Re[2]: [XviD-devel] xvid + bframes and mplayer/ffmpeg decoding

[Christoph Lampert]

On Fri, 16 Aug 2002, Michael Niedermayer wrote:

> Hi
> 
> On Friday 16 August 2002 14:50, Christoph Lampert wrote:
> > On Fri, 16 Aug 2002, Radoslaw Czyz wrote:
> > > > Ouch! Is this in the standard? Where? Is this for B-frames, too?
> note 2 in 7.4.4.5

Double ouch! I guess we don't do anything of 7.4.4.5. "Mismatch
control"... 

This states that (for H263?) the sum of all unquantized coefficients
must be calculated and if the result is _even_ then the last coefficient
dct_codes[63] has to be changed by 1. 
So we should adapt deQuant to include this, or is it already? 

There are two tips, too: 
1) Since only even/odd is important, we could also XOR the coefficients,
or even only XOR the last bit. 
2) To change the coefficient 63, it's enough to flip the last bit.  

Thanks for pointing that out!

And, of course the "DCT!=0 -> iDCT==0" thing... Maybe we should simply 
disable quant=1, I guess than the problem would be more or
less solved... ;-)

gruel


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