The industry is currently starting to use MPEG-4 compressed digital video for surveillance applications. The transition from analog to digital video raises difficulties for using surveillance video in court. Since it is fairly easy to make hard-to-detect modifications to the video stream captured by the cameras, e.g. mask out a specific event or person, a system for proving authenticity and integrity of video streams is needed. This paper presents such a system based on digital signatures embedded in the video stream. Our concept provides a means for proving authenticity and integrity of MPEG-4 digital video streams, while leaving compatibility with standard media players untouched.