[FFmpeg-cvslog] r12397 - trunk/libavcodec/ac3dec.c

[Justin Ruggles]

Rich Felker wrote:
> On Sun, Mar 09, 2008 at 06:05:19PM +0100, jbr wrote:
>> Author: jbr
>> Date: Sun Mar  9 18:05:19 2008
>> New Revision: 12397
>>
>> Log:
>> downmix before imdct unless different size transforms are used. about 20%
>> faster 5.1-to-stereo downmixing.
> 
> I don't understand what this 20% is measuring? Time spent in
> downmixing? That should be the same either way. The performance
> difference should mainly be in the number of IMDCTs (6 vs 2) and I
> suspect it makes a 50% or more difference to overall decoding time.

That is total decoding time.  It's actually 5 vs 2 since the IMDCT was
not done for the LFE channel when downmixing was used.  I gladly welcome
other peoples' benchmarks.

-Justin