[keithwinstein]

I don't think this is quite right. My understanding is that 4:2:2 chroma subsampling for Rec. 601 video (and the choice of sampling at 4x the chroma sub-carrier) came around in the days of 525/59.94 vs. 625/50 systems, before even the Japanese analog HDTV systems -- see my link above (https://tech.ebu.ch/docs/techreview/trev_304-rec601_wood.pdf).

[zinekeller]

Thank you for pointing this - I've checked engineering notes from that time and it was indeed mentioned (it was even mentioned in proto-D-MAC from 1981), I'll correct the post. I wonder though how I missed that, worse forgetting Rec. 601!