How to change static material to a video gradually?

So here is the issue, I have a wall (static mesh) and I wish to enter a trigger volume (or trigger box, whatever is best for it) and have the material on the wall to change to a video material with sound. I can do this already, what I can’t is to make it stop when I exit the trigger volume AND to change it gradually, so it looks like the original material is blending or, fading away to turn into the video and vice-versa. At the moment this material swap happens instantly, which I don’t like :D, please help me!