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Viewers often complain that the soundtrack of a television programme is out
of sync with the picture, says the BBC. This “lipsync” problem is often caused
by digital editing: sounds and pictures are handled separately, and small timing
errors tend to creep in. These errors add up and soon become noticeable. So the
BBC has devised a system that keeps track of the errors and throws away tiny,
scarcely noticeable slices of the picture or soundtrack as soon as the mistiming
becomes a problem (WO 98/54909).