[tyranuus]

Cheers Desbreko, that might explain what I was noticing more obvious blocking in the dark scene, that's certainly worth bearing in mind if it'd resolve the issue as much as a lower CRF, but remain more efficient. Also, I guess if x264 is limiting the ref frames to 4 with level 4.1 there's not much benefit in the animation tag, if as Fluff says, it's main benefit is doubling the ref frames.

So in this case, do you believe it'd be better to use:
--preset slower --tune animation --level 4.1 --crf 16.5 --fps 24000/1001 --aq-strength 1.0 --psy-rd 0.8:0.1 -o <output.mkv> <input>

--preset slower--level 4.1 --crf 16.5 --fps 24000/1001 --aq-strength 1.0 --psy-rd 0.8:0.1 -o <output.mkv> <input>

OR

--preset slower --level 4.1 --crf 16.5 --fps 24000/1001 <output.mkv> <input>

Thanks all for the help!