[FFmpeg-user] slow performance with lut3d filter

Clément Bœsch u at pkh.me
Wed Feb 12 10:29:24 CET 2014

On Tue, Feb 11, 2014 at 11:20:43PM +0100, Clément Bœsch wrote:
> On Tue, Feb 11, 2014 at 02:11:43PM -0800, Elliott Balsley wrote:
> > I'm getting very slow performance with the lut3d filter.  Is this
> > normal, or is there some way to improve it?  This test encode runs at
> > 5fps, compared to the same operation without lut3d at 40fps.  CPU
> > usage is less than 10% during the whole encode.  I'm using a 12 core
> > Mac Pro.  Source footage is ProRes 4444 from Arri Alexa camera.
> > 
> Yes it's slow for several reasons:
> 1) it request rgb, so there is convert from yuv to rgb and back
> 2) lut3d is cpu only for now (no GPU accel)
> 3) lut3d has no SIMD
> 4) lut3d is not threaded
> Threading could probably be added. SIMD might not be worth the effort, but
> patches welcome. GPU can be interesting, patch welcome as well I suppose.
> Not much to do about the first point, except add some specific optims in
> swscale.
> Feel free to open a ticket, and eventually add a bounty. Or send some
> patches if you're a developer.

I just committed a small change to make it faster; I got a few more FPS,
you might want to try. Still no threading, SIMD & friends, that was a
trivial change. We can probably make it a bit more faster by removing one
if in the inner loop, but I'll do that later.


Clément B.
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