[PD] [GEM] Using masks with videos

[Armindo Dias]

I've tried the MaskDancer example and i would like to aply that to video. I
want to have a video as the source pix and then another video as the mask
piece. I tried to do this but all i gor was an empty image... is it possible
to do masking with videos? And videos and images? And finally, do the two
sources need to have the same size (like 400x300)?