A video signal is serially enclosed for transmission in PCM form during synchronizing level intervals and encoded in a run length limited NRZ form during non-synchronizing level intervals, each PCM word being selected from minimum and maximum disallowed states of the NRZ code. In a decoder, a first detector responds only to the presence of the PCM code for synchronizing a second detector with response to both the NRZ and PCM coded portions of the encoded video signal to provide a decoded video output signal whereby the PCM portion of the signal conveys both decoder timing information and information as to a specific level of the video signal.