1. A video encoding unit including a first data input arranged to receive a video stream with a plurality of image frames from a camera monitoring a scene, a second data input arranged to receive sensor data from a sensor unit detecting motion in a plurality of predetermined scene regions, a processing unit arranged to generate an overlay representing the sensor data and add the overlay to the image frames in the video stream, wherein the overlay has a plurality of overlay regions representing the scene regions, wherein the overlay includes a graphical element in those overlay regions which represent scene regions in which the sensor data indicates that motion was detected by the sensor unit.