Abstract: A system for transmitting coded digital video signals in a packet form through a signal line and a method of controlling the system. A transmission portion converts the digital video signals to a signal stream as a sequence of a plurality of packets each containing a predetermined sync code and a payload, and transmitting the signal stream. In case a fail of periodicity of the video signals is detected, a signal stream containing a packet into which a predetermined dummy signal not being the sync code is inserted into a position of sync code in a packet to be transmitted at that time and is transmitted. When receiving no sync code at a predetermined portion in the received packet, a reception portion executes an image reproduction process on the basis of the video signal data not depending on the packet containing the dummy signal and is so received.