Closed-circuit television (CCTV) systems use analog cameras to produce images or recordings for surveillance purposes, and can be either video cameras, or digital stills cameras.
Analog cameras can record straight to a video tape recorder which are able to record analogue signals as pictures. If the analogue signals are recorded to tape, then the tape must run at a very slow speed in order to operate continuously. This is because in order to allow a three-hour tape to run for 24 hours, it must be set to run on a time lapse basis which is usually about four frames a second. In one second, the camera scene can change dramatically. A person for example can have walked a distance of 1 meter, and therefore if the distance is divided into four parts, i.e. four frames or “snapshots” in time, then each frame invariably looks like a blur, unless the subject keeps relatively still.
What are the Advantages of Analog Cameras?
- Analog video is a universal standard and has been for several decades. Virtually any analog CCTV camera can be plugged into any DVR, regardless of brand.
- CCTV literally is as simple as plugging a cable into the camera and into a DVR.
- Less expensive than IP Cameras
- Smaller amount of storage space required
Analogue signals can also be converted into a digital signal to enable the recordings to be stored on a PC as digital recordings. In that case the analogue video camera must be plugged directly into a video capture card in the computer, and the card then converts the analogue signal to digital. These cards are relatively cheap, but inevitably the resulting digital signals are compressed 5:1 (MPEG compression) in order for the video recordings to be saved on a continuous basis.
Another way to store recordings on a non-analogue media is through the use of a digital video recorder (DVR). Such a device is similar in functionality to a PC with a capture card and appropriate video recording software. Unlike PCs, most DVRs designed for CCTV purposes are embedded devices that require less maintenance and simpler setup than a PC-based solution, for a medium to large number of analogue cameras.
Some DVRs also allow digital broadcasting of the video signal, thus acting like a network camera. If a device does allow broadcasting of the video, but does not record it, then it’s called a video server. These devices effectively turn any analogue camera (or any analogue video signal) into a network TV.