Variable bitrate
Operation in which the bitrate varies with time during the decoding of a compressed bitstream. Although a variable bit rate is acceptable for plain linear playback, one reason not to use a variable bit rate is that reasonably quick random access becomes nearly impossible. Additionally, because MPEG has no table of contents or index, the only tool the play-back system has for approximating the correct byte position is the requested play-back time stamp and the bit rate of the MPEG stream. Approximating this time stamp is nontrivial because MPEG streams do not encode their play-back time.

VLC (Variable Length Coding)
A reversible procedure for coding that assigns shorter code words to frequent events and longer code words to less frequent events.

Vertical blanking interval (VBI)
Lines 1-21 of the video top field and lines 263-284 of the bottom field, in which frame numbers, picture stops, chapter stops, white flags, closed captions, etc. may be encoded. These lines do not appear on the display screen, but maintain image stability and enhance image access.

Vertical interval time code (VITC)
SMPTE time code inserted in the vertical blanking interval between the two fields of a tape frame. This method eliminates errors that occur from tape stretch when using longitudinal time code.

VHS (Video Home System)
Popular consumer videotape format developed by Matsushita and JVC.

Vibrant Color Quality (VCQ)
Uses 32-bit color accuracy throughout the rendering pipeline. All internal calculations are executed with 32-bit accuracy and the end result is dithered down to the original color depth from a true color palette.

Video
A system of recording and transmitting primarily visual information by translating moving or still images into electrical signals. The term video properly refers only to the picture -- but as a generic term, video usually embraces audio and other signals that are part of a complete program. Video now includes not only broadcast television, but many non-broadcast applications, such as corporate communications, marketing, home entertainment, games, teletext, security, and even the visual display units of computer-based technology.

Video black
The absence of pictures and sound during video playback, usually at the beginning and ends of a program, and between segments; "dead" video.

Video-on-CD or Video CD
A full-motion digital video format using MPEG video compression and incorporating a variety of VCR-like control capabilities. See also White Book.

Video 8 or 8mm Video
Video format based on the 8 mm videotapes popularized by camcorders.

Video sequence
A series of one or more pictures.

Videotape formats
In general, classified by the width of the magnetic tape used:

1" -- Used for professional or "broadcast quality" video recording and editing; comes in large, open reels.

3/4" -- U-matic (Sony). Most industrial video uses this format, stored in inch-thick cassettes.

1/2" -- Cassette-based, primarily consumer format. VHS -- the most popular home videotape format -- is 1/2", as is SonyÕs Beta format. Their higher-quality counterparts (Super-VHS and Super Beta, respectively) are also in the 1/2" format.

8mm -- New consumer format that provides high-quality recording in tiny tape format; popularly used in hand-held camera-recorders (camcorders). See Video 8.

Vsync
The period of time when the screen is paused for a few microseconds and is getting ready to draw the next frame.

VRAM
Short for video RAM, and pronounced vee-ram. VRAM is special-purpose memory used by video adapters. Unlike conventional RAM, VRAM can be accessed by two different devices simultaneously. This enables the RAMDAC to access the VRAM for screen updates at the same time that the video processor provides new data. VRAM yields better graphics performance but is more expensive than normal RAM. A special type of VRAM, called Windows RAM (WRAM), yields even better performance than conventional VRAM.