Theora

For the genus of clams, see Theora (genus).
Theora
Filename extension .ogv, .ogg
Internet media type video/ogg
Developed by Xiph.org
Initial release 1 June 2004 (2004-06-01)[1]
Latest release
Theora I
(16 March 2011[2])
Type of format Compressed video
Contained by Ogg, Matroska
Extended from VP3
Standard Specification
Open format? Yes[3]
Website theora.org
libtheora
Developer(s) Xiph.org
Initial release 3 November 2008 (2008-11-03) (1.0)
Stable release 1.1.1 / 1 October 2009 (2009-10-01)[4]
Preview release 1.2.0 Alpha 1 / 24 September 2010 (2010-09-24)[5]
Development status Inactive
Written in C
Operating system Unix-like (incl Linux, Mac OS X), Windows
Type Video codec, reference implementation
License 3-clause BSD
Website theora.org

Theora is a free lossy video compression format.[6] It is 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 being developed by the Xiph.Org Foundation.[7][8]

Theora is 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 lacking 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 is named after Theora Jones, Edison Carter's Controller on the Max Headroom television program.[9]

Technical details

Theora is a variable-bitrate, DCT-based video compression scheme. Like most common video codecs, Theora also uses chroma subsampling, block-based motion compensation and an 8-by-8 DCT block. Pixels are grouped into various structures, namely blocks, super blocks, and macroblocks. Theora supports intra-coded frames and forward-predictive frames, but not bi-predictive frames which are found in H.264 and VC-1. Theora also does not support interlacing, or bit-depths larger than 8 bits per component.[2]

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 provides a completely open, royalty-free multimedia format. It can also be used with the Matroska container.[10]

The Theora video-compression format is essentially compatible with the VP3 video-compression format, consisting of a backward-compatible superset.[11][12] 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).[12] VP3 video compression can be decoded using Theora implementations, but Theora video compression usually cannot be decoded using old VP3 implementations.

History

See also: VP3

Theora's predecessor On2 TrueMotion VP3 was originally a proprietary and patent-encumbered video codec developed by On2 Technologies. VP3.1 was introduced in May 2000[13] and followed three months later by the VP3.2 release,[14] which is the basis for Theora.

Move to free software

In August 2001, On2 Technologies announced that they would be releasing an open source version of their VP3.2 video compression algorithm.[15][16] In September 2001, On2 Technologies published the source code of the VP3.2 codec under the VP3.2 Public License 0.1,[17] a custom open-source license.[18][19] The license only granted the right to modify the source code if the resulting larger work continued to support playback of VP3.2 data.[17][20]

In March 2002, On2 responded to the public's reception by relicensing the VP3 codec under the GNU Lesser General Public License.[21] In June 2002, On2 donated VP3 to the Xiph.Org Foundation and offered it under the Ogg Vorbis BSD-style license.[22][23][24][25] 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.[11][26] 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.[27] 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.[28]

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][29]

Project Daala is working on the successor to Theora.

Theora I specification

Example of a Theora video used on Wikipedia, showing a Polikarpov I-15 biplane at an aerobatic display.

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][30] 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.[31] Any later changes in the specification are minor updates.

The Theora reference implementation libtheora spent several years in alpha and beta status.[30] The first alpha version was released on 25 September 2002[32] and the first beta version was released on 22 September 2007. The first stable release of libtheora was made in November 2008.[33][34] 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.[30][35] 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.[36]

Theora is well established as a video format in open source applications, and is the format used for Wikipedia's video content. However, the proposed adoption of Theora as part of the baseline video support in HTML5 resulted in controversy.[37]

Performance

Encoding performance

Evaluations of the VP3[38] and early Theora encoders[39][40][41] found that their subjective visual quality was inferior to that of contemporary video codecs. More recently however, Xiph developers have 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.[42] 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.[43][44]

The performance characteristics of the Theora 1.0 reference implementation are dominated mostly by implementation problems inherited from the original VP3 code base.[45] Work leading up to the 1.1 stable release was focused on improving on or eliminating these. A May 2009 review of this work shows a considerable improvement in quality, both subjectively and as measured by PSNR, just by improving the forward DCT and quantisation matrices.[46] A flaw in the version of FFmpeg used in the test initially led to incorrect reports of Theora PSNR surpassing that of H.264. Although not achieving this goal, the improvement in the measured PSNR and the perceived quality is considerable. In any case, the differences in quality, bitrate and file size between a YouTube H.264 video and a transcoded Ogg video file are negligible.[47] Further work on adaptive quantization, as well as overall detailed subjective tuning of the codec, is still to come.

