How long will a digital video recorder (DVR) record for? Sixty days of recording is required but the product that has been purchased only offers 30 days – What can one do next? Here are a few key facts that one should take into account when purchasing a DVR.
Frame rates
There is plenty of hype in the marketplace about what each product brand in digital storage is capable of.
In South Africa, with a very few exceptions, the frequency of the National Power Grid means that the cameras used must be PAL. Therefore, the maximum field rate is 50 fields per second and frame rate is 25 frames per second, ie one frame = two fields. There are claims made by some of 60 fields and 30 frames. However, these relate to NTSC, which is a different frequency.
Video capture cards come in a wide variety of configurations. Some have a single input, others have four inputs, some six and some eight. The key to the frame rate is the processor used on the card and whether or not a processor is applied to any one input or all four, six or eight. This is due to the fact that individual processors will theoretically each give one the required 25 frames per second, real time viewing. In addition, the rest of the hardware and a quality software package is required to continue the frame rate through to viewing and storage systems.
Data transfer rates and key issues
Hardware
In hardware specifications one hears talk of processors, varying hard drives, bus speeds, etc. But what does it all mean? In simple terms, one's aim is to deliver information from a CCTV camera to a screen and/or storage system as quickly and as accurately as possible. However, an incorrect set-up with conflicting hardware can create problems. Furthermore, unstable software could lead to added problems with system falling over and missing crucial information. Therefore, it is advisable to talk to people are knowledgeable in the field of digital video recording, rather than settling for cheaper options, as in many instances taking the cheaper route will mean that one will have to pay for a replacement system later.
Software
Approximately 95% of software platforms run on Microsoft Windows in South Africa. Therefore the majority of digital recorders sold in this country are either Windows-based or run on MS-DOS with a linking module. Within those that are Windows-based there are those that run on Windows 98 and Millennium(ME), and those that run on Windows NT4 and/or Windows 2000 Professional/2000 Server. It is important to realise that Win 98 and ME must run Defragmentation of discs at least once a month otherwise in the majority of cases they will fall-over - a 75 GB hard-drive can take up to 4 h to 'defrag' and all programmes must be closed; so no recording or monitoring during this time.
File size
People are now becoming more familiar with digital compression jargon - bitmap, giff, tiff, Mpeg, Jpeg, Moving-Jpeg, Wavelet, etc. These all reduce a set picture size to a smaller picture size by various means and at various percentages of the original. Some look for movement change from one frame to the next and apply a maximum 20% update remembering the 80% from the previous image. Others take the old picture and using different algorithms create a new picture at a greatly reduced frame size. At present, most digital recorders in the marketplace use Mpeg, Jpeg, M-Jpeg or Wavelet.
In considering any digital system, the frame size combined with the frame rate determines a specific data rate per second. If the hardware or software that has been selected cannot cope, then the system will not run effectively. Furthermore, if the data speed of backup does not allow for one's per-second capacity, as in some DAT tape backup systems, one could lose information or need to compensate by reducing frame rate. It is therefore advisable to select a system with alternative back-up options and perhaps a system with full redundancy.
Conclusion
There is a wide range of digital recorders on the market. Any well-produced digital recorder should support all digital storage systems. Remember that hardware and software play a big part in keeping a system stable, but more importantly the frame size and frame rate play the most important part in fulfilling one's requirements as a security and management solution. Furthermore, never be afraid to find out what the competitive products are and what their strengths and weaknesses are. One should also ensure that the system installed has expansion potential to fully integrate more cameras, additional back-up and service one's growth.
For details contact Niall Beazley, Vision Catcher on tel: (011) 465 6396 or [email protected]
Final checkpoints for the purchasing of the right digital video recorder
1. Frame rates and file size
2. Compression
3. Hardware
4. Operating system, software and future upgrades
5. Data back-up
6. Data rates for transfer, back-up and supporting programmes
7. Number of cameras supported
8. System expansion potential
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