vertical blanking interval

The part of a TV signal that is sent between each video frame. In North American TV (NTSC), the vertical blanking interval (VBI) takes up the last 45 lines of each 525-line frame. Its purpose is to allow the TV time to reposition its electron beam from the bottom of the current frame (screen) to the top of the next one. This non-viewable part of the signal is used to transmit closed-caption content. See datacasting, V-chip and ATV Forum.

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