[FFmpeg-devel] [PATCH] activate ac3 decoder

Benjamin Larsson banan
Fri Aug 10 10:17:36 CEST 2007

Guillaume Poirier skrev:
> Hello,
> [...]
> You seem to be putting a very big focus on getting the FFT that has
> the fewest number of computations. Indeed, split-radix is the most
> efficient in terms of using the fewest number of add and mul.
> However, after reading some different papers on FFTs and googling
> around, I'm not that convinced. This paper:
> http://www.fftw.org/fftw-paper-icassp.pdf
> by FFTW people show that in practice, there are other things to take
> into account (e.g. CPU cache) than just the number of computations.
> There seem to be so many FFT libs out there that I wonder if we really
> need to write our own, except, of course if there aren't any decent
> that's LGPL-compatible.

Agree on that.

> Heck, if we didn't care about the license, Intel's IPP is clearly the
> best choice out there ;-)
> J/K
>> 2. implement djbfft support (this should be trivial considering that
>> liba52 needs something like 5 lines of code for it)
> According to the website djbfft uses a split-radix-2/4 FFT. This looks
> like what you are after isn't it?
> Why don't we just cannibalize the relevant parts of djbfft and make do
> without step 1 of your checklist (1. implement a plain C split radix fft)?
> I couldn't figure out what's the license of djbfft so I don't know if
> that's possible though :-(
> Guillaume

Don't forget KISS FFT. It's BSD (the good BSD) licenced.

Benjamin Larsson

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