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Analogue CCTV
Traditional CCTV systems are known as Analogue. This means that video signals are passed from the CCTV camera in a continuous electronic wave (similar to radio or television). These waves may be intercepted by a CCTV monitor to display live video footage from the camera and/or recorded on a video recorder (VCR). Many CCTV installations have more than one camera and use a multiplexor to channel each video signal in turn to a VCR or monitor. The main attribute of an Analogue system is that the video signal is continuous - requiring constant monitoring or recording and playback in order not to miss images of interest.VCR technology records the analogue video signal on a moving magnetic tape. The video signal can be recreated by playing back the tape, however the signal quality degrades in the process of recording. This degradation increases as the video tape is re-used even past the point when the playback signal is unusable.
A VCR can only record one video signal. To record multiple signals a multiplexor passes each video signal in turn to the VCR. This means the VCR is actually recording snippets of video from each camera in turn. These snippets must be replayed through the multiplexor which re-assembles the snippets from each camera. A single VCR cannot record and playback at the same time. A multiplexor that can record on one VCR and playback from a different VCR at the same time is known as Duplex.