Methods and apparatus, including computer program products, for processing a stream of image frames captured by a camera system. When an image frame from the stream of image frames is dropped, a current camera movement is determined. A substitute image frame for the dropped image frame is generated. The substitute image frame comprises a reference to a previous image frame and includes one or more motion vectors estimated solely based on the determined current camera movement. Remaining image frames in the stream of image frames are encoded and the substitute image frame is inserted at the place of the dropped image frame in the stream of encoded image frames.