A frame processor for preparing a stream of video frames for encoding, the frame processor being arranged to receive a video frame having first pixel dimensions representing the number of pixels along each dimension of the video frame, and comprising: a rescaling filter configured to rescale the received video frame such that one or both of the first pixel dimensions are no greater than respective predetermined pixel dimension(s) and the aspect ratio of the received video frame is maintained; and a frame generator configured to: embed the rescaled video frame within an output video frame having the predetermined pixel dimensions; and mark pixels of the output video frame outside the bounds of the rescaled video frame as inactive; the frame processor being arranged to provide the output video frame to a video encoder.