OK - my intention would seem very easy to achieve, but I have completely failed to manage it!
Basically, I have a rotated video placed in timeline, which I simply want to overlay like a sheet of acetate, on top of the rest of the video. You can see it dropped in timeline here, with pan/crop shown.
Problem is, When I change the layer to "Multiply", I get exactly the effect I want BUT it has black all around everywhere but the video. What I really want to do is something akin to Photoshop's "fill behind". I've tried putting a white layer underneat, experimenting with parent/child and so on, but got nowhere.
Any ideas? I have achieved exactly this in a layer beneath (you can see it in first screenshot) but this was not a problem because the footage completely filled the frame.
Thanks for looking at this!