edit: Well, maybe not. An example file I have would need these parameters:
X265 Parameters:
hdr10=1
hdr10-opt=1
repeat-headers=1
colorprim=bt2020
range=limited
transfer=smpte2084
colormatrix=bt2020nc
master-display=G(13250,34500)B(7500,3000)R(34000,16000)WP(15635,16450)L(40000000,50)
max-cll=1655,117But when you try to add those manually to the x265 parameters the dialog box doesn't let you enter the last two lines properly. It interprets the commas as new-line characters and you get a bunch of new lines added that are nonsensical as a result, like this:
I can confirm this would indeed work, if SVP didn't mess up those commas. Because, if you reencode the transcoded SVP file again, using the exact same arguments, the HDR works correctly.
Therefore, to get HDR to work properly in SVP transcodes, you first need to transcode the files to some intermediate format (without or with incorrect HDR tags), and then transcode them again using the correct HDR arguments. So, it's possible, but it seems like a really silly bug in SVP.
Correction: This double-encoding approach apparently does not actually work correctly... but it does seem to be a part of the solution, as far as I can tell, so perhaps with some additional steps this might work.