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Theora

From Wikipedia, the free encyclopedia
For the genus of clams, seeTheora (bivalve).

Theora
Filename extension
.ogv,.ogg
Internet media type
video/ogg
Developed byXiph.org
Initial release1 June 2004(2004-06-01)[1]
Latest release
Theora I
16 March 2011[2]
Type of formatVideo coding format
Contained byOgg,Matroska
Extended fromVP3
StandardSpecification
Open format?Yes[3]
Free format?Yes[4]
Websitetheora.org
libtheora
Developer(s)Xiph.org
Initial release3 November 2008(2008-11-03)(1.0)
Stable release
1.1.1 / 1 October 2009;14 years ago(2009-10-01)[5]
Preview release
1.2.0 Alpha 1 / 24 September 2010;14 years ago(2010-09-24)[6]
Written inC
Operating systemUnix-like(inclLinux,Mac OS X),Windows
TypeVideo codec,reference implementation
License3-clause BSD
Websitewww.theora.org

Theorais afreelossyvideo compression format.[7]It was developed by theXiph.Org Foundationand distributed without licensing fees alongside their other free and open media projects, including theVorbisaudio format and theOggcontainer.

Thelibtheoravideo codecis thereference implementationof the Theora video compression format developed by the Xiph.Org Foundation.[8][9]

Theora was derived from the formerlyproprietaryVP3codec, released into thepublic domainbyOn2 Technologies.It is broadly comparable in design and bitrate efficiency toMPEG-4 Part 2,early versions ofWindows Media Video,andRealVideowhile it lacked some of the features present in some of these other codecs. It is comparable in open standards philosophy to theBBC'sDiraccodec.

Theora was named afterTheora Jones,Edison Carter's Controller on theMax Headroomtelevision program.[10]

Technical details

[edit]

Theora is avariable-bitrate,DCT-based video compression scheme. Like most common video codecs, Theora usedchroma subsampling,block-based motion compensation and an 8-by-8 DCT block. Pixels are grouped into various structures, namely blocks, super blocks, andmacroblocks.Theora supports intra-coded frames ( "keyframes" ) and forward-predictive frames, but notbi-predictive frameswhich are found inH.264andVC-1.Theora also does not supportinterlacing,or bit-depths larger than 8 bits per component.[2]

Theora video streams can be stored in any suitablecontainer format,but they are most commonly found in theOggcontainer withVorbisorFLACaudio streams. This combination provided a completely open, royalty-free multimedia format. It can also be used with theMatroskacontainer.[11]

The Theora video-compression format is compatible with the VP3 video-compression format, which consisted of a backward-compatible superset.[12][13]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).[13]VP3 video compression can be decoded using Theora implementations, but Theora video compression usually cannot be decoded using old VP3 implementations.

History

[edit]
See also:VP3

Theora's predecessorOn2 TrueMotion VP3was originally aproprietaryand patent-encumberedvideo codecdeveloped byOn2 Technologies.VP3.1 was introduced in May 2000[14]and followed three months later by the VP3.2 release,[15]which was the basis for Theora.

Move to free software

[edit]

In August 2001, On2 Technologies announced that they would release an open source version of their VP3.2 video compression algorithm.[16][17]In September 2001, On2 Technologies published thesource codeof 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 resultant 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 theGNU Lesser General Public License.[22]In June 2002, On2 donated VP3 to the Xiph.Org Foundation and offered it under the Ogg VorbisBSD-style license.[23][24][25][26]On2 also made an irrevocable,royalty-freelicense 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.[citation needed]On 3 October 2002, On2 and Xiph announced the completion and availability of the initial alpha code release oflibtheora,Theora's reference implementation.[29]

There is no formal specification for VP3'sbitstream formatbeyond 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 intoAV1.[31]

Theora I specification

[edit]
Example of a Theora video used onWikipedia,showing aPolikarpov I-15biplane at an aerobatic display.

The Theora I bitstream format wasfrozenin 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. TheTheora I Specificationwas completely published in 2004.[33]Any later changes in the specification are minor updates.

The Theora reference implementation libtheora spent several years inalphaand 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 thetwo-pass rate control.

