I think you are referring to how they "strobe" in a video. This has something to do with the light frequency and the speed of the video. They appear to flash while in reality they aren't. If you are talking about something different I haven't heard of any DRL's that flash/strobe on their own.
Yep. Definitely the frequency of the light reacting with the frame rate of the video. It's similar to how the spokes of a car wheel look funny when cars are moving in movies (particularly older films). I also see the effect when I view the TB (and LED accents on many other cars) through the rear view "mirror" of my other car since it is actually a HD screen displaying a rear camera view.