Change clip rect to custom shape

Hello,

sorry for another problem that is bugging me. lol

To make it short; is it possible to make the edges of a clip more "smoother"
or even display the clip elliptic, in a bubble or something similar?

The question more specified; How can I change the shape of a clip (by not being bound to a rect) ?

either use the vignette effect or use alpha shapes and composite with a black color clip.

Another way could be using the wipe file in the composite transition.