Hi Charssay,

I understand you. I've just begun to play with VMix and have successfully overlaid a video with alpha transparency over the program video. To do so, I;

o created an RGB-Alpha Quicktime file
o imported that file as an input
o clicked the [1] Overlay button under the that input to overlay the graphic over the program output (similar to a downstream keyer.)

-or-

o import that file as an input
o included it as a Multi View layer in another input (thus overlaying it with the background)
o transitioned the multi-layer input into the program output

Best,

Michael