[x264-devel] x264 taking longer to encode static scenes (than scenes with movements)

Thu Sep 3 21:02:24 CEST 2015

Hi,
I'm using x264 for live video streaming and I've noticed that the thread
responsible for encoding uses 
more cpu (around 50% more with 1920x1080) when the video stream is frozen
(i.e.: camera is sending the same frame over an over again) or when I make
it encode the same image over and over again.

This seems somewhat counter intuitive to me, as I would expect x264 to use
more processing power when encoding complex scenes other then static ones.

I created a github gist based on the example.c encoder bundled in x264's
source code and tested encoding times with it. (You can find it here:
https://gist.github.com/danilogr/ab4976ff4e0831ab274b)

Average encoding time for the static scene is ~38% bigger than for a scene
with movements. (You can find my test case and also the output from my test
encoder on the link above).

I've also noticed that by setting "
scenecut=0, subme=0, trellis=0 and me=dia" I can get rid of this problem

 but with some quality

 decrease. (Not really noticeable in the test case provided).

Could anyone, please, shed some light on the reasons for this odd
behavior? 
Also, what can be done in order to avoid this situation without a major
decrease in quality?

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