It doesn’t have to be over keyed video. This technique is an a lot of graphics in the last 2 years. I think the best way is using Knoll Lens Flare and program it without the lens artifacts so it’s just simple washes with some rays here and there coming out. Then just SCREEN transfer them over the top.
Or with just AE, Generate a solid with the RAMP effect set to radial. Create a white area graduating out to black. SCREEN this over the video and mess with the scale and opacity.
Also, sometimes people do it as a larger wash of color. Like create a 4 color gradient and set the colors to like sunset hues with some white tones here and there and try different transfer modes of this over your video. Like Hard Light, Soft light, etc.. Then tweak the opacity to taste. This helps gives it that painterly, watercolory vibe.
Chris Smith
https://www.sugarfilmproduction.com