SOLVED: M1 Imac Screen Flashing

I use two M1 iMacs. TouchDesigner is on one. It sends a video hdmi to Blackmagic where that stream is synced with audio from a mixing board then the two are sent usb to second M1 iMac where they are processed by ecamm live, proprietary a livestreaming software. Touch designer receives a video stream from a Blackmagic switcher which is hooked up to four Sony 6400 Alfa cameras. The Sony’s are sending a 30p 50 m video to Touchdesigner. Apple display settings change automatically depening on the plugged in dperipherals. TouchDesigenr is sending one an hdmi stream to the Blackmagic Design device (web presenter). I’m experiencinh screen flashing periodically only when using touchdesigner. This flashing causes a brief interruption in the signal to the other commuter which is the one with ecamm live. I thought It might be a frame rate issue. TouchDesigner is 60fps, the BlackMagic is 60 fps and the cameras aRe 30p. I tried 60p on the cameras which only made the situation worse. With that setting. the iMac screen not only flashed but also jumped in and out of resolution. My BlackMagic design is sending out an hd1920 by 1080. If there is something on the forum aobut this, it didn’t come up in my search. If there is, I apologize. Please advise.

Sorry, could you clarify when the screen starts flashing, when which device is connected? And which screen, the built-in iMac screen or the Blackmagic screen output?

Please report macOS version and build number of TouchDesigner. Are you running macOS 13.2?

Sorry for any confusion
THe screen flashes when Touchdesigner is active and all the perferials are connected. THe built in iMac screen flashes. If TouchDesigner is in perform mode full screen a momentary black out occurs and that lapse is ent by htmi to the other iMac which causes ecamm live to lose signal for a moment. ecamm is a live stream program that I’m sending the TouchDesigner hdmi output to.

Ben, Currenly it has stopped flashing. I would not have guessed this but this may be the cause.
I have three cameras, Sony 6400s running hdum to a Blackmagic Design switcher and then into the computer running TouchDesigner. So I bought from B and H these little devices that suspend the micro hdmi chord from the cameras so that no matter how I move the cameras or stretch the cables the micro cables to the camera ports are stable. Since I installed them the problem has stopped. It may be that ther was signal dropouts that affected the behavior of the Mac ports. If this situation changes, I will come back to the forum but otherwise, I’m greatly relieved. Thank you for reading my entry. Grateful to you and all the other TD community.

There was one setting change as well . I updated display settings in System Stettings on the IMac so that the main dispay is The Built -in Display and the secondary display hs BMD HDMI (Black Magic Design HDMI).

I’m leaning towards thinking it was the connectors or cable connection. Those micro HDMI are the worst format of HDMI yet, very difficult to get a good seating.
Thanks for letting us know how you solved it.