UFC 4-021-02NF
27 September 2006
change 1, 23 October 2006
4-14
FRAMES PER SECOND (FPS)
4-14.1
CCTV cameras transmit video in image frames. The measure of the
"smoothness" of the playback of the video is quantified in frames per second (fps).
Television video is displayed at 30 fps. For most security applications, 30 fps is higher
than needed for evidentiary and investigative purposes. Additionally, CCTV cameras
have the option to transmit video at two image rates: alarm condition and non-alarm
condition. Making use of a lower non-alarm fps can reduce project cost by allowing a
lower bandwidth transmission and storage requirement (recording) of the CCTV system.
4-14.2
Non-alarm frame speeds can fall in the 1 fps to 5 fps range (3 fps average).
4-14.3
Alarm condition frame speeds can fall in the 10 fps to 20 fps (15 fps average).
4-15
4-15.1
In general, the bandwidth required increases with the frame rate used. Use
this formula to calculate bandwidth:
Bandwidth = (pixels horizontal by vertical) * (frame rate in images/sec)
4-15.2
Sample calculations for a camera in nonalarm mode at 2 fps (Figure 4-12)
and in alarm mode at 10 fps (Figure 4-13) are provided to demonstrate the impact on
CCTV communication bandwidth requirements. The following assumptions apply for the
calculations:
4-15.2.1 Assumption #1: Resolution is 640 pixels by 480 pixels
4-15.2.2 Assumption #2: Compression ratio is 20:1
Figure 4-12. Calculation For a Camera in Nonalarm Mode at 2 FPS
At 2 bytes/pixel = 614,400 bytes, or 614.4 kb, per image.
Compression: 614.4kb per second (kpbs/20) = 30.7 kbps per image frame.
Camera rate is 2 frames/sec = 2 x 30.7 kbps = 61.4 kbps.
Convert bytes to bits (8bits/bytes + 2 control bits = 10 bits/byte)
Bandwidth = 61.4 kbps = 0.61 megabytes per second (Mbps).
Thus one camera in normal (nonalarm) monitoring transmits video at a bandwidth of
0.61 Mbps.
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