Sensing Jitter signal presence in GL chain for control of non-Jitter objects?

Hi,

Recommendations please!

The short version: I'm looking for the simplest and computationally cheapest non-jit.matrix way to sense whether a video signal is present at arbitrary points in a chain of GL slabs, so I can toggle non-Jitter objects accord to whether video signal is present or not.

The longer version: I have a SLEW of GL shaders switched in and out of a chain via matrixctrl + router (via send/receive objects). The parameters on each shader can be modulated by subpatchers containing MSP objects like LFOs. To save cycles, I need to be able to toggle mute~ for the modulation subpatchers according to whether or not the associated shader is switched in/out of the signal chain. I can certainly do this the hard way by hardwiring logic for each circumstance off of the matrixctrl. But it seems there should be a way to just sense if there's a video signal at the receive object that ties to each shader, and use that info to toggle the associated mute~ objects. Theoretically a video gate with binary output. Since this is Jitter video, straight numbers and math don't work directly. My only matrix is at the head of the chain, so I don't want to introduce any. I can't quite grasp whether jit.change would provide a solution in the middle of a GL chain... and how to get binary/numeric output? jit.op has some gating properties, but doesn't seem to provide for a binary/numberic output. jit.fps doesn't seem to provide binary/numeric output. The closest I've gotten (conceptually) is using jit.3m to derive numbers and then do some kind of numeric differencing/gating. I feel like I'm missing some infinitely simpler method, but am now officially to close to the problem. :(

Any love is appreciated! Thanks!

Jeff