Image and track mattes in a superiour track both create an area of transparency in a video clip in a track below. Your choice in the Effect settings for the image matte are to use Luma or Alpha. I typically use Luma. Create an image (720 x 480) pure white (255,255,255). Add a pure black (0,0,0) shape to the image, export as a .gif. Premiere will use the black area to create the transparency, typically in Video 2, allowing Video 1 to show thru… Apply the track matte effect to Video 2, not the track matte in Video 3.