Digital Video Multiplex Recorders (DVMRs) are the security products of the moment – and understandably so. Across many key CCTV performance factors such as picture quality, image storage, event searching and verification, Digital CCTV technology has the potential to offer convenience and quality far beyond that which analogue technology is capable of providing.
For the installer, installation is easy … less kit means less to physically install. For the security manager the use of cutting edge technology both improves efficiency and reduces cost.
DVMRs are being promoted as the latest and greatest security product. Yet by attempting to provide the newest features, many fail to offer some of the more fundamental security benefits.
The net result of a good digital product should be a decrease in the overall capital cost of a system, with no VCR, tapes or maintenance being required. However many DVMRs don’t allow users to play and record at the same time. Therefore to the unwary customer, often the actual requirement is for two large and very expensive systems, not just two VCRs and a standard multiplexer. Another important ,and often overlooked, consideration is system control; the management of telemetry and larger systems from single or multiple control points. Ask: Can the product can be integrated? And look for a digital product which is an ‘all in one box’ solution.
Picture Compression
M-JPEG has become something of an industry standard amongst security manufacturers. Most of the other compression methods have been developed for different industries such as broadcasting or camcorder usage. As with most applications, different customers require different capabilities. Therefore ensure that the DVMR you invest in is well established and will offer longevity. Typically, systems using either MPEG, JPEG, Wavelet or H:261 are suitable for most security applications. A key consideration regarding compression format focuses upon whether or not you need to network your DVMR. Wavelet compression, although designed for security usage, is not a format which is commonly supported on corporate IT networks and is therefore somewhat restrictive.
Typical analogue systems record at 6 pictures per second (PPS) in 24 hour mode. Most digital recording products have a maximum recording speed of between 25 and 50 PPS. In theory, this allows single or multiple channels to record at near live speed. Connecting more cameras to a product will share the record speed, so that 25PPS becomes 12.5 per camera across two inputs and so on. Important to note is that the speed at which the record rate is set will determine how quickly the storage capability is filled. For example, a good quality picture at 25KB, recording at 25 PPS will use approximately 56GB of space in 24 hours.
More expensive DVMR’s can achieve 50 PPS, even per channel, but remember that larger images mean your storage space fills more quickly. Pick a system to suit needs and budget.
For many years DVMRs have relied on digital tape technology and so have not delivered the true benefits of digital. With tape based systems, just like traditional VCR systems, the mechanical devices soon wear out, so requiring human intervention, maintenance and further expenditure. With the decreasing cost of hard disk drives, leading DVMRs can now offer cost effective, instant access RAID storage devices for more than 3000GB – truly hands-free, maintenance free systems.
The less an image is compressed, the higher its quality will be. Unfortunately, however, the less you compress an image, the more information needs to be stored and hence the file size is larger. A balance is therefore required, which makes it imperative that your choice of digital system provides flexibility when setting the image size.
Most manufacturers offer a choice of quality between 0 and 75KB, but it is important to note that the overall quality isn’t always related to size – it also depends upon the DVMR processor. As an example, an image recorded on one DVMR, may be worse than a 30KB image on another.
Referring to my earlier point about technology being appropriate for security use, the same is true of hardware and software. A PC based Windows system, which we all know are prone to ‘crash’ every now and again (and usually unpredictably), would obviously not be suitable as the foundation of a high-level security system. Users should also question the abilities of their security guards when working with PCs and their work environments.
As most of us will be aware, there are currently many 1st and 2nd generation DVR products.
There are many choices open to your customer. It is for these reasons that I mention ease-of-use as the last, but most important point to consider. As with any successful new technology, users don’t (and shouldn’t) need to understand how it works in order to use it.
The key to unlocking the effectiveness of digital video technology is a simple and intuitive user interface.
