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Theora
From Wikipedia, the free encyclopedia
| Theora | |
|---|---|
| File extension: | .ogv |
| MIME type: | video/ogg |
| Developed by: | Xiph.Org Foundation |
| Type of format: | Video codec |
| Contained by: | Ogg |
| Standard(s): | Specification |
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The introduction to this article provides insufficient context for those unfamiliar with the subject. Please help improve the article with a good introductory style. |
Theora is a video compression technology being developed by the Xiph.Org Foundation as part of their Ogg project. Based upon On2 Technologies' VP3 codec, and christened by On2 as the successor in VP3's lineage, Theora is targeted at competing with MPEG-4 video (e.g., the x264, Xvid and DivX codecs), RealVideo, Windows Media Video, and similar lower-bitrate video compression schemes.
While VP3 is patented technology, On2 has irrevocably given royalty-free license of the VP3 patents to everyone, letting anyone use Theora and other VP3-derived codecs for any purpose.
In the Ogg multimedia framework, Theora provides a video layer, while Vorbis usually acts as the audio layer. Speex, FLAC, and OggPCM may also act as audio layers.
Theora is named for Theora Jones, Edison Carter's Controller on the Max Headroom television program.
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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. Theora uses block based motion compensation and an 8x8 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]
VP3 was originally a proprietary video codec developed by On2 Technologies. VP3 and Theora are approximately comparable in quality and bit rate to MPEG-1 video codecs, but substantially lacking compared to the contemporary video codecs. [2][3]
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. In 2002, On2 entered into an agreement with the Xiph.Org Foundation to make VP3 the basis of a new, free video codec, Theora.
As of December 2007, Theora is in final beta stage before the official release of version 1.0. The bitstream format was frozen with alpha 3 (July 2004), so video encoded in current and older versions of Theora is compatible with any player.
- 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)
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 two 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 2006, 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.
- 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.
CVS versions of the Cinelerra non-linear video editing system support Theora, as of August 2005.
The following streaming media servers are capable of streaming Theora video:
- 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)
- ^ http://theora.org/doc/Theora_I_spec.pdf
- ^ Doom9 (2005), Codec shoot-out 2005 - Qualification, <http://www.doom9.org/codecs-quali-105-3.htm>. Retrieved on 2007-12-10
- ^ , <http://web.mit.edu/xiphmont/Public/theora/demo.html>. Retrieved on 2007-12-10
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| Ogg Project | Vorbis · Theora · FLAC · Speex · Tremor · OggUVS · OggPCM |
| Other projects | XSPF · Annodex · Xiph QuickTime Components · cdparanoia · Icecast · IceShare |
| Related articles | Chris Montgomery · CMML · Ogg Media · Ogg page · Ogg Squish |