Fading a video signal can’t be done simply by attenuating the composite signal, since the synchronization signal may drop below unacceptable level. Here a circuit to overcome the problem:
Most of video signals will works with this circuit, except for very noisy or distorted signals. The rest circuit is an LT1251 video fader (U2) configured to fade the signal ranging from the original level to black level. [Circuit schematic diagram source: Linear Technology Application Notes]
