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V
 Variable bit rate.  Operation where the bit rate varies with time during the decoding of a
compressed bit stream.  Used in MPEG 1.
Varifocal.  A lens type that the focal length can be infinitely varied to give the exact image
desired.  It is similar to a manual zoom lens, except that a varifocal lens cannot be zoom tracked.
VDA.  See Video Distribution Amplifier.
Vectorscope.  An instrument similar to an oscilloscope, that is used to check and/or align
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 dielectric material.
Commonly expressed as percentage of the speed in free space i.e. 0.8C which is 0.8 x 3x10⁸.
Vertical interval.  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 monitors are
turned off (invisible) so that they can return from the bottom of the screen to the top to begin
another scan.  It is a time period where information can be inserted such as teletext, K codes
and telemetry.
Vertical interval switcher.  A sequential or matrix switcher that switches from one camera
to another exactly in the vertical interval, thus producing roll-free switching.  This is possible
only if the various camera sources are synchronized.
Vertical resolution.  Chrominance and luminance detail expressed vertically in the picture
tube. Limited by the number of scan lines and the Kell factor (a probability factor).  The
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.
Vertical retrace.  The return of the electron beam to the top of a television picture tube screen
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 which is
made up of blanking level lines of video.  Synchronizes vertical scan of television receiver to
composite video signal.  Starts each frame at same vertical position.  In total the vertical
interval is 20 line long (CCIR & PAL).
Vestigial sideband transmission.  A system of transmission wherein the sideband on one side
of the carrier is transmitted only in part.
VGA.  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
colour signal.
Video Distribution Amplifier (VDA).  A special amplifier for buffering the video signal so that
it can be supplied to a number of items of equipment at the same time.  Each output will need
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 frequency
losses and/or phase errors in the transmission of a video signal along long lengths of cable.
Video framestore.  A device that enables digital storage of one or more images for a "frozen"
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.  Much more
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
a camera 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.
VITS.  Vertical Interval Test Signals.  Specially shaped electronic signals inserted in the
invisible lines (in the case of PAL, usually between lines 6 & 18) that can be used for the
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 wall.
VOD.  Video On Demand.  A service that allows users to view whatever program they
want whenever they want it with VCR-like control capability such as pause, fast forward
and rewind.
VHF.  Very High Frequency.  A signal encompassing frequencies between 30 and 300 MHz.
 In television, VHF band I uses frequencies between 45 MHz and 67 MHz, and between
180 MHz and 215 MHz for Band III.  Band II is reserved for FM radio from 88 MHz to
108 MHz.
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 recording, the
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 response
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 useful in carefully controlled situations.
Modern VMD systems can learn the scene and ignore such things as tree and foliage
movement.
VR.  Virtual Reality.  Computer-generated images and audio that are experienced through
high-tech display and sensor systems  and whose imagery is under the control of a viewer.
VS.  Vertical Sync.
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