I have a timelapse with a static canyon in the foreground and the moving milky way in the background.

I want to mask out the canyon with a brighter/lower noise version I took afterwards.


At what point in the whole process should I do this? Is there a way to automate it? Having to mask hundreds of frames in PS is quite tedious. Thanks!

You could easily do this in After-Effects, or any other Video editing program, just be using two tracks. On the uppermost you put a still of the static frame with a transparent area, where you would like the moving part to show through.