Buffering a CVBS signal

I need a simple way of buffering a composite (CVBS) signal. Preferably, I would like to use commodity components, like op amps or bipolar transistors. My problem is at the moment, my on screen display project modifies a video signal by superimposing another video signal but it ends up re-synchronising to its own video signal, which causes it to wobble across the display.

Thanks.