sat behind a multiplexer, this made multiplexing several cameras onto a single
video cassette tape possible (Fig. 7.2).
DVRs were first introduced in traditional analog systems. DVRs can digi-
tize video inputs from analog video surveillance cameras and also have the
functionality of a multiplexer. Hard disks are the recording media for DVRs,
thus eliminating the need to consistently change out or store tapes.
DVRs evolved further to include an Ethernet network connection, thus allow-
ing the digital video to be transmitted over a data network and opening up the
possibility of viewing video remotely through a web browser. Digital recording
brought new functionality to video surveillance such as the capability to detect
motion in a picture, to record at different frame rates based on the detection of
motion, view video while recording video and more.
The next digital evolution of video recording occurred when the DVR was
replaced with a video server, that is, a data network server with video manage-
ment software. In this arrangement analog or digital cameras connect to the
server and the server connects to the network. The video server uses standard
data network equipment and becomes the centerpiece of a video surveillance
system. Because the server is on a network it opens up a wide variety of func-
tions for recording, storing, viewing, and administering the system, either on
the network or off site (Fig. 7.3).
A major advantage of the video server is that the functionality of the system
is derived from software rather than hardware as was the case with older
analog video surveillance systems. For example, an administrator or an author-
ized user can determine and set the number of inputs, the resolution required
and so forth for viewing multiple cameras or video on a monitor or screen.
Analog
CameraCoaxial Cable
Local Area
NetworkPersonal Computer
with Browser or
Client SoftwareCameraAnalog DVRAnalog
CameraNetwork
SwitchFigure 7.2 Video surveillance—networked (DVR)
Video Surveillance Systems 87