Playback performance

There is an open source VHDL code base for a hardware Theora decoder in development.[48] It began as a 2006 Google Summer of Code project, and it has been developed on both the Nios II and LEON processors.[49] 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. But since decoding Theora is less CPU intensive than decoding H.264, the need for hardware-accelerated Theora decoding may be somewhat less.

Playback

Native browser playback

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

Browser plugins

Supporting media frameworks

Supporting applications

Encoding

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

Name Description Operating Systems Supported
Unix-like OS X Windows
Firefogg
 A Firefox browser extension implementation of ffmpeg2theora Yes Yes Yes
ffmpeg2theora
 A command-line program that transcodes video by decoding with FFmpeg and 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
OggConvert
 Transcodes supported media to Vorbis, Theora, or Dirac Yes ? Yes
FreeJ
 "Video DJing" software that can encode to and stream Theora Yes Yes ?
Kdenlive
 The video editor supplied with KDE Yes ? ?
Pitivi
 The video editor supplied with GNOME Yes ? ?
LiVES
 Video editing software for Linux. Can edit, encode and stream theora. Yes Yes ?
Thoggen
 A GTK+ and GStreamer based DVD backup utility Yes ? ?
HandBrake
 Can output to Theora only with the Matroska container 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 is still under development by the Xiph.Org Foundation. The library is released under the terms of a BSD-style license.

Also, several media frameworks have support for Theora.

Editing

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
 The KDE video editor. Yes ? ?
OpenShot
 Yes ? ?
Pitivi
 The GNOME video editor. Yes ? ?
Cinelerra
 CVS versions of the Cinelerra non-linear video editing system support Theora, as of August 2005. Yes Yes ?
oggz-tools by Xiph.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[69] Yes Yes Yes
AVS Video Editor
 ? ? Yes

Streaming

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
FreeCast
 Peer-to-peer streaming. Written in Java Yes ? Yes
LiVES
 Can stream ogg/theora/vorbis in realtime to a file or fifo. Yes Yes ?
Flumotion
 Streaming media server. Yes ? ?

Theora Streaming Studio is a complete client to connect to an Icecast server.

Makers

Elphel is the main maker of cameras that record in theora.