The codename for the next version of libtheora wasPtalarbvorm.[38]

Theora was well established as a video format inopen-source applications,and became the format used forWikipedia's video content before replaced byVP9.However, the proposed adoption of Theora as part of the baseline video support in HTML5resulted in controversy.[39]

Legacy

[edit]

In October 2023, Google announced intent to remove Theora support from Chromium (finalizing removal by Google Chrome 123),[40]with Firefox following suit. Google developers claimed that despite lack of adoption, Theora made a case for open and royalty-free codecs likeAV1.[41][better source needed]

Performance

[edit]

Encoding performance

[edit]

Evaluations of the VP3[42] and early Theora encoders[43][44][45] 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.[46]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 byPSNR,by improving the forwardDCTand quantisation matrices.[47]More recently however,[when?]Xiph developers compared the 1.1 Theora encoder toYouTube's H.264 andH.263+encoders, in response to concerns raised in 2009 about Theora's inferior performance byChris DiBona,aGoogleemployee.[48]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.[49][50]

The differences in quality, bitrate and file size between a YouTube H.264 video and a transcoded Ogg video file are very small.[51]

Playback performance

[edit]

There was anopen-sourceVHDLcode base for a hardware Theora decoder in development.[52][needs update]It began as a 2006GoogleSummer of Codeproject, and it has been developed on both theNios IIandLEONprocessors.[53]However, there are currently no Theora decoder chips in production, andportable media players,smartphonesand similar devices with limited computing power rely on such chips to provide efficient playback.

Playback

[edit]

Web browsers

[edit]
Main article:Use of Ogg formats in HTML5

As originally recommended byHTML 5,these browsers support Theora when embedded by thevideoelement:

Supporting media frameworks

[edit]

Supporting applications

[edit]

Encoding

[edit]

There are several third-party programs that support encoding through libtheora:

Name Description Operating Systems Supported
Unix-like OS X Windows
ffmpeg2theora[71]
 A command-line program that transcodes video by decoding withFFmpegand reencoding with libtheora to encode it Yes Yes Yes
VLC
 Can transcode to single-pass Theora 1.0 and optionally stream it Yes Yes Yes
FreeJ
 "Video DJing" software that can encode to and stream Theora Yes Yes ?
Kdenlive
 The video editor supplied withKDE Yes ? ?
Pitivi
 The video editor supplied withGNOME Yes ? ?
LiVES
 Video editing software for Linux. Can edit, encode and stream theora. Yes Yes ?
HandBrake
 Can output to Theora only with theMatroskacontainer Yes Yes Yes
RecordMyDesktop
 Records the screen to Ogg Theora with optional Vorbis audio Yes ? ?

The libtheora library contains the reference implementation of the Theora specification for encoding and decoding. libtheora was developed by theXiph.Org Foundation.The library was released under the terms of aBSD-style license.

Also, several media frameworks have support for Theora.

  • The open-sourceffdshowaudio/video decoder is capable of encoding Theora videos using itsVideo for Windows(VFW) multi-codec interface within popular AVI editing programs.[72][73][74]It supports both encoding and decoding Theora video streams and uses Theora's alpha 4 libraries. However, many of the more refined features of Theora are not available to the user in ffdshow's interface.
  • TheGStreamerframework has support for parsing raw Theora streams, encoding and decoding raw Theora streams to/from YUV video[75][76]

Editing

[edit]
Name Description Operating Systems Supported
Unix-like OS X Windows
LiVES
 Video editing software for Linux. Can edit, encode and stream theora. Yes Yes ?
Kdenlive
 TheKDEvideo editor. Yes ? ?
OpenShot
 Yes ? ?
Pitivi
 TheGNOMEvideo editor. Yes ? ?
Cinelerra
 CVSversions of theCinelerranon-linear video editing systemsupport Theora, as of August 2005. Yes Yes ?
oggz-tools byXiph.org
 Command line programs to examine and edit Ogg files. Yes ? Yes
Ogg Video Tools by yornstreamnik
 Tools to resize, cut, split, join, and others[77] Yes Yes Yes
AVS Video Editor
 ? ? Yes

Streaming

[edit]

The following streaming media servers are capable of streaming Theora video:

Name Description Operating Systems Supported
Unix-like OS X Windows
VLC
 Yes Yes Yes
Icecast
 Yes ? Yes
LiVES
 Can stream ogg/theora/vorbis in realtime to a file or fifo. Yes Yes ?

Makers

[edit]

Elphelis the main maker of cameras that record in theora.

See also

[edit]

References

[edit]
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  2. ^abcd"Theora Specification"(PDF).Xiph.Org Foundation. 16 March 2011.Retrieved31 January2012.
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