Sounds to me like there are several users here ignoring the Crop and Transform tools. With them you can remove sides from your green screen footage, round the corners, place content wherever you want, etc.
Crop out Unwanted parts of the Video.
Use green screen to make things fly!
Crop Out Objects Or People!
We should be able to trim the area of the video an not only the length
I would like to create my overlays with different kind of masks. Round, square, heartshaped and so on.