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

mmh mmh
Wed Aug 15 17:57:20 CEST 2007

Mike Giacomelli writes:
 > 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:
 > http://svn.rockbox.org/viewvc.cgi/trunk/apps/codecs/libwma/
 > Though once again, the code is extremely messy, and I'm still tracking down
 > a handful of remaining bugs.


I will take a look at it, I guess its identical to the existing
reference FFT.  Maybe thats a better place to start, considering I had
to put this project aside for the rest of the month.  I think I will use
yours to start when I pick it up again.


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