From Wikipedia, the free encyclopedia

Jump to: navigation, search
Filename extension .ogv
Internet media type video/ogg
Developed by
Type of format Video codec
Contained by Ogg
Extended from VP3
Standard(s) Specification
Developed by
Latest release 1.0 / 2008-11-3; 154 days ago[1]
Operating system Unix-like, Microsoft Windows
License 3-clause BSD

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 competes 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.


[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. Theora video is generally included in Ogg container format and is frequently paired with Vorbis format audio streams.

The combination of the Ogg container format, Theora-encoded video, and Vorbis-encoded 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 by 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.[2]

[edit] History

VP3 was originally a proprietary and patented video codec developed by On2 Technologies. In September 2001 On2 donated VP3 to the public as free and open source software and disclaimed all rights to it (including their patents on the technology) letting anyone use Theora and other VP3-derived codecs for any purpose.[3] 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 declared Theora to be the successor in VP3's lineage.

[edit] Current status

After several years of beta status, Theora released its first stable (1.0) version, in November 2008. However, since the bitstream format was frozen in 2004 (version 1.0alpha3), videos encoded with any version of Theora since that time will continue to be compatible with any future player[4]. Current work is now focused on stabilizing the experimental "Thusnelda" branch for integration into the future 1.1 release[5].

[edit] Performance

Previous evaluations have found VP3[6] and Theora[7][8] inferior compared to contemporary video codecs. In particular, Theora has inferior picture quality and network frame rate control.

[edit] Efforts to improve performance

Sources close to 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 that lists the known implementation problems and gives an example of how improving one aspect of the encoder can lead to visibly improved quality.[9] Current work on Theora is focused on completing the 1.0 release of the reference codec, libtheora; following the 1.0 release, the thusnelda branch will be integrated into the future version 1.1 release.

[edit] Playback

[edit] In-browser playback

[edit] Supporting media frameworks

[edit] Supporting applications

... and many more via supported frameworks listed above

[edit] Encoding

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 (except for the example encoder), but there are several third-party programs that support encoding through libtheora:

Description Operating Systems Supported
  Linux Mac OS X Windows
firefogg[10] is a firefox browser extension version of ffmpeg2theora. Firefogg enables in browser transcoding of many video formats. Encoding settings are provided by the web service, transcoding happens on the clients computer then an "upload in chunks" api enables reusable transfers of the video to the web server. Yes Yes Yes
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. Yes Yes Yes
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. Yes Yes Yes
The open-source OggConvert[11] utility can convert virtually all common media formats to Theora. Yes   Almost
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. Yes Yes  
The GNOME video editor Diva encodes to Theora. Yes    
The freeware Super program can transcode between Theora and almost any other format.     Yes
The open-source Video Editing program LiVES can also encode to Theora at different quality settings. Yes Yes  
There is also currently a beta-version of Thoggen[12] for Linux, a GTK+ and GStreamer based DVD-backup utility, which encodes to Vorbis and Theora. Yes    
KungFu DVD Ripper[13] Yes    

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

Description Operating Systems Supported
  Linux Mac OS X Windows
CVS versions of the Cinelerra non-linear video editing system support Theora, as of August 2005. Yes Yes  

[edit] Streaming

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

Description Operating Systems Supported
  Linux Mac OS X Windows
VLC Yes Yes Yes
Icecast Yes  ? Yes
FreeCast, a Java peer-to-peer streaming solution Yes  ? Yes
Flumotion streaming media server Yes    

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

[edit] See also

[edit] References

[edit] External links

Personal tools