Non-roto subject isolation based on moving/changing pixels?

Greetings,
I have my static tripod clip where there only thing moving are the two talents but the background is completely static.

Is there any combination of nodes that would allow me to achieve some talent/subject isolation based on what’s detected as movement in a clip versus what’s static, similar to how motion blur in BorisFX can detect what’s moving in the clip and what’s static and then add a blur to the moving objects only? I’m thinking if there was a node/s similar to zMatte, but with a sensitivity for movement instead of luminance, hue, etc, and then I could just lower the range until the moving objects have some isolation. Is there any way I might be able to do this presently?

Thanks for any help on this!!

You can try making a “difference key” with a clean static frame without the talent and blended over the top with a difference blending mode, and then color correct that into a matte, but that’s one of those things where it either works OK, or looks like garbage. Difference keys are something you can get away with for things like rain in a shot, but not so great for talent. They just don’t look good in the final comp.

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Got it, thanks for the info Mary. In my case the Difference Matte didn’t work out, too many multicolored artifacts around the subjects, so just gonna focus on a better roto.

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That’s not surprising, if difference keys were a magic bullet everyone would just never do roto again. Alas. We do not live in that world.

Haha yes good point!!