V

[This is preliminary documentation and subject to change.]

VBI

See vertical blanking interval.

vertical blanking interval

(VBI) The time period in which a television signal is not visible on the screen because of the vertical retrace (that is, the repositioning to top of screen to start a new scan). Data services can be transmitted using a portion of this signal. In a standard NTSC signal, perhaps 10 scan lines are potentially available per channel during the VBI. Each scan line represents a data transmission capacity of about 9600 baud.

VGA

See Video Graphics Array.

Video Access server

An out-of-process server that handles device contention among multiple instances of the ActiveX control for Microsoft WebTV for Windows. Device contention is conflict over which process controls a particular device.

Video control

An ActiveX control in Broadcast Architecture that applications use to control how the Video Access server presents audio and video streams. Unlike the Enhancement Video control, which also displays video, the Video control can be used in World Wide Web pages and stand-alone applications as well as in Microsoft WebTV for Windows. In contrast, the Enhancement Video control can be used only in Hypertext Markup Language (HTML) pages displayed by Microsoft® WebTV® for Windows®. However ,the Enhancement Video control automatically handles the connection between itself and WebTV for Windows, whereas the Video control does not. The Video control is provided with Broadcast Architecture.

Video Graphics Array

(VGA) A video standard created by IBM that supports several modes, including a graphics mode of 640 horizontal pixels by 480 vertical pixels with 2 or 16 simultaneous colors and a graphics mode of 320 horizontal pixels by 200 vertical pixels with 256 colors. The term VGA chip is often used generically to refer to a video controller chip.

VIF

See virtual interface.

virtual device driver

(VxD) A 32-bit, protected-mode driver that manages a system resource, such as a hardware device or installed software, so that more than one application can use the resource at the same time. VxD refers to a general virtual device driver — the x represents the type of device driver. For example, a virtual device driver for a display device is known as a VDD, a virtual device driver for a timer device is a VTD, a virtual device driver for a printer device is a VPD, and so on.

virtual interface

(VIF) A dynamic-link library that a Microsoft Multicast Router calls to package and transmit a stream in the format required by a particular broadcast output device. A virtual interface is valid only for the hardware and software configuration for which it was created, and thus each type of broadcast output device requires a different virtual interface.

VxD

See virtual device driver.