I recently had a setup with four projectors, two projected on a screen blended pretty significantly (approx 50%) and two projected on the floor with the same aspect ratio and blend percentage. During parts of the show we brought in an HDMI feed from an iMac running Processing and a few other applications to incorporate some generative graphics into the show. My capture card is a Magewell Pro Capture HDMI. From time to time, we'd experience an issue where the captured image would appear in the non-blended areas of the raster but the blended areas on both the screen and floor were a hard black image. This would effect both the live feed media as well as any still imagery that was cued into the timeline. No media was visible in the blended areas. It seemed to happen most when the HDMI source was plugged in after the system was online, but I can't say that was consistent. Typically it could be solved by restarting the Display CPU, although a few times it took more than one reboot. I believe it was relatively stable during performances and that this happened mostly during the rehearsal process.
The specs on the computers are:
Watch*Cube by Show Sage
Intel Core i7-6700 CPU @3.40GHz
16.0 GB RAM
Windows 7 Professional Service Pack 1
AMD Fire Pro W4100
Pro Capture HDMI
I'd be very curious if anyone else has seen this and could explain why this happens. I found a workaround, but it's not one that I could implement during a live performance if needed.