[paddington]

that would be easy... a slightly-higher freq than visible light would do the trick. The camera's CCD would still see it. They could just fire a wall of LEDs in the IR spectrum from around the stage and behind to make the video unwatchable.

Of course, then they can't tape it themselves, either, unless they have cams with some special filtering mech to hide the range from the CCD.

To test, turn on the cam on your mobile phone, then fire your TV remote into it as you press a button on the remote. You'll see the infrared light flash on your phone's screen... but your eye doesn't detect those frequencies.