It might be worthwhile giving other forks of the WMFVideo code a shot. @paul.houx has done a fair amount of work iirc, and his branch would be the first I’d give a shot just to see if anything changes.
I also recall @paul.houx taking a break from having anything to do with the apparent nightmare that is working with accelerated video decoding in Windows if the goal is to eventually get the output to an OpenGL texture. So if nothing seems to budge with WMFVideo there are other possible options to explore:
aaaaaand I just noticed you’ve commented on that thread, so you’re well aware of it 