[Libav-user] Chroma subsampling Implementation

[Michal Rapczynski]

Hello libav-list,

i have a question regarding the implementation of chromatic subsampling 
in FFMPEG and hope someone could give me a hand.

When encoding a video using x264 or x265 from e.g. RGB images or an 
YUV444 video to an YUV420 video what method is used to calculate the 
subsampled chroma values? Is some kind of mean average calculated for 
every block or is just one value used and the other three disregarded?

Thank you for your help

Michal