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H I J
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Q R S
T U V
Variable bit rate.
Operation where the bit rate varies with time during the decoding of a
compressed bit stream.
Used in MPEG 1.
lens type that the focal length can be infinitely varied to give the
desired. It is similar to
a manual zoom lens, except that a varifocal lens cannot be zoom tracked.
See Video Distribution Amplifier.
An instrument similar to an oscilloscope, that is used to check and/or
amplitude and phase of the three
colour signals (RGB). It has a circular, rather than rectangular
screen, to show the phase angles
of the component colours.
Velocity of propagation.
Speed of signal transmission. In free space, electromagnetic waves
travel at the speed of light (C).
In coaxial cables, this speed is reduced by the
Commonly expressed as percentage
of the speed in free space i.e. 0.8C which is 0.8 x 3x108.
The portion of the video signal that occurs between the end of one
field and the
beginning of the next. During this time, the electron beams in the
turned off (invisible) so that
they can return from the bottom of the screen to the top
another scan. It is a time
period where information can be inserted such as teletext, K codes
Vertical interval switcher.
A sequential or matrix switcher that switches from one camera
exactly in the vertical interval, thus producing roll-free
switching. This is possible
only if the various camera sources
Chrominance and luminance detail expressed vertically in the picture
by the number of scan lines and the Kell factor (a probability
limit in a 625 line, 2:1 interlace
system is 409.5 lines. In a non or random interlace system
the resolution will be worse.
The return of the electron beam to the top of a television picture tube
or a camera pickup device target
at the completion of the field scan.
Vertical shift register.
The mechanism in CCD technology whereby charge is read out from
the photosensors of an interline
transfer or frame interline transfer sensor.
Vertical sync pulse (also field
sync pulse). A portion of the vertical blanking interval
made up of blanking
level lines of video. Synchronizes
vertical scan of television receiver to
signal. Starts each
frame at same vertical position. In total the vertical
interval is 20 line long (CCIR
Vestigial sideband transmission.
A system of transmission wherein the sideband on one side
carrier is transmitted only in part.
Video Graphics Array.
Video bandwidth. The
difference between the lowest and the highest signal frequency that a
specific video signal can reach.
The greater the video bandwidth, the better the quality of the
picture. A video
recorder that can reproduce
a very broad video bandwidth generates a very
detailed, high quality
picture on the
screen. The accepted bandwidth in CCTV is 5.5MHz for a
Video Distribution Amplifier
(VDA). A special
amplifier for buffering the video signal
it can be supplied to a number
of items of equipment at the same time. Each output
to be individually terminated at 75 Ohms.
Video gain. The amplification
factor through any piece of equipment. Many loopthrough
items are passive, i.e.. no gain.
Video equalization corrector
(video equalizer). A device that corrects for the high
losses and/or phase errors in the
transmission of a video signal along long lengths of cable.
A device that enables digital storage of one or more images for a
display on a video monitor.
Video in-line amplifier.
A device providing amplification of a video signal.
Video matrix switcher (VMS).
A device for switching more than one camera, VCR, video
printer and similar to more than
one monitor, VCR, video printer and similar.
complex and more powerful than
simple sequential video switchers.
Video monitor. A device
for converting a video signal into an image.
Video printer. A device
to produce a hard copy printout from a video signal. It may be
either a monochrome (B/W) or colour
printer. They come in different format sizes and
often special paper and inks are
needed. Many computers now can be fitted with a video
capture card, which means the print
can be produced using a normal computer printer.
Video signal. An electrical
signal containing all of the elements of the image produced by
or any other video source.
Video switcher. A
device for switching more than one camera to one or more monitors
manually, automatically or upon
receipt of an alarm condition.
Vertical Interval Test Signals. Specially shaped electronic
inserted in the
(in the case of PAL, usually between lines 6 & 18) that can be used
measurement of many quality factors
of a system.
Video wall. A video
wall is a large screen made up of several monitors placed close to one
another, so when viewed from a
distance, they form a single large video screen or
Video On Demand. A service that allows users to view whatever
they want it with VCR-like control capability such as pause,
VHF. Very High Frequency.
A signal encompassing frequencies between 30 and 300 MHz.
VHF band I uses frequencies between 45 MHz and 67 MHz,
180 MHz and 215 MHz for Band III.
Band II is reserved for FM radio from
88 MHz to
VHS. Video Home System.
As proposed by JVC, a video recording format used most
often in homes
but also in CCTV. Its limitations include the speed of
magnetic tapes used and the color
separation technique. Most of the CCTV equipment,
today, exceeds VHS resolution.
VLF. Very Low Frequency.
Refers to the frequencies in the band between 10 and 30 kHz.
VMD. Video Motion
Detector. A detection device generating an alarm condition in
to a change in the video signal,
usually motion, but it can also be change
in light. Very
difficult to set up for use externally but can be
in carefully controlled situations.
Modern VMD systems can learn the
scene and ignore such things as tree and foliage
Virtual Reality. Computer-generated images and audio that are
high-tech display and sensor systems
and whose imagery is under the control
of a viewer.
VS. Vertical Sync.