YCbCr 4:1:1

From MultimediaWiki

YCbCr 4:1:1 refers to a packed YCbCr format in which 4 pixels in a group of 4 consecutive pixels in a row is represented by one Y sample for each pixel but all 4 pixels share a single Cb sample and a single Cr sample.

(Note that YCbCr is often falsely mixed up with analog PAL's YUV.)