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Definition: vertical blanking interval

The part of an analog TV signal that was sent between each video frame. In the North American TV (NTSC) signal, the vertical blanking interval (VBI) was the last 45 lines of each 525-line frame. Its purpose was to allow the CRT 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 was also used to transmit closed-caption content. See digital blanking interval, datacasting, V-chip, ATV Forum and vertical sync.