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VA

Volt-ampere, it measures apparent power in a reactive circuit found by multiplying the voltage by the current.

Variable Focus Lens
Lens of which the focal length can be continuously varied between set limits.  The lens must be refocused with each change in focal length.

VHF

It is the abbreviation for Very High Frequency, designated by ITU for the 30 to 300 MHz band of frequencies.

VHS

It is the abbreviation for Video Home System.

Video

It is pertaining to picture information in a television system.  These pictures information are basically a three-dimensional array of color pixels.  Two dimensions serve as spatial (horizontal and vertical) directions of the moving pictures, and one dimension represents the time domain.  A data frame is a set of all pixels that correspond to a single time moment. Basically, a frame is the same as a still picture.

Video Codec

A video codec is a device or software that enables video compression and/or decompression for digital video.  A variety of codecs can be implemented with relative ease on PCs and in consumer electronics equipment.  It is therefore possible for multiple codecs to be available in the same product, avoiding the need to choose a single dominant codec for compatibility reasons.  In the end it seems unlikely that one codec will replace them all. Starting with a chronological-order list of the ones specified in international standards, some widely-used video codecs are H.261,MPEG-1 Part 2, MPEG-2 Part2, H.263, MPEG-4 Part 2, MPEG-4 Part 10 or H.264,etc.

Video Compression

Video Compression refers to reducing the quantity of data used to represent digital video images, and is a combination of spatial image compression and temporal motion compensation.  Most video compression is lossy — it operates on the premise that much of the data present before compression is not necessary for achieving good perceptual quality.  For example, DVDs use a video coding standard called MPEG-2 that can compress around two hours of video data by 15 to 30 times, while still producing a picture quality that is generally considered high-quality for standard-definition video.  Video compression is a tradeoff between disk space, video quality, and the cost of hardware required to decompress the video in a reasonable time.  However, if the video is over compressed in a lossy manner, visible (and sometimes distracting) artifacts can appear.

Video compression typically operates on square-shaped groups of neighboring pixels, often called macroblocks.  These pixel groups or blocks of pixels are compared from one frame to the next and the video compression codec (encode/decode scheme) sends only the differences within those blocks.  This works extremely well if the video has no motion. A still frame of text, for example, can be repeated with very little transmitted data.  In areas of video with more motion, more pixels change from one frame to the next. When more pixels change, the video compression scheme must send more data to keep up with the larger number of pixels that are changing. If the video content includes an explosion, flames, a flock of thousands of birds, or any other image with a great deal of high-frequency detail, the quality will decrease, or the variable bit rate must be increased to render this added information with the same level of detail.

Video Drive

With a video driven lens, the video signal is picked up from the AI connector, which is connected to the camera.  Because the lens adjusts the iris based on the video signal, the lens is referred to as a video drive lens.

Video Encoder or Video Server

A video encoder, or video server, makes it possible to move toward a network video system without having to discard existing analog equipment.  It is ideal for integration with existing analog CCTV (closed circuit television) system.  A video encoder brings new functionality to analog equipment and eliminates the need for dedicated equipment such as coaxial cabling, monitors and DVRs – the latter becoming unnecessary as video recording can be done using standard PC servers.

A video encoder typically has between one and four analog ports for analog cameras to plug into, as well as an Ethernet port for connection to the network. Like network cameras, it contains a built-in Web server, a compression chip and an operating system so that incoming analog feeds can be converted into digital video, transmitted and recorded over the computer network for easier accessibility and viewing.  Besides the video input, a video encoder also includes other functionalities and information which are transported over the same network connection: digital inputs and outputs (I/O, which can be used to trigger the server to start recording and transmitting images, or activate alarms and devices such as lights and doors), audio, serial port(s) for serial data or control of pan/tilt/zoom cameras and devices.  With image buffers, it can send pre-alarm images.  A video encoder can also be connected to a wide variety of specialized cameras, such as a highly sensitive black and white camera, a miniature or a microscope camera.

Vignette

This is the phenomenon when illumination on the screen progressively diminishes from the center to the corners.  There are two kinds of vignette: natural vignette caused by the lens, and vignette that caused by improper use of accessories such as a lens hood or filter.

Virtual Private Network, VPN

This creates a secure “tunnel” between the points within the VPN. Only devices with the correct "key" will be able to work within the VPN. The VPN network can be within a company LAN (Local Area Network), but different sites can also be connected over the Internet in a secure way.  One common use for VPN is for connecting a remote computer to the corporate network, via e.g. a direct phone line or via the Internet.

VLF

It is the abbreviation for Very Low Frequency, designated by ITU for the 3 to 30 kHz band of frequencies.

Volt

It is the unit of electromotive force.

Voltage

It is electrical potential of electromotive force expressed in volts.

Voltage Drop

It happens when the voltage developed across a component or conductor by the current flow through the resistance or impedance of the component or conductor.

Voltage Rating

It refers to the highest voltage that may be continuously applied to a cable construction in conformance with standards or specifications.