[FFmpeg-devel] [TeX] DCA subband transform

Michael Niedermayer michaelni
Sun Sep 7 14:58:29 CEST 2008

On Sun, Sep 07, 2008 at 06:26:53PM +0600, Alexander E. Patrakov wrote:
> Hello,
> recently there was a discussion whether the DCA subband transform is a
> windowed MDCT or something else. The attached TeX file contains the proof
> that the original obfuscated transform is in fact, up to a constant factor,
> a pseudo-QMF cosine modulation ?lter bank combined with the sign ?ip of
> subband inputs whose number is congruent to 1 or 2 modulo 4.

It would be more interresting to know if every "pseudo"QMF is a windowed *DCT
and if every windowed *DCT is a "pseudo"QMF

> I will use this math in order to write a higher-level simplification of the
> transform code, in particular, I will remove the "noidea" history buffer.

you can just look at our mp2 decoder that implements the same summation 
without the extra buffer.

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Complexity theory is the science of finding the exact solution to an
approximation. Benchmarking OTOH is finding an approximation of the exact
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