Quote:
Originally Posted by mp3dom
I was able to fix it a bit (the problem is still there, but less evident) adding a cetain amount of grain to the image, but this clearly is a workaround and not the right way to fix it, since the grain was not there in the source! Also, adding grain is not always enough, it depends by the scene itself and with totally flat sources, adding grain on selected scenes is a no-way... too much evident that there's something wrong.
The problem is triggered when using vbv, 1 slice or 4 slices doesn't make any difference, and the same apply to the use of a third pass or lowering the threads.
During and after the "hit" there's a big jump in QP values, I saw a difference of 14-15 on some cases and since the scene is exactly the same, it's clearly visible especially on gradients/shades, albeit the problem last for 1 second.
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Yeah, sounds like a fundamental rate control issue. Blu-ray uses a lot shorter GOPs than "normal" x264 scenarios, which limits the scope of --rc-lookahead, which could factor in. A real fix will require dev work.
A temp fix would probably entail reducing the initial peak, so the following valley doesn't need to go so low. Something like --qpmin 8 or --nr 500 might be worth trying. Hopefully lower values could work in practice.