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FAQ |
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| Q |
How can we determine the capacity of a
storage and how long it can store data? |
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A
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The main factors in defining the storage
capable period are number of cameras(A), frames per
second
(FPS, B), image size per frame(KByte/frame, C) and audio input or
not. Mostly user set
the number of frames per second they want
in DVR system. (30 FPS supports full motion picture)
Basically, image size per frame is determined a resolution(640 x
480, 320*240, etc ) and motion
sensitivity of objects.
Although,
motion sensitivity related with video compression, the rate is hard to
evaluate. The size of one frame is
about 4~5KB on the average according to tested data. Based
on
the factors above, the
storage capable period can be calculated with the formula below;
Storage capable period = storage capacity of DVR / (A x B x C)
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| Q |
Is DVR system extendible? |
| A |
Yes it is. Either add or detach internal HDD or
external storages to the system.
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| Q |
What
video compression method usually used in a DVR
system? |
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A
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Usually, MPEG4, MPEG2, M-JPEG, H.263, Wavelet used
in the DVR system. Anyway, every
compression method has
its advantages and disadvantages. It is flexible to choose
compression
method under system environment or user
's
specific need.
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| Q |
What's the easiest way to differentiate functions as
well as features of
the various DVR systems? |
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A
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Apparently, perform check on the system specification. Then, compare
how many camera inputs
and total display channels the system
supports. It is also important to know whether the
system is
capable of real-time video display and
simultaneous recording video data of each channel. Lastly,
check
wehther the system supports a variety of network
environment.
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| Q |
What's the basic principles of a
multiplexer and a time Lapse VCR? |
| A |
Multiplexer and a time lapse VCR are
essential and required in
analog CCTV system. Multiplexer
transforms parallel
video signals into serial signs from channels.
After that, it
inputs them to a
time lapse VCR. It also reorganize signals
to display recorded video data. Assume there are 4
channel camera inputs connected to a
multiplexer.
Assume again the system records 30 frames per second totally.
It
will be 7.5 frames per second
per channel. In order,
it records
data from camera A1, A2, A3 and A5 and repeat the
same process
over again. Distinctive mark is stamped on the
magnetic tape of a frame identifies each frame, in
order to be reorganized again. Example, it has to
reorganize frames from camera A1 only through a
multiplexer again to produce the whole video
data from the camera A1.
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| Q |
Is extra devices needed to access
the system in a remote area? If yes, is it completely secured?
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A
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No need of
extra devices for a remote access if network available. Due to
security reasons,
however, user have to install the software provided by
the manufacturer and authorized ID
and password.
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| Q |
Is there a big price difference between
CCTV system and DVR system? |
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A
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Initially,
the cost of DVR system used to be very
expensive than CCTV system when DVR system is
introduced to
the market in late '90's. Anyway, with rapid development of technology and
popularization, DVR system
has gained competitiveness in two aspects. Those are price and
quality. Nowadays, DVR system is cheaper than CCTV system in terms of
initial cost and
maintenance fee.
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| Q |
Is it possible for me to monitor the
system when on a business trip abroad?
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| A |
Yes it is. DVR supports remote monitoring and
browse
through various network including PSTN
as well as LAN.
Besides that, it also
makes remote data transmission possible and even
zoom/pan/tilt control of each and every
camera.
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| Q |
Why is video/audio compression technology
important in
developing DVR system? |
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A
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Apparently,
the size image is calculated by 'actual image sizex8/8'. In other
words, 640x480 sized
image is about 300KB and will be 540KB to display as
a video data for one minute. (calculated by
300KBx30framesx60 seconds = 540MB) Therefore 1 GB of Hard
disk can store 2-minute video
data
if it is not compressed. Anyway, high compression
rate does not always mean the best way.
It is
extremely important to maintain high picture quality while
data is compressed and that is
the technology all
about.
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| Q |
Do we
need a multiplexer or a time lapse VCR or a quad when we
set up DVR system ?
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A
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No, of
course. DVR provides functions which
a multiplexer or a quad is supposed to do.
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| Q |
What factors do we need to concern to choose an
appropriate DVR system? |
| A |
1. There shouldn't
have bug or an error
in the system. |
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2. It is
important to have an automatic recovery system when error detected. |
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3. A
protection circuits for a video data processing board is needed |
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4. Recording and
the display speed is
assumed as the core functionality in the DVR
system.
In other words, video data processing chip
that corresponds to camera channels as well as
supporting high data compression rate
needed. |
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5. It
gives the best picture quality. It is
highly recommendable if the system can support
optimum
event, monitoring and analysis without
critical image distortion or fragment. Video or image data
can be used
as evidence. It will be very helpful if comparison
to
different
products.
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| Q |
What's
the advantages of Stand alone DVR if compared with PC-based
DVR? |
| A |
1.
Stand alone DVR, embedded OS(operating
system), is extremely stable system solving
problems
that happened in a desktop with its unstable OS. |
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2.
Stand alone DVR is compact
in size that all-in-one
system integrates all functions to one board.
It
is also easy to produce in large amount and
therefore reduce the system
cost. |
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