See also

References

  1. 1 2 3 Giles, Ralph (1 June 2004). "Theora I bitstream freeze". theora-dev (Mailing list). Retrieved 25 September 2009.
  2. 1 2 3 4 "Theora Specification" (PDF). Xiph.Org Foundation. 16 March 2011. Retrieved 31 January 2012.
  3. ↑ "PlayOgg! - FSF - Free Software Foundation". 2010-03-17. Retrieved 2013-10-01.
  4. ↑ "Theora 1.1.1 release". Xiph.Org Foundation. Retrieved 6 October 2009.
  5. ↑ "libtheora 1.2.0alpha1 release". Xiph.Org Foundation. Sep 2010. Retrieved 10 October 2010.
  6. ↑ Theora.
  7. ↑ Xiph.Org Foundation. "libtheora Documentation 1.1.0". Xiph.Org Foundation. Retrieved 25 September 2009.
  8. ↑ ohloh. "libtheora". ohloh. Retrieved 25 September 2009.
  9. ↑ "Theora FAQ". Xiph.Org Foundation. Retrieved 6 August 2009.
  10. ↑ "Matroska Codec Specs". Matroska. Retrieved 6 August 2009.
  11. 1 2 Xiph.org libtheora license (Subversion – Trunk), Retrieved on 16 August 2009
  12. 1 2 Xiph.org FAQ – Theora and VP3. Retrieved 2 September 2009
  13. ↑ On2 (17 May 2000), On2.com Launches Next Generation of Revolutionary Broadband Video Technology, archived from the original on 3 December 2007
  14. ↑ On2 (16 August 2000), On2 Introduces TrueMotion VP3.2, archived from the original on 3 December 2007, retrieved 23 August 2010
  15. ↑ On2 (7 August 2001), On2 Technologies to Open Source VP3.2 Video Compression Technology (archived website), archived from the original on 3 December 2007
  16. ↑ Mariano, Gwendolyn (7 August 2001). "On2's video codec to go open-source". CNET.
  17. 1 2 On2 Technologies (2001), VP3.2 Public License 0.1, Xiph.Org Foundation, retrieved 10 February 2008
  18. ↑ Bernat, Bill (7 September 2001). "On2 Offers Up VP3.2 Source Code". StreamingMedia.com.
  19. ↑ On2 (7 September 2001), On2 Technologies Makes Video Compression Technology Available to Open-Source Community, archived from the original on 7 December 2007
  20. ↑ Seibert, Stan (VP3.2 video codec open sourced). "VP3.2 video codec open sourced". vorbis (Mailing list). Check date values in: |date= (help)
  21. ↑ "On2 Alters Licensing Terms for VP3; Company Responds to Open Source Community Demands." (Press release). On2 Technologies. 28 March 2002.
  22. ↑ Xiph.Org Foundation (16 March 2011). "Theora Specification" (PDF). Xiph.Org Foundation. p. 1.
  23. ↑ On2 (24 June 2002), VP3 Combines with Vorbis to Create First Open-Source Multimedia Platform, archived from the original on 3 December 2007
  24. ↑ Linux.com (23 June 2002) Ogg Vorbis, VP3 combining forces to create Open Source multimedia package, Retrieved on 2009-08-16
  25. ↑ InternetNews.com (24 June 2002) On2 Throws More Open-Source at MPEG-4, Retrieved on 16 August 2009
  26. ↑ Xiph.org VP32 codec license (Subversion – Trunk), Retrieved on 16 August 2009
  27. ↑ The Free Library (1 August 2002) On2 Signs Pact With Xiph.org to Develop/Support VP3, Retrieved on 16 August 2009
  28. ↑ On2 (3 October 2002), On2 and Xiph Announce Alpha Code Release of Theora, VP3-Vorbis-Based Multimedia Solution, archived from the original on 4 December 2007
  29. ↑ Mike Melanson (mike at multimedia.cx) (8 December 2004), VP3 Bitstream Format and Decoding Process, Multimedia.cx, retrieved 27 September 2009
  30. 1 2 3 Xiph.Org Foundation (24 September 2009), Theora.org : news, Xiph.Org Foundation, retrieved 25 September 2009
  31. ↑ Xiph.Org Foundation (17 September 2004). "Theora I Specification, Xiph.org Foundation, September 17, 2004" (PDF). Archive.org. Archived from the original (PDF) on 28 September 2004. Retrieved 26 September 2009.
  32. ↑ https://git.xiph.org/?p=theora.git;a=blob_plain;f=CHANGES;hb=HEAD
  33. ↑ Giles, Ralph (3 November 2008). "Theora 1.0 final release!". theora-dev (Mailing list). Retrieved 4 November 2008.
  34. ↑ "The Xiph.Org Foundation announces the release of Theora 1.0" (Press release). Xiph.Org Foundation. 3 November 2008. Retrieved 6 August 2009.
  35. ↑ Giles, Ralph (24 September 2009). "libtheora 1.1 (Thusnelda) stable release". theora-dev (Mailing list). Retrieved 24 September 2009.
