...
Conclusion:
FFMPEG seems to indeed process in 8 bit and ProRes4444 in Resolve is worth the extra bandwidth/bitrate.
Hi! Thanks for studying this topic.
I made a quick test input file covering the full range of 10bit input values, and encoding that with ffmpeg, then decoding back to rgb48 didn't show any obvious 2 bit quantising (though values do get changed due to the reduced value space). So I don't think your conclusion about the 8 bit conversion is correct.
Here's something else to try. The current default encoding uses the "-q:v 4" param, which changes the encoder to fixed qscale mode. Remove that argument, and instead add "-bits_per_mb 8000". Have another go with your test file and let us know in case that looks any better than the default.
You can also try, e.g. "-q:v 2" or "-q:v 0". All those settings should affect the final bitrate (and hence quality)
(The main reason to use the fixed qscale is that it encodes much faster, but if it turns out to be causing poor quality that will have to change!)