Can't tell if prores4444XQ is any different than prores4444 in ffmpeg 4.1 Using ffmpeg 4.1 and prores_ks codec.  I've encoded various clips into 4444 and 4444XQ.  All play and look fine but when I try to use -pix_fmt yuv444p16le for 4444XQ I get the warning:

Incompatible pixel format 'yuv444p16le' for codec 'prores_ks', auto-selecting format 'yuv444p10le'


My 4444XQ files are bigger than my 4444 files so there is an increase in bit rate.  But I was under the impression than 4444XQ supported 12bit color while 4444 only supports 10bit color.  There is no 12bit pix_fmt so I just assumed it would take 16 and do the down convert.  Maybe this is a limitation of the current ffmpeg builds and prores_ks needs to either do its own up/down bit depth conversion and/or ffmpeg needs a 12bit pix_fmt?
FFmpeg does have 12 bit pixel formats but the prores_ks encoder is limited to 10 bits. The 4444XQ profile features higher bitrates. Open a ticket at trac.ffmpeg,org, if you like.