My understanding is that HDR video isn’t all that different from photography, but instead of photographing the scene more than once, they transfer the print more than once.

Now it’s still vaguely unclear what is being done, and there are no public tools for transferring or encoding in this format yet.

Many films have a digital intermediate (DI) that is approximately 2k (this includes post production work and effects). They then do some ‘magic’ to extract the brightest and darkest regions from the film and create an artificial 4k LAYER that they place on top of the 2k DI and re-color time to take advantage of the wider Rec.2020 colors.

Don’t get me wrong, there are true 4k films, but percentage-wise, not as many films as will be released as UHD. The process above allows them to call a film UHD, even though there is upscaling involved.

The important thing to realize is this is just 21st Century Colorization. Directors and cinematographers of today barely understand the technology right now, and certainly none of them who shot films prior to the last few years had any intention of their films looking like how UHD/HDR discs are being created.

I’ll watch new films intended for HDR, but applying the tech to older films is a travesty, just like colorizing black and white.

Btw, it should be mentioned the open tool of x265 is still immature and inferior to x264. A good alternative if you are doing your own 10-bit transfers is to use Hi10P. It’s less compatible with hardware devices, but is a mature portion of x264 that allows 10-bit color.