alpha channel or blending mode
Hello. I'm from Russia. I use Proshow every day. thinking about your product. He's attractive. But there are questions. If working with an alpha channel or something similar as in editing systems, for example, the Screen blending mode, to remove the black background.
It sounds like the feature you're looking for is "Chroma Keying", available form the "Adjustments" tab on the right-hand side of the program once you have the layer in question selected.
It sounds like you're using a video file that already includes transparency through an alpha channel. Photopia does not currently support alpha channel transparency from video files, which I believe explains what you're seeing. This is a feature we do plan to support in the future.