The upcoming mimoLive version 5.6 will have a new feature in the PIP Window layer: You can add an image as a mask. Because the window defines the area where the image is drawn the mask only needs to be the size of the window. If you move the window the mask will follow. If you want to try it already please download mimoLive 5.6 beta 2 from here: https://boinx.com/connect/mimolive/versionhistory/5.6b2