202 Digital CCTV
and seven days a week in time lapse mode, which allows a record-
ing of extended periods on video cassettes. High grade video
cassettes are needed to avoid damaging video recording heads.
Industrial grade tapes should be replaced after multiple uses.
DIGITAL VIDEO RECORDERS—DVRS
The biggest selling feature for digital surveillance to date has been
the switch from the video cassette recorder storage to digital
storage. The combination of affordable image compression tech-
nology and large capacity hard disks made the development of
digital video recorders feasible. Digital video storage or digital
video recorders (DVRs) are a practical replacement for analog
VCRs because of the elimination of problems such as poor image
quality from the reuse of tapes, worn out heads, scratches, and
stretching from searching back and forth for a specifi c scene. Wear
and tear aside, no matter how many guidelines are set up for the
management of conventional video tape, one of its biggest down-
falls is the simple action of having to place a tape into the VCR.
A digital video recorder is a stand-alone unit capable of
saving images to a hard disk. DVRs look similar to a standard VCR
in some ways, but that’s where the similarity ends. Because digital
systems are not mechanical like VCRs, factors such as frame speed
and video quality are software adjustable. Unlike the VCR, a
digital video recording device provides clear, sharp images every
time it is played. There are no tapes to store and material does not
deteriorate over time. A digital system allows for auditing of activ-
ity through monitor screen menus and for images to be retrieved
as easily as opening a fi le, using criteria such as date, time, loca-
tion, or camera number. Whatever role the DVR plays, its very
existence declares a system to be digital even though the camera,
transmission, and display technologies may be analog. Digital
video storage allows particular images to be retrieved as easily as
opening a fi le based on criteria such as date, time, location, camera
number, special index numbers, etc. Digital video storage
eliminates the need to store hundreds of space consuming VCR
tapes, and archived material does not deteriorate with time.

Get Digital CCTV now with O’Reilly online learning.

O’Reilly members experience live online training, plus books, videos, and digital content from 200+ publishers.