https://wiki.xiph.org/api.php?action=feedcontributions&user=Sparrish&feedformat=atomXiphWiki - User contributions [en]2024-03-28T11:08:40ZUser contributionsMediaWiki 1.40.1https://wiki.xiph.org/index.php?title=Theora&diff=2240Theora2005-11-29T01:39:17Z<p>Sparrish: /* External links */</p>
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<div>'''Theora''' is our 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.<br />
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== Features ==<br />
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Features available in the Theora Format (and a comparison to VP3 and MPEG-4 ASP):<br />
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* block-based motion compensation<br />
* 8x8 Type-II Discrete Cosine Transform<br />
* free-form variable bit rates (VBR)<br />
* adaptive in-loop deblocking applied to the edges of the coded blocks (not existing in MPEG-4 ASP)<br />
* block sizes down to 8x8 (MPEG-4 ASP supports normally only 16x16)<br />
* 384 8x8 custom quantization matrices: intra/inter, luma/chroma and even each quant (more than VP3 and MPEG-4 ASP/AVC)<br />
* adaptive entropy encoding (MPEG-4 ASP does'nt support adaptivity)<br />
* 4:2:0, 4:2:2, and 4:4:4 chroma subsampling formats (VP3 and MPEG-4 ASP only support 4:2:0)<br />
* 8 bits per pixel per color channel<br />
* multiple reference frames (not possible in MPEG-4 ASP)<br />
* pixel aspect ratio (eg for anamorphic signalling/playback)<br />
* non-linear scaling of quants values (as done in MPEG-4 AVC)<br />
* adaptive quantisation down to the block level (as possible in MPEG-4 ASP/AVC)<br />
* intra frames (I-Frames in MPEG), inter frames (P-Frames), but no B-Frames (as supported in MPEG-4 ASP/AVC)<br />
* HalfPixel Motion Search Precision (MPEG-4 ASP/AVC supports HalfPixel or QuarterPixel)<br />
* technologies used already in Vorbis (decoder setup configuration, bitstream headers...) not available in VP3<br />
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Note that not all of these features are already implemented in the reference encoder/decoder.<br />
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== Status ==<br />
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Alpha 5 is the latest release. The bitstream format is frozen. Every file created with the alpha 3 encoder (and, of course, later encoders) will be playable with future decoders. Beta 1 will be the next release.<br />
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* It would be nice if somewhere it could be explained if Theora is a format appropriate for editing video - such formats would not do frame to frame compression and the file size and processor load would be smaller. On the other hand a distribution format would want to pack in a lot of compression which would mean using frame to for compression.<br />
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== Development ==<br />
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* [[Theora:Beta1ToDo|Todo for Beta1]]<br />
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== More information ==<br />
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* [[TheoraHardware]]: List of hardware-players supporting Ogg Theora<br />
* [[TheoraSoftwarePlayers]]: List of media players that can play Ogg Theora<br />
* [[TheoraDecoders]]: List of decoders<br />
* [[TheoraEncoders]]: List of encoders<br />
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== External links ==<br />
<br />
* [http://www.theora.org/ Theora homepage]<br />
* [http://www.annodex.net/software/theora/ Theora documentation daily builds]<br />
* [[Wikipedia: Theora]]<br />
* [http://www.vp3.com VP3 homepage]: The homepage of the codec Theora is based on<br />
* [http://www.on2.com On2 Technologies]: The creators of VP3<br />
* [http://forum.doom9.org/showthread.php?s=&threadid=77314 Ogg Theora Information on Doom9 Forum]<br />
* [http://www.parrishtech.com/content/view/16/1/ HOWTO: Rip DVD to Theora using Linux]</div>Sparrish