[Ffmpeg-devel] Fixed point arithmetic RealAudio G2 (cook) decoder

Ian Braithwaite ian
Wed Mar 7 16:51:13 CET 2007


I've modified ffmpeg's cook decoder to operate with fixed point.
I have an ARM based box I'm using as an audio media player, so now
it can stream radio from the BBC, too.

Regarding speed, the fixed point version runs about half the speed
of floating point on my Athlon. On the ARM, it runs about 25 times
faster than (soft) floating point, good enough for real time (25% load).
(I've used C's integer multiplication, I've not looked into assembler
 optimisations for specific CPU's.)

As regards quality, I've compared the fixed and floating point outputs
on a 46s sample. 95% of the output values are identical, the rest
differ by +-1.

Is there any interest in taking this code back into ffmpeg? I can
see in the archives that fixed point comes up occasionally, but it
doesn't seem to attract much attention.


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