FAQ
 
1.   How can we determine the capacity of a storage and how long it can store data?
2.   Is DVR system storage extendible?
3.   What video compression method usually used in a DVR system?
4.   What's the easiest way to differentiate  functions as well as features of the various DVR
      systems?
5.   What's the basic principles of a multiplexer and a time Lapse VCR?
6.   Is extra devices needed to access the system in a remote area? If yes, is it completely secured?
7.   Is it a very big price difference between CCTV system and DVR system?
8.   Is it possible for me to monitor the system when on a business trip abroad?
9.   Why is  video/audio compression technology important  in developing DVR system?
10. Do we need a multiplexer or a time lapse VCR or a quad when we set up DVR system ?
11. What factors do we need to concern to choose an appropriate DVR system?
12. What's the advantages of Stand alone DVR if compared with PC-based DVR?
 
 
Q How can we determine the capacity of a storage and how long it can store data?

A

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?

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?

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? 

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?

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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Is it possible for me to monitor the system when on a business trip abroad?
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?

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 ?

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.
  2. It is important to have an automatic recovery system when error detected.
  3. A protection circuits for a video data processing board is needed
  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.
  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.
  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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