Standard NVR uses hard disk drives (HDD) for storage
of video footage. HDD with a form factor of 3.5” and a SATA interface
has a large storage capacity such as 2 Terabytes (TB) or more as of
November 2012 and is inexpensive. Micro SD card is small in physical
size and rigid storage capacity. We have 32GB as the largest capacity
at present. Fortunately, we can allocate the whole lot of 32GB to one
camera whereas the HDD storage of 2TB will be shared by 10 or whatever
count of cameras supported by the NVR.
Micro SD card is not designed for high volume or high speed recording.
It is used for camera edge storage mainly for its small size and low
cost. As such, we have to reduce our expectation of the quality of the
recording from edge storage. For a 4 mega-pixel camera equipped with
H264 compression, we should be able to achieve 2 frames per second on
edge whereas it would be 12 frames per second with central storage.
Video footage is meant for review. In order to review the footage
recorded at the edge, we will need to connect the camera to a PC or
server via a standard IP network cable unless the camera has been
equipped with wireless transmission. This is the requirement at least
for setting up the camera initially before deployment. The footage
files will be in a standard format for snapshots and could be in a
proprietary format for video clips. We will supply a software program
to play back the video clips in a PC running Windows. Files would have
been set up to have date and time as part of the filename for ease of
reference. See Slide 2. It is not possible to obtain live views of
the camera without connecting the camera to an IP network full time.
While edge camera is easy to install and low cost, it does not enjoy the
benefits offered by a centralised NVR. Even if edge is connected with
IP full time, we can review the footage on a file basis only and not in
synchronization with other cameras with a graphical user interface as
offered by NVR. There are indeed situations where centralised storage
is too expensive to achieve and edge is an acceptable compromise.
We can also use edge as a back up of centralised storage. If we store
snapshots only in edge, we will have footage for a long period such as
one or two months. These snapshots could be valuable in case the NVR
does not support such a long recording period or when the NVR breaks
down when it is needed for police investigation.
As of November 2012, the Compucon stable has 4 models with edge
storage. They are K3911, K5211E, K7111 and K7311. See Slide 3.