Theora
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| Theora | |
|---|---|
| File name extension | .ogv (was .ogg in the past) |
| Internet media type | video/ogg |
| Developed by | Xiph.Org Foundation |
| Type of format | Video codec |
| Contained by | Ogg |
| Extended from | VP3 |
Theora is an open and royalty-free lossy video compression technology being developed by the Xiph.Org Foundation as part of their Ogg project. Based upon On2 Technologies' VP3 codec, Theora is targeted at competing with MPEG-4, WMV, and similar low-bitrate video compression schemes.
Theora is named for Theora Jones, Edison Carter's Controller on the Max Headroom television program.
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[edit] Technical details
Theora is a lossy video compression method derived from On2's VP3 Codec. The compressed video can be stored in any suitable container format. At the time of writing (June 2006), Theora video is generally included in Ogg container format. It is frequently paired with Vorbis audio.
The combination of the Ogg container format, Theora video and Vorbis audio allows for a completely open, royalty-free multimedia format. Other multimedia formats, such as MPEG-4 video and MP3 audio, are patented and subject to license fees for commercial use.
Like many other image and video formats, Theora uses Chroma subsampling, block based motion compensation and an 8×8 DCT block. This is comparable to MPEG-1/2/4. It supports intra coded frames and forward predictive frames but not bi-predictive frames that can be found in many other video codecs. [1]
[edit] VP3
VP3 was originally a proprietary and patented video codec developed by On2 Technologies. In September, 2001 VP3 was donated to the public as free and open source software, and On2 disclaimed all rights to it, including their patents on the technology, letting anyone use Theora and other VP3-derived codecs for any purpose.[2] In 2002, On2 entered into an agreement with the Xiph.Org Foundation to make VP3 the basis of a new, free video codec, Theora. On2 christened Theora as the successor in VP3's lineage.
[edit] Current status
As of May 2008, Theora is in final beta stage (1.0 beta 3) before the official release of version 1.0. The bitstream format was frozen with alpha 3 (July 2004), so videos encoded with any version of Theora since that time will continue to be compatible with any future player.
[edit] Performance
Previous evaluations have found VP3[3] and Theora[4] [5] substantially lacking compared to contemporary video codecs (having been called comparable in quality and bit rate to H.261,[6] although some dispute this point).
[edit] Efforts to improve performance
Sources close to Xiph.org have stated that the performance characteristics of the current Theora reference implementation are mostly dominated by implementation issues inherited from the original VP3 code base. An internal document exists, which lists the known implementation problems and gives an example of how improving one aspect of the encoder can lead to visibly improved quality.[7] Current work on Theora is focused on an experimental version, which targets correcting aspects of the encoder which were identified in that paper as being suboptimal. This experimental version is supposed to replace the current encoder in a future Theora release.
[edit] Playing Theora
- See also Wikipedia:Media help (Ogg)
- Cortado, a Java based applet
- Itheora, a PHP wrapper for Cortado
- FFmpeg (own implementation)
- MPlayer and front-ends
- RealPlayer
- Helix Player
- VLC (native support)
- xine and all libxine-based players like Kaffeine
- Totem
- QuickTime 7
- Visonair.tv Player
- Miro Media Player (formerly known as Democracy Player)
[edit] Encoding Theora videos
The libtheora library contains the reference implementations of both the Theora encoder and decoder. libtheora is still under development by the Xiph.Org Foundation, which has made eight alpha releases and 3 major beta release thus far which include a complete rewrite of the decoder. The library is released under the terms of a BSD-style license.
As of 2008, the Xiph.Org Foundation has not developed any stand-alone programs to encode video in Theora, but there are several third-party programs that support encoding through libtheora:
- ffmpeg2theora uses FFmpeg to decode video and libtheora to encode it. This is currently the most functional Theora encoder, and can be used for both creating stand-alone video files and to produce streaming video.
- VLC is able to encode Theora video, from any of the video sources it supports, and also stream it, although version 0.8 has had some problems with encoding Theora on the Mac OS X release.
- The open-source OggConvert [1] utility can convert virtually all common media formats to Theora.
- The open-source 'Video DJ' program FreeJ can encode and stream Theora. Video comes from one or more different video or image files/sources while audio is encoded from the soundcard.
- The GNOME video editor Diva encodes to Theora.
- The freeware Super program can transcode between Theora and almost any other format.
- The open-source Video Editing program LiVES can also encode to Theora at different quality settings.
- There is also currently a beta-version of Thoggen [2] for Linux, a GTK+ and GStreamer based DVD-backup utility, which encodes to Vorbis and Theora.
- KungFu DVD Ripper [3]
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 such as VirtualDub. 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 Theora.
[edit] Editing Theora videos
CVS versions of the Cinelerra non-linear video editing system support Theora, as of August 2005.
[edit] Streaming Theora
The following streaming media servers are capable of streaming Theora video:
[edit] See also
[edit] References
- ^ http://theora.org/doc/Theora_I_spec.pdf
- ^ VP3.2 Public License 0.1, 2001, <http://trac.xiph.org/browser/branches/vp32/vp32/VP32_license.txt>. Retrieved on 10 February 2008
- ^ Doom9 (2002), MPEG-4 Codec shoot-out 2002 - 1st installment, <http://www.doom9.org/codec-comparisons.htm>. Retrieved on 19 December 2007
- ^ Doom9 (2005), Codec shoot-out 2005 - Qualification, <http://www.doom9.org/codecs-quali-105-3.htm>. Retrieved on 19 December 2007
- ^ Loli-Queru, Eugenia (December 12, 2007), Theora vs. h.264, OSNews, <http://ww.osnews.com/story/19019/Theora-vs-h.264/>. Retrieved on 1 April 2008
- ^ Wenger, Stephan (December 12, 2007), Web Architecture and Codec Considerations for Audio-Visual Services, pp. 3, <http://www.w3.org/2007/08/video/positions/Nokia.pdf>. Retrieved on 19 December 2007
- ^ Montgomery, Chris, Theora "the push for 1.0" update, <http://web.mit.edu/xiphmont/Public/theora/demo.html>. Retrieved on 19 December 2007
[edit] External links
- Theora.org
- Theora I Specification
- Building a Theora camera using an FPGA and embedded Linux
- ffmpeg2theora
- v2vwiki's list of Theora players
- List of Theora videos — downloadable videos encoded with Theora
- Why Theora Matters for Internet TV
- Theora on Danish Public TV? — DR (Danmarks Radio - Denmark's primary public TV station) is currently evaluating Theora as an alternative to Windows Media (Danish)
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