A CCTV multiplexer or Closed Circuit TeleVision Multiplexer allows more than on camera to be connected to the unit but only one output at a time is allowed through the unit. Most Digital Video Recorder or DVR units have this function built right in to the DVR. Another way to describe a multiplexer is by its function which is to combine various input signals and generate only one output signal. You can almost think of a CCTV Multiplexer as being similar to a computer router.
The backbone behind any good digital video security system is the surveillance DVR or Digital Video Recorder. It processes the video transmissions sent by the digital video cameras, controls the video cameras, stores the recorded surveillance video footage, and transmits the real-time and recorded video images to the monitor, the internet, or some other output device. In essence, the surveillance DVR is actually the brain of the security and surveillance digital video system.