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Creating a mask.
Hi all,
As indicated by the topic name, I need some help creating a mask.
As you can see in the background of this image, there are what is intended to be siren lights.

There weren’t any siren lights on set so it was done by having someone switch two lights with a red and a blue gel on and off. Unfortunately, I only have a small period of the shot where the switching between the lights is consistent enough and not erratic. So to keep the shot on for as long as we want it, what I think I need to do is mask that part of it and layer it on top of the rest of the shot.
If someone can direct me on how to do that or possibly recommend a better solution, that would be great.
Thanks in advanced.