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VCR to DVR to NVR & IP Based Security
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The VCR
First came the camera and monitor, closely followed by the Video Cassette Recorder (VCR), recording one video stream to a 3-hour tape at 25 frames per second and often triggered by an input device (raid button in a bank, for example).
Technology then brought us the multiplexer, which allowed several streams of video to be recorded onto the same tape and separated out into discrete, viewable streams on replay and the time-lapse VCR which enabled the dropping of frames and in so doing permitted a 3-hour tape to be used over much longer periods, albeit at the cost of lost information.
The DVR
The rapid development of video compression algorithms (JPEG, MJPEG, MPEG-4, etc.), computer processing speeds and a rapid reduction in data storage costs then gave rise to the DVR. This you could consider as being the functionality of a multiplexer together with a computer disk for storage in place of tape, all housed in the same box together with some additional ports for connectivity.
The DVR provides a convenient, if limited, replacement for the multiplexer + VCR combination and provides non-linear access to recorded material usually selected by camera ID, time and date. The consistency of quality of recorded material will in general be higher than that obtained with analog tape although the actual quality achieved may or may not be better, depending on the compression algorithm and individual configuration.
In general more programmable options for individual video stream recording parameters, (picture resolution, number of frames per second, trigger options, start/stop times etc), are available, but a DVR is only useful where the analog cameras are all cabled back to the DVR’s location. Competent DVRs now feature UDP (CAT 5) network ports so that the device can be provided with an IP address and thereby become accessible over an Ethernet network.
The NVR
The Network Video Recorder heralds the arrival of the next natural point in the development of recording technology.
It is important to differentiate between DVRs and NVRs, as both are often termed ‘digital’. A DVR digitally compresses analog video feeds and stores them on a hard-drive, the term ‘digital’ referring to the compression and storage technology, not the transmitted video images. The DVR therefore has to be located near the analog feeds. In contrast an NVR stores digital images directly from the IP network.
Therefore the most obvious difference between the DVR and NVR is that whereas the DVR records from analog streams provided from analog cameras the NVR records video streams that have already been encoded at the cameras. Thus you find no video connectors anywhere on a NVR; it’s input and output is IP data comprising compressed and encoded video. This will typically be in MPEG-4 format which has enjoyed widespread adoption in the CCTV industry as the current compression technology of choice, due largely to its efficiency.
The huge advantage of architecture based on NVRs is that they can be located anywhere on a network – at the monitoring center, adjacent to camera clusters, on the edge of a network, collected together in a hardened environment, indeed anywhere at all. In use their location is transparent to an operator – he or she simply calls up the recorded video stream to be viewed and, provided that they have the necessary authorization there it is. NVRs record and replay simultaneously, and recordings on any one machine can be remotely viewed by a number of authorised operators spread across the network simultaneously, all totally independently and without affecting each other.
The importance of the independence of physical location, well away from the cameras if necessary, should not be underestimated – IT Managers are notoriously zealous in safeguarding their network capacity and rightly so, but by calculating the data flow requirement across the network and strategically placing NVRs accordingly, the impact of video streaming on bandwidth usage can be minimised. Typically an NVR might be placed on a Local Area Network (LAN) and near (in network terms, not necessarily physically) a camera cluster so that the load is carried by the local LAN capable of absorbing it easily, thus saving capacity on other, perhaps more restricted, parts of the network. The IT Manager can specify what level of bandwidth he is prepared to make available for video streaming and this can be set as a cap, so that it is not exceeded under worst-case conditions when in operation.
Then, when a recording is required at any other point on the network (typically “at center”, but not necessarily so) it can be called up seamlessly by the operator, streamed down and then analyzed, viewed (not the same thing) and acted upon accordingly.
“Mirroring” techniques are now often used to duplicate the recording of video streams on additional NVRs located at different parts of the network, which provides a high level of protection against network failure; if one part goes down the other is there as a backup. You can have as many NVRs across a system as you like – adding another is just a matter of plugging it in and configuring it. There is no requirement for additional video cabling. This feature really comes into its own during the consolidation of several independent systems into one managed environment, or in system rationalization or expansion as it reduces system complexity and removes all of the cost associated with re-cabling.
For more information regarding the further advantages of IP solutions, see our section on IP technology here: Link to IP page.
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