[FFmpeg-devel] [PATCH] Move Kaiser-Bessel Derived window to mdct.c

Robert Swain robert.swain
Thu Jan 10 19:55:26 CET 2008


On 10/01/2008, Michael Niedermayer <michaelni at gmx.at> wrote:
> On Thu, Jan 10, 2008 at 04:38:16PM +0000, Robert Swain wrote:
> > The SoC AAC code uses a slightly more flexible version (variable
> > alpha, window size, iterations) of the Kaiser-Bessel Derived window
> > used in libavcodec/ac3dec.c. It is desirable to have the code shared
> > between ac3dec.c and aac.c rather than duplicated. I extended the
> > capability of the code in ac3dec.c and moved it to mdct.c. Please find
> > a patch for this attached.
> moving the code and functional changes must be seperate

OK, I will post more patches for this later this evening.

> And IIRC the num of iterations are just a matter of how good the
> approximation should be, what does AAC say about the ierations?

I think you're right but, from looking at the AAC spec (page 162 of
sp04), all I can see is a sum from 0 to inf in the zeroth order first
kind bessel function I0. I've looked around a bit but unless I'm
missing something, it doesn't say anything about the suggested number
of iterations to use. Maxim used 50 in aac.c, Justin used 100 in


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