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DIGITAL VIDEO
RECORDERS (DVRs)
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The DVR (digital video recorder) has replaced
the VCR as the device used to record CCTV
video for detection and documentation
purposes.
The DVR can be networked for viewing images
over the internet, however a distinction has
been established in the industry between a
DVR and an NVR (networkable video recorder).
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DVRs accept analog signals via coax cable
connected with BNC terminations.
Some DVRs can be networked and can be
accessed remotely over the internet, not all
DVRs have this capability.
RJ-45 PORT FOR
CONNECTIVITY TO
THE INTERNET
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An NVR is strictly a digital device that only
accepts digital signals via RJ-45 connections
and is specifically designed for remote viewing
over the internet.
Cameras are managed through a PoE switch
and then networked into the NVR which is
considerably different than a DVR.
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NVR: 4/8/16 CHANNEL
NOTICE THAT THERE ARE NO
CAMERA PORTS ON THIS
DEVICE, CAMERAS ARE
CONNECTED TO A NETWORK
SWITCH
DVR: 8 CHANNEL WITH
NETWORK CONNECTION
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Whether it’s a DVR, hybrid DVR or NVR they all
have the same basic features and functions and
they all have the option to record audio.
These devices are menu driven and a
considerable amount of time can be spent in
configuring a DVR
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A DVR CCTV system provides a multitude of
advanced functions over VCR technology including
video searches by event, time, date and camera.
There is also much more control over quality and
frame rate allowing disk space usage to be optimized
and the DVR can also be set to overwrite the oldest
security footage should the disk become full.
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CCTV SYSTEMS
One of the main considerations in choosing a DVR is
it’s storage capacity.
DVR’S come in 250GB, 500GB, 1TB and 2TB
storage capacities just to name a few.
The numbers are associated with the hard drives in a
DVR, many DVRs are customizable upon request.
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Hard drives can also be swapped out, if a hard drive
crashes it can be easily replaced with a new SATA
(serial advanced technology attachment) drive.
A smaller hard drive can be replaced with a larger
drive as needed.
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This diagram shows the inside of a DVR.
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There is another type of hard drive to mention
though SATA is the most popular.
PATA (parallel ATA) drives are an older standard
and were prevalent up to 2007.
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Other factors that will have implications on the
storage capacity of the DVR:
Frames per second 30fps or less
Resolutions- high res. vs low res.
Continual recording vs motion only recording
Audio recording
Compression standards
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In the DVR menu for recording set up it will ask
you to pick a value for frames per second, you
will be able to choose 1 to 30fps.
1 to 20fps is a fairly choppy video image while
30fps is a smooth video image, the lower the
fps the choppier the video.
Using the 30fps selection uses more disk
space.
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The DVR menu under video setup will ask you
to pick a resolution.
Under VGA (video graphics array) you will be
able to choose 1024 x 768 or 1280 x 1024,
some DVRs may give you more choices.
The higher the resolution is the more disk space
that will be used.
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In the DVR menu for camera setup you will be
given an option to motion record which means
that when the camera senses motion it will start
recording.
The other option would be continuous recording
which again will use more disk space.
It should be noted that motion sensing by a
camera is done at a fairly close range, so
continuous recording can pick up an event by
several cameras for better angles.
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The compression standard is built into the DVR
and is not configurable by the operator.
There are many video compression standards
in use today, the most popular for DVRs are:
MPEG-2 or MPEG-4
JPEG-2000
H.263 and H.264 a UTI-T standard
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The latest compression standard is the H.264
The H.264 video format has a very broad
range that covers all forms of digital
video from low bit-rate Internet streaming
applications to HDTV broadcast and digital
applications with nearly lossless coding.
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With the use of H.264, bit rate savings of 50% or
more are reported.
For example, H.264 has been reported to give the
same Digital Satellite TV quality as current MPEG-2
implementations with less than half the bitrate, with
current MPEG-2 implementations working at around
3.5 Mbit/s and H.264 at only 1.5 Mbit/s.
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To date the H.264/MPEG 4 compression
standard provides the best image details with
the best compression rate to save disk space.
Most of the older (2 years ago) DVRs have
H.263 or MPEG-2 compression standards,
these standards are not that old and are still
used today.
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Some DVRs are quoted with a quadplex
function which means it can record, playback,
backup and perform network transfer all at the
same time.
DVRs can also provide e-mail notification of an
alarm event.
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DVRs are password protected, you can choose
not to use a password or if a password code is
configured and later forgotten the DVR has to
be re-set internally.
There is no reset button like those seen on
wireless routers, the DVR’s housing has to be
removed and an internal electronic jumper has
to be shorted.
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The exact jumper to short is determined by the
manufacturer, that information can be obtained
by the supplier.
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Some of the other recording functions of most DVRs
are the recycle function, it overwrites the oldest data
and keeps recording and saving the newest video for
about a week or so.
Triplex function (record, playback and remote
access, all can be done at the same time).
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Lets look at some of the connections on the back
of a DVR.
We will look at each connections more closely.
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The USB port is for an external mouse to navigate
menu options rather than using he controls on the
front of the DVR.
The other USB is for
A flash drive.
The CH1 through CH8 BNC ports are the camera
inputs, some DVRs have two BNC ports per channel
which allows for any camera to be viewed on a
different monitor.
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The main out VGA is for
an LCD monitor, the BNC
main out is for a CRT
monitor.
The RJ-45 port (LAN) is
for networking the DVR.
VGA MAIN
OUT
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The green termination block is for alarm inputs such as PIR
(passive infra-red) motion detectors or door switches. 1 thru 4
are for the positive lead and the “G” is a common ground for
each alarm device.
The alarm out provides 3 connections: N.O. (normally open)
COM (common) and a “G” for ground, this can be used for a
sounder or other notification device.
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The RS485 connection is for a PTZ controller
(A and B) with a ground connection which is
usually used for the shield connection.
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The audio connection on this DVR is similar to a VGA
connection and requires a special audio cable.
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Here is the a
DVR with all
of the
connections
made to the
interfaces we
just looked at.
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Here are the controls on the front of a DVR,
these are pretty common from manufacturer to
manufacturer.
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A closer look at the controls, again this is a
typical layout for most DVRs.
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A very important aspect of DVR interfaces is
being able to retrieve recorded video footage
and transfer it to another media device.
This is done through the use of a DVD/RW drive
which is available in some DVRs.
Increasingly though most DVRs provide USB
ports to transfer video onto a memory stick.
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This DVR has a USB port on the front for
downloading video onto a memory stick (jump
drive or USB flash drive).
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To view recorded video that’s been retrieved
from a DVR a special MPEG CODEC needs to
be downloaded to decode the video images.
These can be obtained from the supplier or
downloaded for free from the internet.
Sometimes the CODEC will be downloaded
onto your stick the first time you retrieve video
from the DVR.
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This DVR also has a scrolling knob, another
common feature found on 16 channel systems
which allows the operator to easily fast forward or
reverse through video footage quickly.
TOGGLE CONTROL
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This diagram shows the interconnections for
networking a DVR.
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Here is a micro DVR that is about the size of flash
drive for those of you that have everything….
Micro DVR with built In camera supports up-to 2Gb
micro SD card to record up to 2 hours of video.