Theora

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Theora is a video codec 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., H.264, Xvid and DivX), 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 and FLAC can also act as audio layers).

Theora is named for Theora Jones, Edison Carter's Controller on the Max Headroom television program.

1 Technical details
2 VP3
3 Encoding Theora videos
4 Editing Theora videos
5 Playing Theora videos
- 5.1 List of Theora video players
6 Streaming Theora
7 See also
8 External links

[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. Previous multimedia formats (e.g. MPEG-4 video and MP3 audio) were patented, meaning that Free Software players implementing them were legally vulnerable, because paying license fees for software freely available for everyone to use anywhere for anything is often hard, if not impossible to do, regardless of whether licensing fees are rarely collected or not. Like many other image and video formats, Theora uses Chroma subsampling.

[edit] VP3

VP3 was originally a proprietary video codec developed by On2 Technologies. It is approximately comparable in quality and bit rate to MPEG-1 video codecs.

In September, 2001 it was donated to the public as open source, 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, Ogg Theora. It can be operated alongside Ogg Vorbis to provide a set of open source multimedia codecs that are intended to be free of patent licensing restrictions and royalty fees. Theora is currently still in alpha stage. However, the bitstream format was frozen with alpha 3, therefore video encoded with the current codec will be playable by future versions of the Theora decoder.

[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 seven alpha releases thus far. The library is released under the terms of a BSD-style license.

As of 2006, Xiph.Org 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 ogg/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 Ogg Theora.
The open-source Video Editing program LiVES can also encode to ogg 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 Ogg (Vorbis audio, Theora video).
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.