[x264-devel] Trouble keeping 8 cores busy

Phil Rutschman philr at modsystems.com
Tue Jan 13 21:40:56 CET 2009

> In general, frametype/ratecontrol lookahead is not (yet) threaded.
> For maximum threading performance, use --no-b-adapt and --scenecut -1
> (disabled), but do note that x264 will still tend to cap out at under
> 8 cores when using very fast encoding settings.  Since the speed cost
> of lookahead for a given set of frametype decision settings is
> constant, x264 will be able to use more and more cores as you slow
> down the settings unrelated to lookahead.
> Also note that threading is limited by frame size.  You generally will
> not be able to get away with a value of (vertical height of
> image/number of threads) less than ~24 without B-frames, and less than
> ~16 with B-frames.
> Dark Shikari

Thanks for the information. Disabling b-adapt and scenecut detection did
boost utilization notably. 

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