Theora

2010-07-07T21:46:45Z

ArcangelaGallo: /* Features */

'''Theora''' is a video codec, based on the [[VP3]] codec donated by [[On2 Technologies]]. We've refined and extended it, giving it the same future scope for encoder improvement [[Vorbis]] has. See http://theora.org/ for more information.

== Features ==

Features available in the Theora format (and a comparison to VP3 and MPEG-4 ASP):

* [http://www.customessaywritinghelp.com/ custom essay writing]
* 8x8 Type-II Discrete Cosine Transform
* block-based motion compensation
* free-form variable bit rates (VBR)
* adaptive in-loop deblocking applied to the edges of the coded blocks (not existing in MPEG-4 ASP)
* block sizes down to 8x8 (MPEG-4 ASP supports 8x8 only with 4MV)
* 384 8x8 custom quantization matrices: intra/inter, luma/chroma and even each quant (more than VP3 and MPEG-4 ASP/AVC)
* flexible entropy encoding (Theora supports 80 VLC tables selectable per-frame, MPEG-4 ASP has just one)
* 4:2:0, 4:2:2, and 4:4:4 chroma subsampling formats (VP3 and MPEG-4 ASP only support 4:2:0)
* 8 bits per pixel per color channel
* multiple reference frames (not possible in MPEG-4 ASP)
* pixel aspect ratio (eg for anamorphic signalling/playback)
* non-multiple of 16 picture sizes (as possible in ASP, but not in VP3)
* non-linear scaling of quants values (as done in MPEG-4 AVC)
* adaptive quantization down to the block level (as possible in MPEG-4 ASP/AVC, but not in VP3)
* intra frames (I-Frames in MPEG), inter frames (P-Frames), but no B-Frames (as supported in MPEG-4 ASP/AVC)
* HalfPixel Motion Search Precision (MPEG-4 ASP/AVC supports HalfPixel or QuarterPixel)
* technologies used already in Vorbis (decoder setup configuration, bitstream headers...) not available in VP3

== Status ==
* '''1.1.1''' is the latest stable release (2009-10-01).
* The bitstream format was frozen in 1.0 Alpha 3 on 2004-08-04: every file created with this encoder (and, of course, later encoders) will be playable by any compliant Theora decoder.
* The decoder in 1.0 Alpha 8 implemented all features of the [http://theora.org/doc/Theora.pdf Theora Format Specification]: every file created by any compliant Theora encoder will be playable by the decoder in 1.0 Alpha 8 (and, of course, later decoders).

== Development ==

* [[OggTheora|Mapping in Ogg]]
* [[TheoraTodo|ToDo list for development]]
* [[Cortado/release|Release checklist for the Cortado java applet]]

== More information ==
{{Template:Theora}}

It's possible to convert VP3 video to Theora. See [[vp3toTheora]].

== External links ==

* [http://www.theora.org/ Theora homepage]
* [http://www.annodex.net/software/theora/ Theora documentation daily builds]
* [[Wikipedia: Theora]]
* [http://www.vp3.com VP3 homepage]: The homepage of the codec Theora is based on
* [http://www.on2.com On2 Technologies]: The authors of VP3
* [http://forum.doom9.org/showthread.php?s=&threadid=77314 Ogg Theora Information on Doom9 Forum]
* [http://www.parrishtech.com/content/view/16/1/ HOWTO: Rip DVD to Theora using Linux]
* [http://www.doom9.org/index.html?/codecs-quali-105-1.htm Codec shoot-out 2005] Comparison of many video codecs, including Theora

[[Category:Theora]]

XiphWiki - User contributions [en]

Theora