It is sometimes hard deciding on whether to specify a quad unit or a multiplexer on a CCTV proposal. A quick review of each will help you determine your needs. With a quad, what is being seen on the monitor is exactly what is being recorded. If the monitor is displaying in quad then the VCR is recording in quad, and therefore the tape playback will be in quad. Some quads have a feature that will allow the user to play back video that was recorded in quad and call up an individual quadrant to full screen.
Picture resolution is lost during the process and the picture quality is in the eye of the beholder.
For applications that rely heavily on taped documentation you should consider a multiplexer. These full-frame pictures are sent to the VCR for recording without being combined together or reduced in size. However, because the multiplexer only samples pictures from cameras in a system, it can not provide real-time display. In summary, multiplexers are better for applications that rely heavily on taped documentation while quads are better for applications that rely more heavily on live display monitoring and surveillance. One of the limitations of conventional video recording is that the maximum record time is limited to a few hours.