P.S.: I don’t’ understand something though, isn’t the HDR metadata supposed to be there precisely to determine, frame by frame or scene by scene, what the picture is supposed to look like?
HDR10 does not have metadata. It’s just plain old HDR (Rec.2020 ST.2084), and nothing else.
Dolby Vision has metadata which contains information that trims down the the Rec.2020 ST.2084 (HDR) source to a Rec.709 Gamma 2.4 (SDR) output. But to my knowledge, that metadata from the disc is only readable on a TV.
You could import the Rec.2020 ST.2084 source into DaVinci Resolve and run it through Resolve’s Dolby Vision scan, and that will give you brand new SDR metadata which you could use to export an SDR video. However, it won’t have the nuances and custom adjustments that the colorist would have made for the original Dolby Vision pass.
I should also note, as a reminder, that HDR footage is similar to log camera footage – meaning, it has much more latitude to work with than SDR footage. So if you’re doing fan restorations, it’s better to NOT bake in an SDR conversion. It’s best to do color work within HDR, and then have your SDR conversion at the very end of the chain. That’s the workflow that this tutorial of mine hopefully illustrates.