For most players this appears to made no difference. But one case it fixes
is that with this metadata, on Youtube with SDR, 10bit PQ looks the same as
12bit PQ, where it was previously too desaturated.
10bit and 12bit HLG was already consistent without this metadata and there
appears to be no impact, though it remains inconsistent with PQ.
It seems good practice to be explicit about the mastering display regardless.
The way we get the max luminance is not ideal though. We get it from the
view transform name containing "HDR XXXX nits" as used in the Blender and
ACES configs. There is currently no way to query this information from
OpenColorIO.
In the future we can add a user control for this. For now if we can not
determine the max luminance this way, we don't write mastering display
metadata. The video player will then make some default assumption for tone
mapping, often 1000 nits.
Pull Request: https://projects.blender.org/blender/blender/pulls/144378
a599ce0908