It’s pretty easy to verify: create a uniform white png and convert it to yuv420p h264 via ffmpeg: ffmpeg -i input.png -pix_fmt yuv420p movie.mp4 Open in VLC o

It’s pretty easy to verify: create a uniform white png and convert it to yuv420p h264 via ffmpeg: ffmpeg -i input.png -pix_fmt yuv420p movie.mp4 Open in VLC or your favourite player and take a screenshot. Now check with a color picker whether you have white as 255 or 235. Update: checked with VLC and QuickTime Player, both handled it correctly and displayed white as 255.