Unfortunately, there is no such creature available at this time... there are multiplexers that will play back in quad or full screen or even better (up to sixteen images on the screen at once). But there is no multiplexer that can play back images faster than real time.
The major problem is in the basic nature of the beast.... Since a multiplexer is (in general terms) nothing but a high speed switcher, it is merely switching between cameras at extremely fast rates of speed. This is also referred to frame grabbing since the unit is basically grabbing individual pictures from each camera in it's sequence.
For each picture that the multiplexer grabs, it lays down a digital code assigning the picture or frame to the camera that it came from. During playback, the de-multiplexer (usually a built in part of the multiplexer) looks for the associated code for each camera's frame or picture. The end result is that if you only want to view camera one, then you only see camera one. If you only want camera two, you see only camera two.
The problem comes in when you put the tape into any play mode that is faster than real time or thirty pictures per second. The de-multiplexer (demux) unit cannot read the digitally coded information fast enough and so the end result is a playback that looks like a total mess of all the cameras superimposed on each other.
At the end of the day, the only way to have the best of both worlds at this point is to look into the new disk or CD recorders and see if they fit your needs. These units allow you to mark or trigger events with total recall. I'm not sure if there is anything here that you can use, but it is the wave of the future and may be what your client is looking for.
Let me know if there is anything else that I can help you with and if you don't have a serious problem with it... I am in your service.
