x264: No subsampling vs. subsampling

Chroma subsampling is still used on Blu-Rays to save space. It's the same reason chroma subsampling has been used on every home video format. The average person won't see the difference, anyway, unless they have a player with a chroma upsampling bug.

I did a few limited tests with 4:2:2 source material (SVHS captures so very soft and very bad chroma already) using the lowest crf I thought gave a transparent 4:2:0 H.264. Using 4:2:2 with the same settings gave a noticeably larger file that wasn't noticeably higher quality. Trying to match the size (I never really got the same size) resulted in a lower quality file. I never messed with chroma-qp-offset. This is after deinterlacing, I could notice the difference (at least I thought I could) converting to 4:2:0 before deinterlacing. Edit: I don't think any of this is relevant to modern digital source videos, sorry. Ah good ol' analogue formats. :o

Come to think of it (after watching some 1080i50 videos) is probably the same thing with 50i -> deinterlacing(to 50p) and 50p (with a good encoder) at the same bitrate.

Note that for human faces HVS is very sensitive. The subsampling seems to me to be safer than possibly noticable color quantization, except for high bitrates... I may try some simulation TESTS with JPG subsampling modes saving to the same size.

I don't think you know what quantization (in terms of frequency-domain coding) actually means... If you're worried about the average color changing, that's quite unlikely to happen given the way DC coefficients are coded in H.264 and the way chroma QPs are calculated.