Specifications

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KNOW-HOW: Compression Methods
KNOW-HOW · KNOW-HOW · KNOW-HOW · KNOW-HOW · KNOW-HOW · KNOW-HOW · KNOW-HOW
S15
Comparing the two sequences, one can now quite easily see how the
amount of data is reduced. The more static, i.e. the more unchanged
the picture is, the smaller the amount of data is which has to be
recorded, or vice versa: the larger the changes, the smaller is the ad-
vantage of the storage space of MPEG-4.
Is is very hard to predict the recording time in a simple table.
A part of a table for the DVR-1640A is shown to illustrate this.
Let’s assume, 10 cameras are connected to this recorder and each of
them records 5 pictures/sec. This results in a recording speed of
50 pictures/sec.
static: recorded picture sequences without great changes to the
pictures by high-quality cameras of low noise
complex: frequent change of pictures/a lot of movement/little noise
The table shows different recording times which depend on the qual-
ity and condition of the picture.
At continuous recording, 96 hours of static pictures and 58 hours of
complex pictures can be recorded.
What kind of conditions may additionally affect the recording time?
The application of motion detection and timers do not enhance the ac-
tual recording time, but the time available is distributed more useful.
Thus, it is possible, e.g. when using a timer setting of 10 hours a day
and activating the motion detection, the recording time can be distrib-
uted to 10 or more days.
The affect on the quality of the camera pictures is more crucial. At
twilight or if a spider’s web is moving in front of the camera, for ex-
ample, a camera signal which is not of low-noise is recognised by the
units as a sequence with full change of the picture contents. Especially
due to the noise, the luminosity of almost every pixel changes. In such
cases, the recording time may be reduced to a quarter or below.
Thus, it is always recommendable to use high-quality cameras with re-
spective lenses and to ensure sufficient illumination.
Conclusion:
The recording times of sequences recorded by MPEG-4 method can-
not be predicted for certain.
The times of the units stated in the tables are approximate values only.
The storage requirement can be five times as much if the picture qual-
ity is poor and thus reducing the recording time considerably.
Recording capacity in hours for the DVR-1640A
Recording in PAL mode at a hard disk capacity of 640GB
Resolution of the system: 720 x 576
Picture quality / Picture condition / Picture size in KB
LOW STANDARD HIGHEST
static complex static complex static complex
8.42KB 13.70KB 11.86KB 19.56KB 18.60KB 30.05 KB
100 212 128 148 90 96 58
96 218 134 154 96 102 64
64 332 204 236 140 148 90
50 422 262 300 180 192 116
32 660 404 468 282 300 186
16 1318 812 934 570 596 372
Recording speed
pictures/sec.)
DVR-1640A, see page S 6