Abstract: A system for overlaying a computer generated video signal on an NTSC video signal includes horizontal and vertical pulse processor circuits for generating a horizontal start signal and a vertical reset signal, respectively, in accordance with NTSC standards, and a clocking system for receiving the vertical reset signal and the horizontal start signal and for generating control signals to control the read out of video data from the video generator of a computer so that it is read out at an NTSC rate. The system further includes a video insert keyer circuit for combining the NTSC video signal and the computer generated video signal and for generating a composite video signal for transmission to a monitor or standard television.