[MPlayer-dev-eng] -vc ffmpeg2 speedup trick

[Attila Kinali]

On Thu, Sep 02, 2004 at 10:13:39AM -0400, D Richard Felker III wrote:
> On Thu, Sep 02, 2004 at 04:56:49AM +0200, Michael Niedermayer wrote:
> > Hi
> > 
> > try '-lavdopts idct=4'
> > 
> > the reason why this is faster then the default idct is that the default one 
> > checks for zero coefficients, which are _very_ common to avoid useless 
> > calculations, but the dequantization used in mpeg2 messes with the least 
> > significant bit of coefficient 63, which causes it to be non zero very 
> > often ...
> 
> ok, how about this: could we have an option to do coeff[63]&=~1; for
> mpeg2, or something similar? mpeg2 always uses tiny gop sizes so the
> accumulated error probably wouldn't be visible, and it could be a huge
> performance boost.

Althoug i'm not an codec expert, this sounds like something we should
do. Especial on borderline hardware this would give some space to
breath. And as high res MPEG2 streams (aka HDTV) seem to spread more and
more, we might get such borderline hardware again.


			Attila Kinali