Custom LUT for HDR grades in YouTube

[Cary Knoop]

Did anyone succeed in using a custom LUT for transforming HDR to SDR on YouTube?

All I get is that the LUT for SDR conversion is problematic.

 

[Tom Roper]

I did several. Most worked, then YouTube went broken, and now haven't uploaded YT videos for a while. But the process worked like this; put the SMPTE-2084 PQ HDR file on a new Resolve timeline in Resolve YRGB color managed space, then apply a 2084 to 709 lut. Create a node and make the SDR adjustments. What I don't remember is whether this was an input lut or output lut. I seem to remember it was an input lut, such that the trim pass would be making SDR adjustments to the 709 lutted copy. After making your adjustments, save a cube lut. Attach the cube lut to the mkv file with mkvmerge. This I did from the command line. There is another utility, mkvinfo or similar name that you use to confirm the attachment was made successfully, as well as all the other metadata. You can browse the YT FAQ Help topics, and several questions from Marty (The HDR Channel) mentioned that YT handling of the luts went broken, for some period I can't say how long. I know that mine were all working, and then the most recent attempt did not. I was emailing Marty about this, he was asking me to write YT to escalate the issue. So I think it ends up that YT generates an SDR copy, and applies your lut to the SDR copy. I was doing this around the Christmas holiday in 2016, so it's been more than a year!

 

[Cary Knoop]

Thanks Tom.

Things are working now, I am using H.264 in a mkv container and then add the custom LUT and the required tags. A custom LUT is almost mandatory to get a good fallback to SDR.
I remain to have problems using H.265 which works great for SDR content but remains an issue with HDR content.

My workflow for the custom LUT is to take the HDR version into Resolve (not color managed), apply a Rec709 to Rec2100 color transformation, color correct it and export the total result as a custom LUT.