Theora
![]() | |
Filename extension |
.ogv, .ogg |
---|---|
Internet media type |
video/ogg |
Developed by | Xiph.org |
Initial release | 1 June 2004[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 |
Developer(s) | Xiph.org |
---|---|
Initial release | 3 November 2008 | (1.0)
Stable release | 1.1.1
/ 1 October 2009[4] |
Preview release | 1.2.0 Alpha 1
/ 24 September 2010[5] |
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[edit]
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[edit]
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[edit]
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.[citation needed] 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]
A successor to Theora, Daala, was later merged into AV1.[30]
Theora I specification[edit]
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][31] 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.[32] Any later changes in the specification are minor updates.
The Theora reference implementation libtheora spent several years in alpha and beta status.[31] The first alpha version was released on 25 September 2002[33] and the first beta version was released on 22 September 2007. The first stable release of libtheora was made in November 2008.[34][35] 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.[31][36] 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.[37]
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.[38]
Performance[edit]
Encoding performance[edit]
Evaluations of the VP3[39] and early Theora encoders[40][41][42] found that their subjective visual quality was inferior to that of contemporary video codecs. 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.[43] 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.[44][45]
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 leading up to the 1.1 stable release was focused on improving on or eliminating these. A May 2009 review of this work[by whom?] claimed a considerable improvement in quality, both subjectively and as measured by PSNR, just by improving the forward DCT and quantisation matrices.[47] 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.[48] Further work on adaptive quantization, as well as overall detailed subjective tuning of the codec, is still to come.[needs update]
Playback performance[edit]
There is an open-source VHDL code base for a hardware Theora decoder in development.[49][needs update] It began as a 2006 Google Summer of Code project, and it has been developed on both the Nios II and LEON processors.[50] 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.
Playback[edit]
![]() | This section contains embedded lists that may be poorly defined, unverified or indiscriminate. (June 2014) |
Native browser playback[edit]
As originally recommended by HTML 5, these browsers support Theora when embedded by the video
element:
- Mozilla Firefox 3.5 and later versions[51][52] including Firefox for mobile (Fennec).[53]
- Google Chrome as of version 3.0.182.2[54][55] including Chromium as of 14 July 2009.[56]
- Tizen browser
- SeaMonkey as of version 2.0.[57]
- Konqueror 4.4.2[58][59]
- Opera as of version 10.50.[60][61] It was also supported in Opera 9.5 experimental video builds.[62][63]
- 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+.
Browser plugins[edit]
- Annodex plugin via OggPlay[64]
- Cortado, a Java based applet
- Itheora, a PHP wrapper for Cortado
- Mv Embed[65] 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[66]
Supporting media frameworks[edit]
- 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.[67]
Supporting applications[edit]
- 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
Encoding[edit]
There are several third-party programs that support encoding through libtheora:
Name | Description | Operating Systems Supported | ||
---|---|---|---|---|
Unix-like | OS X | Windows | ||
|
A Firefox browser extension implementation of ffmpeg2theora | Yes | Yes | Yes |
A command-line program that transcodes video by decoding with FFmpeg and reencoding with libtheora to encode it | Yes | Yes | Yes | |
Can transcode to single-pass Theora 1.0 and optionally stream it | Yes | Yes | Yes | |
Transcodes supported media to Vorbis, Theora, or Dirac | Yes | ? | Yes | |
"Video DJing" software that can encode to and stream Theora | Yes | Yes | ? | |
The video editor supplied with KDE | Yes | ? | ? | |
The video editor supplied with GNOME | Yes | ? | ? | |
Video editing software for Linux. Can edit, encode and stream theora. | Yes | Yes | ? | |
A GTK+ and GStreamer based DVD backup utility | Yes | ? | ? | |
Can output to Theora only with the Matroska container | Yes | Yes | Yes | |
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.
- The open-source ffdshow audio/video decoder is capable of encoding Theora videos using its Video for Windows (VFW) multi-codec interface within popular AVI editing programs.[70][71][72] 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 aren't available to the user in ffdshow's interface.
