You probably cannot.
A cube captures 6 areas. The maximum texture size is 8k. Each face is limited to 2k if you have a regular cube unwrap.
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I don’t know how the arrangment of faces actually is, but even then its not really possible to get more than 3k.
OR
as set-ups leave you with the same surface area to cover.
It allows for more than the other setup. But its still lited to 8k/3
You could make a cube cature yourself with 6 different captures off a screencapture2d at up to 8k res each.
So long as you keep and stream the files in as separate things it should be OK.
Even if performance will be very low, I’m assuming this is to cook something in engine and not to be used at runtime.
I never really used one, but I’d also be surprised (ok its unreal, no it wouldn’t surprise me one bit) if the cube cature could not be set up to use VT and do the same thing with nearly unlimited per face resolution…