I've had that happen to my videos too, I think it was with my Canon 60D, but could have been with my 7D. Usually happens when I'm zooming with my 10-22mm lens and usually indoors. It's like the aperture jumps open then back again in my case but looks the same as yours with a blip of over exposure. I figured it was the aperture trying to find it's setting, since it's a variable aperture lens, or perhaps some kind of electrical interference.