[FFmpeg-devel] [RFC] AAC Encoder

Michael Niedermayer michaelni
Mon Aug 18 13:07:10 CEST 2008

On Mon, Aug 18, 2008 at 10:01:56AM +0300, Kostya wrote:
> On Sun, Aug 17, 2008 at 04:41:39PM +0200, Michael Niedermayer wrote:
> > Besides a psychoacoustic model IMHO produces perceptual weights, either per
> > bands or coefficients.
> > Everything else should be done per RD theory.
> > Now in principle other decissions could also be done on a psychoacoustic
> > aware way but as we have seen from the quantization this is clearly not the
> > case in the current model.
> > What the current model does is it calculates these weights (in the form of
> > scale factors) and the rest has absolutely nothing to do with psychoacoustics
> > its just a trivial reference quantizer, trivial M/S selection based on better
> > decorrelation, trivial IIR filter based short window selection [and this one
> > is even suboptimal in its own way as it limits itself to 9 out of 128
> > groupings].
> > the scalefactors from the psy model should be useable as RD factors for
> > weighting between rate and distortion. Iam pretty sure a relation like
> > lambda = A*sf^B  with A and B constants should be more than good enough
> > for our purposes, it is for mpeg4 ASP. I guess loren or dark shikari can
> > comment on what the relation commonly used in h.264 between the quantization
> > factor (NOT QP which has a log scale) and lambda is?
> > 
> > And to preempt the question about the values of A and B, they can be found
> > simply by comparing a RD based encoder (which selects scalefactors based on
> > the lamda values) to the 3gpp model, A and B should be selected so that
> > both encoders choose most similar scalefactors
> any papers reference aside mp3-tech.org would be good. 

i only have RD papers related to video coding ...


Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Thouse who are best at talking, realize last or never when they are wrong.
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