[FFmpeg-cvslog] r12284 - trunk/libavcodec/ac3dec.c

[Justin Ruggles]

Justin Ruggles wrote:
> Diego Biurrun wrote:
>> On Fri, Feb 29, 2008 at 11:48:04PM -0500, Justin Ruggles wrote:
>>> jbr wrote:
>>>> Log:
>>>> Use 24-bit fixed-point transform coefficients until just before MDCT. This
>>>> gives 7% faster decoding on average.
>>> And obviously a fixed-point MDCT would be even better so we wouldn't
>>> have to convert to float just for the MDCT then back to fixed for 16-bit
>>> output.  Then we could also change the downmixing and dynamic range
>>> scaling to fixed-point as well.
>> This obviously brings up the standard question: How well do we perform
>> compared to liba52 now?  Is it time to remove liba52 support from
>> FFmpeg?
> 
> So obviously the biggest area for improvement is in the downmixing.
> Today, I am planning on trying to move the conversion to int16 to before
> downmixing and doing the downmix in fixed-point.  I'm not sure if it
> will be faster though until I test it out.

Well, that didn't help.  Having to convert all channels to int16 offset
the speed gain from fixed-point downmixing.  Although I did manage to
find a small speed-up in the process.

-Justin