SEM Security Systems
a division of Southeast Mobility
Digital Video Recorder
The digital video recorder or DVR
(also referred to as a NVR or network video recorder when connected to the camera
with cat5) is the heart of your CCTV system. Not long ago
all video was recorded onto VHS tapes and you would find a stack of them head
high right next to the recorder. VHS tapes were better than nothing but had a
couple of draw backs. First you had to continually swap tapes when the one in the
recorder neared it's end. Of course they had to be labeled and kept in such an
order that when the new tape was about full, you could find the oldest tape to
replace it with. Then there was the issue of retrieving video recordings. You had to
search through the tapes, assuming that you labeled them properly as you
swapped them out, and find the day of interest. Next you had to fast forward
through the tape until you found the time of the day that you were looking for. All of
these issues and a lot of others have been solved with today's DVR.
DVR's typically come in a 4, 8, 16, and 32 port configuration. This indicates the
maximum number of cameras that can be attached to the DVR. If you look at your
needs and decide that you have to have 5 cameras, then you will have to install an
8 port DVR. Of course this leaves you 3 empty ports that you can add cameras to
later if needed.
A DVR is nothing more than a computer. It may have a different shape, stand up
right, or lay flat on a shelf but if it walks like a duck and quacks like a duck, it's a
duck or a computer in this case. All video is stored to a computer hard drive. Now
when you get ready to find video that happened last week you just use an on screen or computer
key board to enter the date and time you are interested in and it is retrieved
instantly for you to view. What happens when the hard drive gets full? The
computer will start recording over the oldest video on file. Once the system is
installed and you see that you are only getting 3 weeks of recording history and
you really wanted 6, you simply add in another hard drive.
DVR's offer other advantages. Remote viewing for instance. With all but the
cheapest DVR's you will have ethernet capability which allows you to view video
from anywhere on your local network using your lap top or even your smart phone,
or anywhere in the world via the internet and your broad band connection.
One question that I'm always asked is "how long will it keep a history of
recordings?". That depends on a lot of factors. First there is the number of
cameras that are attached to the DVR, more cameras equals less recording time.
Then there is the recording video quality, higher quality recorded video equals less
recording time. Next is the recording speed. Some of the cheaper DVR's will
display 30 frames per second to the screen when you are viewing real time but
may record at a maximum of 2 frames per second. Higher recorded frame rates
equals less recording time. Obviously the size of the hard drive to which the video
is stored is going to be a factor. Another factor is whether the cameras are
recording full time. With all but the cheesiest of DVR's you can designate each
camera to record full time or when motion is detected. This is a function within the
DVR, not a motion detector added to the system. When the DVR detects movement
in the received video, it will start recording and stop recording when the motion
stops. Another capability that our equipment offers, and one that we typically use
is that we can record continously at 1 or 2 frames a second, then when motion is
detected it will start recording at a higher frame rate that provides full motion
when you rewatch it. You can also usually set the cameras up on a schedule. For instance we
want camera number 1 to record 24/7 but camera 2 we want to record full time
during work hours, say from 8 to 5, and then record on motion at night and on
weekends. These options where unheard of in the days of video tape.
Some DVR's will have a DVD burner built in so that you can save a particular video
to DVD to be used later in court for instance. Some have "hot swappable" hard
drives so that you can easily slip out a hard drive that is about full and slide a new
one back in it's place.
One thing that may not be so obvious is the user interface or UI. We have worked
with some DVR's that were so intuitive that you really didn't need a manual to
operate them. It was as easy as pointing with the mouse and clicking and the DVR
did exactly what you expected it to do. However, we have worked with others
where it was absolutely mandatory that you read the users manual and then call
the manufacturers technical support line and have them explain it to you again. By
the time you decide you need to do something else with the DVR you have
forgotten how to do it and you're back in the manual again trying to figure it out.
Definitely take the time to look at the UI, you will glad you did 6 months down the
road when you need to go back and make a recording of that incident that just
Again you get what you pay for and the capabilities of the DVR need to be
matched to your budget and the video quality that you expect from the cameras.