Add light rays to a clip. The bright regions of each frame become the sources: they are smeared away from a chosen light position, faded along the way and screened over the picture. Because the sources come from the frame itself, a window that pans across the shot carries its beams with it.
Light position
Light X and Light Y place the source as a share of the frame. Match it to the real light and the rays follow the shadows already in the scene; put it off to one side for a stylised look. On a moving shot the light position is fixed in the frame while the sources move, which reads naturally when the light is at the frame’s edge.
Threshold and flicker
Only pixels brighter than the threshold cast light. Exposure drifts over a take, and a source near the cutoff pops in and out, which shows as flicker in the beams. Set the threshold with a margin on either side of the brightest region’s level, checking the darkest and brightest moments of the clip in the preview.
Length, fade and colour
Ray length is how far the smear reaches toward the light. Fade sets how fast it dims along the way, and intensity scales the finished light. The colour tints only the beams, since the blend is a screen and leaves the rest of the frame alone.
Cost
The smear runs at half resolution in two passes of 16 samples, which keeps a 720p frame around a third of a second on a laptop core. At source size on a 4K clip the export takes several times longer, so set the size before exporting a long clip.