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

[D Richard Felker III]

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.

rich