Yeah the "without visual impact" bit is a lie. People working in image / video compression are in denial about the noticeable quality drop with 4:2:0. 4:2:0 is

Yeah the "without visual impact" bit is a lie. People working in image / video compression are in denial about the noticeable quality drop with 4:2:0. 4:2:0 is extremely noticeable if your computer monitor gets into that mode. There are some major failure cases involving alternating single pixel width red / black lines. That caused issues with DVDs because the format also used interlaced frames, meaning things like red tail lights at night could end up looking awful. Luckily AFAIK they've given up on interlacing. I really think with modern tech they'd be better off trying to compress 4:4:4 instead of immediately throwing out a lot of colour information.