[FFmpeg-devel] Fixpoint FFT optimization, with MDCT and IMDCT wrappers for audio optimization

Mike Giacomelli giac2000
Mon Aug 13 17:02:24 CEST 2007

Sorry for the hotmail nonsense.  I will try my gmail account.  Hopefully it
will behave better.

>On Mon, Jul 30, 2007 at 10:33:16PM -0400, Marc Hoffman wrote:
> I will do it if it makes sense right now I don't see it being the most
> efficient. Lets get through the basic acceptance and when you and I
> decide to move forward we can talk about more efficient mechanisms for
> general machines. (I'm not going anywhere so even if you accept this
> we can change it in the future).
> The split radix is not the most efficient way to do things on the
> BlackFin machine. It has to do with all the extra pointer stuff you
> need to maintain. On other machines this is more efficient. Not to
> go into this too much anyways I agreed earlier to implement this for
> us (ffmpeg-devel) and I will just not right now. I really want to see
> if I/we can get one audio codec to work in fixEDpoint and achieve high
> quality I think this is what you/we really care about anyways.

Marc,  I've implemented a the ffmpeg wma decoder in fixed point for Rockbox
while you were discussing this.  Sadly I didn't see your mailings until
now.  The code is a huge mess, but quite functional on several portable mp3
players.  I converted the MDCT/FFT to fixed point in a very similar way as
above, and got very good results (typically 15 bits identical to the fp
version) and good playback (needs about 40MHz on my iPod).

Please feel free to take a look at the code:

Though once again, the code is extremely messy, and I'm still tracking down
a handful of remaining bugs.

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