

The Theora reference implementation libtheora spent several years in alpha and beta status.[32] The first alpha version was released on 25 September 2002 and the first beta version was released on 22 September 2007.[34] The first stable release of libtheora was made in November 2008.[35][36] 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.[32][37] 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 is Ptalarbvorm.[38]

Theora is well established as a video format in open-source applications, and became the format used for Wikipedia's video content before being mostly replaced by VP9. However, the proposed adoption of Theora as part of the baseline video support in HTML5 resulted in controversy.[39]

Evaluations of the VP3[40] and early Theora encoders[41][42][43] found that their subjective visual quality was inferior to that of contemporary video codecs. More recently however, 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.[44] 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.[45][46]

The performance characteristics of the Theora 1.0 reference implementation are dominated mostly by implementation problems inherited from the original VP3 code base.[47] Work leading up to the 1.1 stable release was focused on improving on or eliminating these. A May 2009 review of this work claimed a considerable improvement in quality, both subjectively and as measured by PSNR, just by improving the forward DCT and quantisation matrices.[48] A flaw in the version of FFmpeg used in the test initially led to incorrect reports of Theora PSNR surpassing that of H.264. The differences in quality, bitrate and file size between a YouTube H.264 video and a transcoded Ogg video file are very small.[49] Further work on adaptive quantization, as well as overall detailed subjective tuning of the codec, is still to come.

There is an open-source VHDL code base for a hardware Theora decoder in development.[50] It began as a 2006 Google Summer of Code project, and it has been developed on both the Nios II and LEON processors.[51] However, there are currently no Theora decoder chips in production, and portable media players, smartphones and similar devices with limited computing power rely on such chips to provide efficient playback.

As originally recommended by HTML 5, these browsers support Theora when embedded by the video element:

• Mozilla Firefox 3.5 and later versions[52][53] including Firefox for mobile (Fennec).[54]
• Google Chrome as of version 3.0.182.2[55][56] including Chromium as of 14 July 2009.[57] Support for Theora is planned to be deprecated in version 120 and removed in version 123.[58]
• Tizen browser
• SeaMonkey as of version 2.0.[59]
• Konqueror 4.4.2[60][61]
• Opera as of version 10.50.[62][63] It was also supported in Opera 9.5 experimental video builds.[64][65]
• Web uses WebKitGTK+ as its rendering engine. As WebKitGTK+ uses GStreamer to implement the HTML5 media player, and all the formats GStreamer supports (including Theora) are available in browser.
• Midori is another example of a browser that supports Theora by using WebKitGTK+.

• Annodex plugin via OggPlay[66]
• Cortado, a Java based applet
  • Itheora, a PHP wrapper for Cortado
• Mv Embed[67] HTML 5 video tag wrapper for numerous plugin types
• VLC media player browser plugin for IE or Firefox
• Microsoft Edge, via the Web Media Extensions add-on[68]

• DirectShow with use of OpenCodecs
• GStreamer supported via Theora or FFmpeg module, supports GStreamer based applications e.g. Totem and Songbird
• Phonon
• QuickTime (including but not limited to Safari) with use of Xiph QuickTime Components
• Silverlight Highgate media suite is going to bring an Open Source Theora/Vorbis implementation in Silverlight. It will enable installation-free support for HTML5 streaming video.[69]

• FFmpeg (own implementation)
• Helix Player
• Miro Media Player (formerly known as Democracy Player)
• MPlayer and front-ends
• Songbird, Totem, Moovida and all GStreamer-based players
• VLC (native support)
• xine and all libxine-based players like Kaffeine
• Dragon player and all Phonon-based players