I can beat that - a masked video with only 2 layers!
Using the (very simple but effective) plugin attached, apply a circle to any clip, set its colour to white, its background to black then set a blend mode of multiply at 0.5 opacity. Then twiddle with centre and radius as desired.
Before anyone asks, I don't have the skills or kit to make a mac version, nor do I have the skills to significantly change the functionality of the plugin. It's a simple circle - that's all.
