[Ffmpeg-devel] Re: BUG: AC3 encode volume is low

Justin Ruggles jruggle
Mon Apr 10 19:55:30 CEST 2006


Hello,

Thanks for applying the patch.  I learned quite a lot trying to prove it
was correct :)

Benjamin Larsson wrote:
> Is the window generating code under LGPL?, it could be useful for the
> AAC decoder and it could be used to generate the window instead of the
> precalculated one.

I should have mentioned before that the window generating code was from
liba52, which is GPL...sorry.

I have just done some more research on the subject though, and I have
reworked the code.  Wikipedia was quite helpful in understanding what is
going on.

http://en.wikipedia.org/wiki/Kaiser_window
http://en.wikipedia.org/wiki/Bessel_function
http://en.wikipedia.org/wiki/Hypergeometric_series

There are now separate functions for the kaiser window and kbd window.
It is also now more generic (AAC uses different alphas and window sizes
than AC3).  The new code is LGPL, so you're free to use it in FFmpeg's
AAC decoder if you wish.

-Justin
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