Source was 4K, downsampled to 1080p. These are the basic parameters that I've set:
Code:
--input-depth 16
--dither
--profile main10
--min-keyint 5
--keyint 480
--merange 44
--splitrd-skip
--preset veryslow
--rc-lookahead 60
--deblock -2:-2
--no-strong-intra-smoothing
--no-sao
--qcomp 0.8
--aq-mode 3
--aq-strength 0.8
--ctu 64
--max-tu-size 32
--rdpenalty 1
--qg-size 16
--tu-inter-depth 4
--tu-intra-depth 4
--limit-tu 4
--limit-refs 3
--max-merge 2
--rd-refine
--ref 6
--bframes 10
--crf 19
I've then also tested ctu 32 with max-tu-size 32 or 16.
In the 1080p encode, the bitrate is as follows:
CTU 64 / TU 32 - 15078 kbps
CTU 32 / TU 32 - 14608 kbps
CTU 32 / TU 16 - 14472 kbps
Of these, CTU 32 / TU 32 resembles the original the most. It's interesting that setting TU 16 also causes distortion in the same areas as CTU 64 / TU 32. I checked areas like eyes, hair etc. which have easily some sort of distortion because there are many fine lines and things that can be compared quite easily.
I've just started testing what CRF value is visually enough for 1080p so the final bitrate will probably be lower than what I got from my tests. I'd estimate CRF 20-21 would be the final value.