vMix support just came back with the following regarding the Decklink 8K Pro.
Unfortunately, the Decklink 8K Pro is configured a little differently internally than other Decklink cards and in our testing did not behave as expected for Key + Fill Output and so we do not recommend it for that and why it is not listed in our documentation for Key + Fill support
This concludes that in vMix the DeckLink 4K Extreme 12G is the only card that can output 4k 60 key + fill (1 channel) the Decklink 8K Pro is not supported.
This brings us back to my original question, is CasparCG/ Decklink 8K Pro capable of outputting 2 channels key + fill 2160 60hz (on a single Decklink card
@Julusian I just found the following (older) thread:Decklink 8k pro - #19 by Andrea
Here @Andrea states
I have a DeckLink 8k Pro fully functional, double channel fill+key
for me the trick was in the blackmagic settings: 1ºin+2ºout and 3ºin+4ºout
in this way the f+k are linked together and perfectly in sync
(external keyer)
I tried only in 1080@50i, I don’t have any way to test higher resolution at the moment
That might help with your sync issues?
Seems like no one has tried @Andrea’s working config file for two key and fills in 2160p/i5000
This is exavly what i would like to do, but i do not have the 8k card yet.