I don’t understand how a 4K Blu-ray movie with 4x the pixel data can fit on a disc that’s only 2x a 1080 Blu-ray. They must compromise the bitrate? HDR must add overhead also?
The codec moved from h.264 to h.265, which is a big boost in efficiency, plus the extra pixels don't require as much information to describe as the original ones. 128mbit seems pretty good given that