  36. ↑ Monty (18 May 2010). "Theora: Ptalarbvorm project update 20100518". Retrieved 1 July 2010.
  37. ↑ McLean, Prince (6 July 2009). "Ogg Theora, H.264 and the HTML 5 Browser Squabble". RoughlyDrafted Magazine. Retrieved 14 February 2010.
  38. ↑ "MPEG-4 Codec shoot-out 2002 – 1st installment". Doom9. 2002. Retrieved 19 December 2007.
  39. ↑ Codec shoot-out 2005 – Qualification, Doom9, 2005, retrieved 19 December 2007
  40. ↑ Loli-Queru, Eugenia (12 December 2007). "Theora vs. h.264". OSNews. Retrieved 1 April 2008.
  41. ↑ Halbach, Till (March 2009). "Dirac and Theora vs. H.264 and Motion JPEG2000". Retrieved 22 April 2008.
  42. ↑ DiBona, Chris (13 June 2009). "H.264-in- vs plugin APIs". whatwg (Mailing list). Retrieved 10 August 2009.
  43. ↑ Maxwell, Greg (13 June 2009). "YouTube / Ogg/Theora comparison". Xiph.Org Foundation. Retrieved 10 August 2009.
  44. ↑ Maik, Merten (15 June 2009). "Another online-video comparison". Xiph.Org Foundation. Retrieved 10 August 2009.
  45. ↑ Montgomery, Chris. "Theora "the push for 1.0" update". Retrieved 19 December 2007.
  46. ↑ Blizzard, Christopher. "Theora Update 7 May 2009". Retrieved 10 May 2009.
  47. ↑ Richmond, Gary. "Firefogg: Transcoding videos to open web standards with Mozilla Firefox". Retrieved 14 February 2010.
  48. ↑ "Xiph Subversion repository: trunk/theora-fpga". Xiph.Org Foundation. Retrieved 10 August 2009.
  49. ↑ "XiphWiki: Theora Hardware". Xiph.Org Foundation. Retrieved 10 August 2009.
  50. ↑ MozillaWiki (18 March 2009), Firefox3.5/Features, MozillaWiki, retrieved 11 October 2009
  51. ↑ Mozilla Corporation (30 June 2009), Mozilla Firefox 3.5 Release Notes, Mozilla Corporation, retrieved 11 October 2009
  52. ↑ Mozilla Corporation (9 February 2010), Firefox Mobile Features, Mozilla Corporation, retrieved 9 February 2010
  53. ↑ Google Chrome to support HTML 5 video, SoftSailor, 28 May 2009, retrieved 11 October 2009
  54. ↑ Stephen Shankland (28 May 2009), Google Chrome gets HTML video support, cnet news, retrieved 11 October 2009
  55. ↑ Issue 16657: Ensure FFmpeg binaries end up in snapshots on all platforms, google chromium issues list, 14 July 2009, retrieved 6 February 2010 horizontal tab character in |title= at position 15 (help)
  56. ↑ Robert Kaiser (16 September 2009), What's New in SeaMonkey 2.0 Beta 2, seamonkey-project.org, retrieved 11 October 2009
  57. ↑ Bugreport: Wish for audio/video element support in Konqueror, 13 May 2007, retrieved 2 December 2009
  58. ↑ Plans for Konqueror 4.4, 26 November 2009, retrieved 2 December 2009
  59. ↑ Philip Jägenstedt (31 December 2009). "(re-)Introducing [[File: – Official blog for Core developers at Opera". Opera. Archived from the original on 4 January 2010. Retrieved 2 January 2010.
  60. ↑ Arjan van Leeuwen (31 December 2009). "Happy New Year! – Official blog for Core developers at Opera". Opera. Archived from the original on 4 January 2010. Retrieved 2 January 2010.
  61. ↑ Experimental Opera-video build with native Ogg Theora support, Opera, 25 April 2007, archived from the original on 2 December 2007, retrieved 11 October 2009
  62. ↑ A call for video on the web – Opera = release on Labs, Opera, 7 November 2007, retrieved 11 October 2009
  63. ↑ alp (4 February 2010). "HTML5 Theora Video Codec for Silverlight". Alp Toker blog. Retrieved 14 February 2010. The Highgate media suite will bring installation-free support for HTML5 streaming video
  64. ↑ "ffdshow Summary". Retrieved 23 October 2009.
  65. ↑ Cutka, Milan (4 October 2002). "Theora support in ffdshow a ffvfw". theora-dev (Mailing list).
  66. ↑ "Theora in .ogg no only .avi – ffdshow tryouts Forum". 15 January 2008. Retrieved 23 October 2009.
  67. ↑ gstreamer.freedesktop.org. "GStreamer Base Plugins 0.10 (0.10.24.1)". Retrieved 23 October 2009.
  68. ↑ gstreamer.freedesktop.org. "GStreamer Base Plugins 0.10 Plugins Reference Manual – Theora plugin library". Retrieved 23 October 2009.
  69. ↑ Ogg Video Tools on SourceForge

External links

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