Theora is anopen video codec being developed by the Xiph.org Foundation as part of their Ogg project (It is a project that aims tointegrate On2'sVP3 video codec, OggVorbis audio codec and Ogg multimedia container formats into a multimedia solution that can compete withMPEG-4 format).
Theora is derived directly from On2's VP3 codec; currently the two are nearly identical, varying only in framing headers, but Theora will diverge and improve from the main VP3 development lineage as time progresses.

It's open and free. Have a look at theTheora benefits section for further information.

Theora is targeted at competing with MPEG-4 (e.g., XviD and DivX), RealVideo, Windows Media Video, and similar lower-bitrate video compression schemes.

Vorbis is an audio codec, Theora is a video codec. Ogg is the transport layer that both are stored in, so a video file will be Theora-encoded data inside an Ogg file, while audio is normally Vorbis-encoded data inside an ogg file.
TheXiph.org Foundation is a Delaware non-profit company devoted to producing, maintaining and supporting an open multimedia platform.

Theora (and all associated technologies released by the Xiph.orgFoundation) is released to the public via a BSD-style license. It iscompletely free for commercial or noncommercial use. That means thatcommercial developers may independently write Theora software which iscompatible with the specification for no charge and without restrictions ofany kind.

Like other Xiph.org Foundation codec projects such as Vorbis or Tarkin,Theora is named after a fictional character. Theora Jones was the name ofEdison Carter's 'controller' on the television series Max Headroom. She wasplayed by Amanda Pays.

Yes and No. Theora is a superset of VP3, so VP3 streams (with minorsyntactic modifications) can be made into Theora streams withoutrecompression (but not vice versa).

The major change from VP3 to Theora is architectural. VP3, like mostcodecs of today, makes certain assumptions about the nature of the materialit compresses. These assumptions take the form of fixed sets of numericvalues, such as quantization matrices, which control how differentfrequency components of the signal are handled, and token frequency tables,which control the efficiency of post-transform lossless coding. In Theora,we have leveraged the intrinsic flexibility of the Ogg multimedia frameworkto allow the encoder to modify these values appropriately for the material.This simple, powerful approach has already been proven effective in Vorbis,and will allow for a longer cycle of encoder optimization without requiringclient-side updates.

Because Theora is a 'superset' of VP3, tools can easily be created thatwill allow VP3 files to be losslessly transcoded into Ogg Theora formatwith no loss in quality.

Why would you want to do something like that? Are you nuts?

The Xiph.org Foundation has negotiated an irrevocable free license from On2 to the VP3 codec.It is legal touse VP3 in any way you see fit (unless, of course, you're doing somethingillegal with it in your particular jurisdiction). You are free to downloadVP3 and Theora, use them free of charge, implement them in a for-sale product, implement them in a free product, make changes to the source and distribute those changes, or print the source code out and wallpaper your spare room with it.
For more information, check the VP3 Legal Terms on the SVN page.

Because Theora is an Open Source project, the source code will continue tobe available and development will continue. Users will still be protectedfrom the On2 patents.

The bitstream format was frozen after the release of libtheora 1.0 alpha 3 in 2004. Files produced by the alpha 3 reference encoder will be supported by all future decoders.

Thusnelda was the codename of the encoder rewrite subsequent to the 1.0 release. It offered significant improvements in output quality.

Tarkin was a proof-of-concept wavelet-based codec. It was never ready for general use. Xiph.org is focusing its efforts on Theora and Dirac for the foreseeable future.

Head on over to theGit page to grab the codebase, and hack away! Post your contributions online, and tell us about it on theTheora-dev mailing list.

As the Ogg Vorbis format has gained acceptance, components have becomeavailable to play Ogg files on practically all of the major media players.We expect a similar if not superior level of support for Ogg Theora. The open source Firefox and Chrome web browsers have native Theora playback as part of their media element (<video>) element support.

Wow, thanks! You can find more information on donating to the Xiph.orgFoundation by followingthis link! Thanks in advance!

Major players likemplayer,xine,helix player andVideoLAN supports Theora. Directshowfiltersare also available for use on Windows platform.

There's amore complete list of playersavailable at the xiph.org wiki.

Have a look atogg-theora-microhowto andtranscodequicktime mov files to Theora files under Linux.You can use libogg, to wrap theora video with vorbis audio in Oggfile.

A user-friendly way to convert .dv and .avi format video into Ogg Theora format is with ffmpeg2theora. It can be found at: http://www.v2v.cc/~j/ffmpeg2theora/

A way to both stream and encode theora format video is with videolan (VLC).
Example for streaming the video4linux device in ogg theora/vorbis:

vlc v4l:/dev/video:input=3:norm=pal:size=384x288 --sout \
'#transcode{vcodec=theora,vb=300,acodec=vorb,ab=96}:std{access=http,mux=ogg,url=server.example.org:8000}'

Or, replace "v4l:/dev/video:input=3:norm=pal:size=384x288" with a filename if you want to transcode.

For more on the vlc syntax, see:
http://videolan.org/doc/videolan-howto/en/ch09.html

Yes, you can use your Theora files on windows usingDirectshow filters.FFdshow also has support for Theora. You can also tryvlc, realplayerTheora plugins ormplayer for windows.

The VP3 codec that serves as the base ofTheora was written by a company calledOn2 Technologies. Xiph.org is responsible for all aspects of on going development.

No one person at the moment. Send changes to the list if it needs them. Itwas originally written by Emmett Plant and Dan Miller. This FAQ wouldn't behere at all without the work of Slammin' Stan Seibert, to whom we areeternally grateful.