A switch for switching video signals in a set top box between a first interface for connecting the set top box to a television, a second interface for connecting the set top box to a video playback device, and decoding circuitry for decoding a video stream, the set top box including a processor having a low power mode in which the decoding circuitry is inactive, the switch including detection circuitry arranged to detect, while the processor is in the low power mode, activity on a video input line of one of the first and second interfaces, and arranged to output an activation signal to switching circuitry in the switch to activate a loop through between the first and second interfaces when activity is detected.