Like what James says above.
Most likely the flashing that you’re seeing is a result of the exposure time the video was captured at. Say the shutter collects light for 1/100 of a second, and the LED’s refresh rate was 50 cycles/second. Then, the amount of light a video frame collects would depend heavily on whether it is collecting light during the the “light” or “dark” part of the LED’s cycle. This is the flashing that you’re seeing. I get this in just about all of my videos when I’m following someone that has an LED brake light.
Hope this help you out Don, look forward to meeting you.