[theora-dev] VP3 Format Doc, v0.4

Michael Niedermayer michaelni at gmx.at
Thu Mar 4 11:33:35 PST 2004


On Wednesday 03 March 2004 08:14, Mike Melanson wrote:
> Hi,
> 	Check it out-- another update in the space of a week:
>   http://home.pcisys.net/~melanson/codecs/vp3-format.txt
> v0.4: March 2, 2004
> - renamed and expanded section "Initializing The Quantization Matrices"
> - outlined section "Reconstructing The Frame"
> - moved Theora Differences Appendix to its own section entitled "Theora
> Specification"
> - added Appendix: Quantization Matrices And Scale Factors
> - added Appendix: DCT Coefficient VLC Tables
> I have now made the Theora spec more than a footnote in the document
> (though I still have not expounded much upon that section).
> 	Happy reading...
a few comments ...
* the intra quantization matrixes are from jpeg (maybe u want to menton that)

* u dont mention which rounding variant is used in divisions, its quite 
obvious from the examples though

* i think u didnt mention in what order macroblocks are stored in the 
bitstream, but maybe i missed it

* maybe it would help readability of the dc prediction description if there 
where a table for the 16 fragment availability cases and which are 
used/discarded, something like:
0 0 0 0 uses 0
0 0 0 1 uses UR
1 0 1 0 uses (L+U)/2

* the VP3/theora code contains deblock/dering filters IIRC, are these optional 
in a sense that they are applied to every image but the decoder uses the 
unfiltered image for motion compensaton, or are these loop filters which are 
used in the decode-mc loop?

* i think theres no mentioning of the motion vector accuracy, are they 1/2 

* theres also no explanation of how the halfpel motion compensation is done 
(rounding?), and what is done for the chroma fragments, the motion vector is 
1/4 pel accurate for them if its 1/2 pel for luma

btw, very nice doc :)


level[i]= get_vlc(); i+=get_vlc();		(violates patent EP0266049)
median(mv[y-1][x], mv[y][x-1], mv[y+1][x+1]);	(violates patent #5,905,535)
buf[i]= qp - buf[i-1];				(violates patent #?)
for more examples, see http://mplayerhq.hu/~michael/patent.html
stop it, see http://petition.eurolinux.org & http://petition.ffii.org/eubsa/en

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