Thanks for the feature request. The trickiest part is getting both videos to synchronize, and making sure the performance is acceptable. I'll have to do some research and testing to see if it's feasible. Packing the alpha into the same video is much easier and probably more performant, since only one video needs to be decoded. You can also create an hsp file with the correct alpha mask settings and distribute it with the video, and the correct settings will automatically be loaded when the user plays the video.