[x264-devel] Re: Scalability

[Alex Izvorski]

On Wed, 2007-02-28 at 15:49 -0700, Loren Merritt wrote:
> On Wed, 28 Feb 2007, Alex Izvorski wrote:
> > Thank you for some very interesting results.  Could you do a run with:
> >
> > x264 --bitrate=8000 --ref=1 --keyint=30 --scenecut=-1 --bframes=1
> > --no-b-adapt --threads ${NTHREADS} -o output.264 input_1920x1080_512.y4m
> >
> > and with threads up to 256 or 512?  I suspect that will scale much
> > better.  Thanks ;)
> 
> OK, I remembered a limiting factor: The motion estimation prepass
> (for b-adapt, scenecut, and ratecontrol) is singlethreaded. It runs
> concurrently with all the other threads, but only 1 thread is allocated to
> the prepass.
> If you disable those features (--qp 20 --no-b-adapt --scenecut -1) or if
> you run a 2nd pass (which doesn't do the prepass again), it should scale
> better.

Yes, that is what I was trying to do, I just didn't realize the
ratecontrol needs a prepass also ;)

> I would guess that Alex's command would scale worse than the original, 
> since Alex left in --bitrate (so a prepass is still needed), but increased 
> the speed of all the other options (so the prepass takes a larger 
> fraction of the total cpu-time).

Quite right.

Christian, could you change the options I sent to: 

x264 --qp=20 --ref=1 --keyint=30 --scenecut=-1 --bframes=1
--no-b-adapt --threads ${NTHREADS} -o output.264 input_1920x1080_512.y4m

Thanks.
--Alex


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