A video signal coding system for network transmission includes a video output apparatus and a signal conversion apparatus. The video output apparatus includes a decoding unit decoding an video signal encoded by a coding method using a motion vector and a superimposing unit superimposing reference control information containing at least a motion vector on a blanking period of the video signal, and outputs the video signal with the reference control information superimposed. The signal conversion apparatus includes a separating unit separating the reference control information from the blanking period, an encoding unit encoding the video signal by the coding method using the motion vector, and a motion vector converting unit converting the motion vector in the reference control information into a motion vector corresponding to the coding method in the encoding unit, and the encoding is performed using the converted motion vector.