I have burned the edges to frame the video and make the beginning look like a dream land. To do this, I created a circle using the video effects/generate tool and adjusted the ratio which changes the size of the shape.  Feathering the layer blends the circle into the image to make it look more subtle. I inverted the circle so inside the circle was blank and then changed the blending mode to normal. When the scene darkens, I edited the circle to give the image a black edge.