[FFmpeg-devel] MDCT and AC3 encoder

Justin Ruggles justinruggles
Sun Oct 28 00:59:31 CEST 2007

Benjamin Larsson wrote:
> Fabrice Bellard wrote:
>> Regarding the AC3 encoder and the MDCT, I had a plan in the past to move 
>> the integer FFT and MDCT to their own files so that they can be easily 
>> reused.
>> Another task would be to modify the AC3 encoder so that it can 
>> alternatively use the floating point MDCT. Does someone have similar plans ?
>> Regards,
>> Fabrice.
> Justin Ruggles has done some AC3 work with his aften AC3 encoder lib. 
> And Marc Hoffman did some initial work for a fixed point frame work. It 
> has stalled though. The cook decoder has code that should make it easy 
> to use in fixed point mode as soon as there is a good fixed point mdct.
> MvH
> Benjamin Larsson

Right now the whole encoder uses fixed-point, not just the MDCT.  When I 
started Aften, I used the FFmpeg AC3 encoder, but made it all floating 
point.  I think the hard part would be making the FFmpeg AC3 encoder use 
either one.  I would definitely need some help since I've never done 
anything like that before.

I guess one way I could start would be to make a patch to convert the 
existing encoder to floating-point.  Then someone else might be able to 
see how best to make it use either fixed or floating point.

What do you think?


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