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VERTICAL BLANKING INTERVAL (VBI)



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VERTICAL BLANKING INTERVAL (VBI) - Part of the TV signal that is not used for video information and left available to transmit other data such as captions, Web data, current stock market prices. Visually the VBI is the black stripe at the top and bottom of a TV picture and physically it constitutes 21 lines' worth of the total 525 lines transmitted per second in the NTSC TV signal. In detail, the Vertical Blanking Interval is a portion of the analog TV signal embedded inside two rectangular fields on the TV screen that are comprised of 262.5 imperceptible horizontal lines. Each line is made of 427 pixels that form the video images on the screen through a process called electron beam called "interlaced scanning". The first 21 lines of each of the two horizontal fields (a black stripe - only seen when the picture loses its vertical hold and rolls) is called the Vertical Blanking Interval. In this interval, data of any kind can be broadcasted, received by any TV set, and interpreted with special software if the TV set is hooked into a set-top box or the data is received by a TV tuner card on a computer. The first 9 lines of the VBI are used for timing information of the shows, but lines 10-20 are pretty much unused. Line 21, however, is used for closed captioning text and now in use for HTML data. See HTML.

VIDEO SERVER - The business end of a client/server setup, a server is usually a computer that provides the information, files, Web pages, and other services to the client that logs on to it. (The word server is also used to describe the software and operating system designed to run server hardware.)
VIDEO-ON-DEMAND (VOD) - The service of providing content through subscriber selection off a

large menu of options, available to viewer at any time.





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