If its a just a couple of 2D textures then a Blender node might be an answer. Attached the two images to the blender node and then animate the "Blending" parameter. Blender nodes could be cascaded to support more than two but it starts to get complicated.

There is also a movie node that allows AVI to be imported with a frame_number input which possibly could be driven by an animated math node but never tried it.