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Variable bit rate. Operation where the bit rate
varies with time during the decoding of a compressed bit stream.
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 color signals (RGB). Velocity of propagation. Speed of signal transmission. In free space, electromagnetic waves travel at the speed of light. In coaxial cables, this speed is reduced by the dielectric material. Commonly expressed as percentage of the speed in free space. 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. 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. 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. A portion of the vertical blanking interval which is made up of blanking level. Synchronizes vertical scan of television receiver to composite video signal. Starts each frame at same vertical position. 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 highest signal frequency that a specific video signal can reach. The higher the video bandwidth, the better the quality of the picture. A video recorder that can produce a very broad video bandwidth generates a very detailed, high quality picture on the screen. Video bandwidths used in studio work vary between 3 and 12 MHz. Video distribution amplifier (VDA). A special amplifier for strengthening the video signal so that it can be supplied to a number of video monitors at the same time. Video gain. The range of light-to-dark values of the image that are proportional to the voltage difference between the black and white voltage levels of the video signal. Expressed on the waveform monitor by the voltage level of the whitest whites in the active picture signal. Video gain is related to the contrast of the video image. Video equalization corrector (video equalizer). A device that corrects for unequal frequency losses and/or phase errors in the transmission of a video signal. Video framestore. A device that enables digital storage of one or more images for steady 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 video switchers. Video monitor. A device for converting a video signal into an image. Video printer. A device for converting a video signal to a hard copy printout. It could be a monochrome (B/W) or color. They come in different format sizes. Special paper is needed. Video signal. An electrical signal containing all of the elements of the image produced by a camera or any other source of video information. 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. Video insertion test signals. Specially shaped electronic signals inserted in the invisible lines (in the case of PAL, lines 17, 18, 330 and 331) that determine the quality of reception. 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 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 supersedes 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 practical in CCTV as the VMD analyzes exactly what the camera sees, i.e., there are no blind spots. 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. WAN. Wide area network. Waveform monitor. Oscilloscope used to display the video waveform. Wavelet. A particular type of video compression that is especially suitable for CCTV. Offers higher compression ratio with equal or better quality to JPEG. White balance. An electronic process used in video cameras to retain true colors. It is performed electronically on the basis of a white object in the picture. White level. This part of the video signal electronically represents the white part of an image. It resides at 0.7 V from the blanking level, whereas the black part is taken as 0 V. Wow and flutter. Wow refers to low frequency variations in pitch while flutter refers to high-frequency variations in pitch caused by variations in the tape-to-head speed of a tape machine. W-VHS. A new wide-VHS standard proposed by JVC, featuring a high resolution format and an aspect ratio of 16:9. Y/C. A video format found in Super-VHS video recorders. Luminance is marked with Y and is produced separate to the C, which stands for chrominance. Thus, an S-VHS output Y/C requires two coaxial cables for a perfect output. Y, R-Y, B-Y. The general set of component video signals used in the PAL system as well as for some encoder and most decoder applications in NTSC systems; Y is the luminance signal, R-Y is the first color difference signal and B-Y is the second color difference signal. Y, U, V. Luminance and color difference components for PAL systems; Y, B-Y, R-Y with new names; the derivation from RGB is identical. Z. In electronics and television this is usually a code for impedance. Zoom lens. A camera lens that can vary the focal length while keeping the object in focus, giving an impression of coming closer to or going away from an object. It is usually controlled by a keyboard with buttons that are marked zoom-in and zoom-out. Zoom ratio. A mathematical expression of the two extremes of focal length available on a particular zoom lens. |