That is stock footage of the ends of a film roll exposed to light during the loading process that is simply laid over the video with the add or screen blend mode applied. You can search for "film damage" stock footage and find something that would work from stock footage houses. You can fake your own with shape layers, blurs and opacity animations using the same add or screen blend mode. It's just much harder to get the film damage to look "real."
Here's what my google search turned up as the first link to stock footage. I have no relationship with this company and have never used their footage.
You could also just get your smart phone close to a lightbulb, make sure it's out of focus and then move it around.