Roto Brush masking in After Effects, just a first attempt.

It’s got very ‘wriggly’ edges, not at all what I would like to have.

I will next look at using the pen tool to create a mask as I’m very familiar with this type of masking technique in Illustrator, but, I need to re-check the original film as it seems to be twice as slow as it should, so the framerate might need correcting…