- The GStreamer framework has support for parsing raw Theora streams, encoding and decoding raw Theora streams to/from YUV video[73][74]
Editing[edit]
Name | Description | Operating Systems Supported | ||
---|---|---|---|---|
Unix-like | OS X | Windows | ||
Video editing software for Linux. Can edit, encode and stream theora. | Yes | Yes | ? | |
The KDE video editor. | Yes | ? | ? | |
Yes | ? | ? | ||
The GNOME video editor. | Yes | ? | ? | |
CVS versions of the Cinelerra non-linear video editing system support Theora, as of August 2005. | Yes | Yes | ? | |
|
Command line programs to examine and edit Ogg files. | Yes | ? | Yes |
|
Tools to resize, cut, split, join, and others[75] | Yes | Yes | Yes |
? | ? | Yes |
Streaming[edit]
The following streaming media servers are capable of streaming Theora video:
Name | Description | Operating Systems Supported | ||
---|---|---|---|---|
Unix-like | OS X | Windows | ||
Yes | Yes | Yes | ||
Yes | ? | Yes | ||
Peer-to-peer streaming. Written in Java | Yes | ? | Yes | |
Can stream ogg/theora/vorbis in realtime to a file or fifo. | Yes | Yes | ? | |
Streaming media server. | Yes | ? | ? |
Makers[edit]
Elphel is the main maker of cameras that record in theora.
See also[edit]
References[edit]
- ^ a b c Giles, Ralph (1 June 2004). "Theora I bitstream freeze". theora-dev (Mailing list). Retrieved 25 September 2009.
- ^ a b c d "Theora Specification" (PDF). Xiph.Org Foundation. 16 March 2011. Retrieved 31 January 2012.
- ^ "PlayOgg! - FSF - Free Software Foundation". 17 March 2010. Retrieved 1 October 2013.
- ^ "Theora 1.1.1 release". Xiph.Org Foundation. Retrieved 6 October 2009.
- ^ "libtheora 1.2.0alpha1 release". Xiph.Org Foundation. September 2010. Retrieved 10 October 2010.
- ^ Theora.
- ^ Xiph.Org Foundation. "libtheora Documentation 1.1.0". Xiph.Org Foundation. Retrieved 25 September 2009.
- ^ ohloh. "libtheora". ohloh. Retrieved 25 September 2009.
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- ^ a b Xiph.org FAQ – Theora and VP3. Retrieved 2 September 2009
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- ^ Mariano, Gwendolyn (7 August 2001). "On2's video codec to go open-source". CNET.
- ^ a b On2 Technologies (2001), VP3.2 Public License 0.1, Xiph.Org Foundation, retrieved 10 February 2008
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- ^ On2 (7 September 2001), On2 Technologies Makes Video Compression Technology Available to Open-Source Community, archived from the original on 7 December 2007
- ^ Seibert, Stan (September 2001). "VP3.2 video codec open sourced". vorbis (Mailing list).
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- ^ Xiph.Org Foundation (16 March 2011). "Theora Specification" (PDF). Xiph.Org Foundation. p. 1.
- ^ On2 (24 June 2002), VP3 Combines with Vorbis to Create First Open-Source Multimedia Platform, archived from the original on 3 December 2007
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- ^ Giles, Ralph (24 September 2009). "libtheora 1.1 (Thusnelda) stable release". theora-dev (Mailing list). Retrieved 24 September 2009.
- ^ Monty (18 May 2010). "Theora: Ptalarbvorm project update 20100518". Retrieved 1 July 2010.
- ^ McLean, Prince (7 July 2009). "Ogg Theora, H.264 and the HTML 5 Browser Squabble". AppleInsider. Retrieved 1 November 2020.
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- ^ OggPlay
- ^ Mv Embed Archived 4 August 2008 at the Wayback Machine
- ^ https://www.microsoft.com/en-us/p/web-media-extensions/9n5tdp8vcmhs?activetab=pivot:overviewtab
- ^ 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
- ^ Firefogg
- ^ ffmpeg2theora
- ^ "ffdshow Summary". Retrieved 23 October 2009.
- ^ Cutka, Milan (4 October 2002). "Theora support in ffdshow a ffvfw". theora-dev (Mailing list).
- ^ "Theora in .ogg no only .avi – ffdshow tryouts Forum". 15 January 2008. Retrieved 23 October 2009.
- ^ gstreamer.freedesktop.org. "GStreamer Base Plugins 0.10 (0.10.24.1)". Retrieved 23 October 2009.
- ^ gstreamer.freedesktop.org. "GStreamer Base Plugins 0.10 Plugins Reference Manual – Theora plugin library". Retrieved 23 October 2009.
- ^ Ogg Video Tools on SourceForge