Deblock problem

[cqustlym]

The source is a very grain BlueRay with a high bit rate(37.5Mb/s). There are a few dark scene has block problem so I used filter f3kdb to deblock and zoned those frames with lower crf. But there are new block generate when do the encode. I tried adjusted lower crf but the effect was not good. How can I handle the new block problem?

[Emulgator]

You may lower deadzones, restrict ipratio, pbratio

--level 4.1 --bluray-compat --nal-hrd vbr --aud --keyint <your parameters here> --min-keyint 2 --open-gop --bframes 3 --ref 3 --slices 4 --qpmax 48 --qpstep 4 --ipratio 1.2 --pbratio 1.1 --deadzone-intra 0 --deadzone-inter 0 --vbv-bufsize 30000 --vbv-maxrate 40000 --pic-struct --deblock -1:-1 --weightp 0 --me umh --merange 32 --subme 10 --trellis 2 --psy-rd 1.0:0.15 --videoformat <your parameters here> --colorprim bt709 --transfer bt709 --colormatrix bt709 --sar <your parameters here> --output-csp i420

[FranceBB]

Originally Posted by cqustlym

I used filter f3kdb to deblock

You used what? xD
f3kdb is a debanding filter, "db" at the end stands for "Debanding" not "Deblocking" XD

On a second though, strong debanding might even try to get a smooth gradient and identifies the differences between macroblocks as an error and therefore fixes blocking? Who knows... Still, you're better off with a real deblocking filter. The reason why I'm saying this is that f3kdb will introduce grain to fight banding, hence making the source more difficult to encode for x264.

Try with Deblock_QED or Unblock and see what happens, otherwise try to lower the amount of grain introduced by f3kdb in the parameters and see if it helps x264.
Other than that, follow Emulgator's suggestion for x264.

[benwaggoner]

With 8-bit SDR, blocking and banding do go hand-in-hand in low luma.

I'd try --aq-mode 3 for these scenes, which lowers QP in dark regions. It might help.