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Macrovision of Sunnyvale, California, already sells a widely used system to
prevent people pirating DVD recordings by simply connecting a recorder to the
DVD output. Now the company has developed a system that stops people recording
from the standard VGA monitor output of a computer by feeding it through a
commercial VGA-to-video converter (WO 99/977). The VGA signal contains the
colour information together with vertical and horizontal synchronisation pulses.
Macrovision advances the horizontal pulses slightly. The picture looks fine on
the monitor, but the converter cannot use the signal.