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| HOW A MULTIPLEXER WORKS Multiplxers are now classed as old technology and is surpassed by the market leading Avermedia Range of DVRs. MAS are Main Distributors for the market leading AverMedia Range of DVRs which incorporate the latest hybrid technology - they can record analogue, IP cameras and other remote DVR's.
A video multiplexer is a digital device used for manipulating the images from CCTV cameras. Its primary function allows the recording of a number of cameras onto a single VCR. There are three main functions of a video multiplexer: · Encoding – taking a single picture from each camera in turn and feeding it out to a VCR in rapid succession. A ‘Simplex’ video multiplexer is capable of performing any one of the above functions at any one time, a ‘Duplex’ machine is capable of performing two functions simultaneously including encoding of cameras and generating a live multiscreen picture of the camera images. With a Duplex machine it is possible to encode all the cameras whilst decoding a previously recorded tape. This does, however, require the use of two VCRs. Video multiplexers are available in a variety of models to suit various applications. Including ‘Simplex’ or ‘Duplex’, monochrome or colour with 4 to 16 camera inputs. Most units come equipped with digital activity or motion detection, automatically taking more pictures from cameras where changes in the video signal have been detected. ‘Triplex’ units allow simultaneous recording and playback of cameras and multiscreen display with both live and play back images. Allowing an operator to continue monitoring the site whilst reviewing previously recorded images. The more cameras that are encoded to a single VCR, the greater the delay between updated images from any one camera. The theoretical maximum rate a multiplexer can encode camera pictures, is 50 fields per second. If a multiplexer is encoding 16 cameras, the minimum gap between successive picture updates from any one camera is 16/50 second, approximately 1/3 second. When a video multiplexer is combined with a time-lapse VCR the delays between updates further increase. In 24-hour mode a VCR will record one image in eight presented to it. The minimum gap between successive picture updates increases to (8x16)/50 seconds, approximately 2.5 seconds. This does not appear to be a long time but it is clear that a considerable proportion of the available information from any camera is not recorded and the probability of obtaining optimum recorded images of an incident are considerably reduced. In order to reduce the delays between picture updates it is recommended that a maximum of 8 cameras are recorded onto a single VCR. This is a standard that is followed in the majority of town centre surveillance systems. |
| FAQs How do I transfer information from a DVR to a tape? As long as your DVR features a composite monitor output for playback then all you need to do is loop the video through the VCR, for example Monitor Output to VCR IN, VCR OUT to Monitor IN. Whatever you view on the system you can now record on the VCR. If you're using a domestic VCR you may require a scart to BNC cable. The most common cause of this problem is the synchronisation between the multiplexer and VCR. To generate fields at the same rate ensure the recording times are the same on both units, for example 24hours on the multiplexer and 24hours on the VCR. If this does not work then either a sync cable or vext cable will be required. Multiplexers are designed with sync or swipe pulse inputs. Many VCRs produce a synchronising pulse at a connector at the back of the recorder. The pulse generated by the VCR controls the rate at which the multiplexer switches between cameras. Connecting this pulse to an input of the multiplexer enables the multiplexer to send fields to the VCR at exactly the right rate for the time lapse setting selected. |
