How can I reduce a bright flashlight from washing out my camera footage?

There's not much you can do to prevent a bright light pointed at your camera from causing lens flare that obscures the scene. But there are some things that can sometimes help.

The main thing to do is simply try to prevent the light from getting into the camera in the first place:

• If you're shooting with a long lens, make sure to use a good lens hood. It won't stop bright lights in the scene you're shooting from blinding your camera, but it can prevent someone outside the scene from interfering with your photography. And in some cases you may be able to turn your camera away from the bright light and still at least capture what's happening nearby.

• If you don't have a lens hood (e.g. you're shooting with a cell phone), just putting your hand (or a piece of paper, or whatever) between the light and the camera to shade it can help a lot.

• Even if the light source is inside the scene you're shooting (and you can't or don't want to turn the camera away from it), just blocking it e.g. with your fingertip can eliminate or at least dramatically reduce the flaring. This is one of the rare cases where you may want your finger in the picture!

• Of course, if there happens to be a convenient signpost or other obstacle that you can maneuver to be between the light and your camera, that can work even better than your finger. I've used this technique myself e.g. to shoot halos and other atmospheric phenomena near the sun, as in this example image from an earlier answer where I used a pedestrian crossing sign to block the sun: