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Time Lapse, VCR's, DVR's, NVR's ...
With a DVR machine set to record continuously; in the previous example any recordings made 7 - 10 days before would automatically have been scrubbed off, or to be accurate "over written", unless the machine were fitted with a larger internal HDD (or external 'RAID' array); or there was a mechanism in place for archiving all of the recordings onto the hard disc.
Although larger capacity disc drives are becoming more widely available (as they reduce in cost), the option of archiving all the data rarely if ever happens, the simple reason being that data is mostly written to an HDD much faster than is possible to other forms of 'affordable' removable media. Ideally, the use of a DVR with removable HDD packs would provide the ideal solution, so as one disc becomes full, it can then be removed, locked away and replaced with a new unit.
Generally speaking if there is an incident, the system operator will locate the relevant section of recording and copy it to removable media such as CD-R, DV cassette, DAT, compact Flash, or recordable DVD.
If budgets permit, particularly where a number of recorders are being used, Doktor Jon would always recommend looking at a quality DVR that offers removable hard drives, simply to provide the four key requirements:- 1) Maximum resolution, 2) Good images per second rate 3) a minimum 30 days recordings available, and 4) little risk of the Police having to seize the machine complete with its recorded evidence.
There is an increasing trend in some countries (at present, relatively little in the UK), to build Digital Video Recorders into PC computer cases. Whilst this does provide a very affordable option for certain situations, it is unlikely to take off here in a very big way, simply due to the prohibitive costs involved in complying with all relevant EU Directives, and also the variable quality of components used by different manufacturers. Some may be very good, but others can be an absolute disaster.
Now the biggest benefit in using any HDD based recorder is the seamless access to any event anywhere on the disc; with a tape based system (analogue or Digital), you generally have to wind through miles of tape to get to the bit you want, although if youre looking for a suspect or incident, you often have to go through it all anyway. With a DVR, you simply skip across the disc directly to the time or portion that youre looking for.
In a Forensic Surveillance situation where an unknown suspect is being sought anywhere on the recording, there really is no significant advantage for digital over analogue. That said, there are certain situations where a high end DVR fitted with advanced 'semi intelligent' search facilities, can speed up the whole recording analysis process.
In practice, Digital HDD recorders are simply brilliant for real time applications, such as hospitals or shopping centres (Malls), where a lost child or a suspect can be searched for quickly and efficiently, with loads of pictures at maximum resolution.
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