An improved method and apparatus for providing a copy-protected video signal

摘要

A anti-copy programme signal is provided. Copies of the anti-copy video pulses made on a video recorder experience reduced quality and interference in playback making them unpleasant to watch. The uncopied signal can be viewed without any material effect on picture quality. The signal comprises a pulse 28 added to each line 6 of the signal throughout both the visible picture region and throughout the vertical blanking region 12, as well as a first modulated wave-form 34 added to the vertical synchronisation pulses 16 of the signal and a second modulated wave-form 36 added to several lines 6 of the picture signal before the vertical blanking section 12. The presence of all three of these features together has been found to be provide a surprising accumulative effectiveness in causing interference in the reproduction of the modified video signal during playback of the copied video signal, that is greater than the effectiveness provided by the different features taken separately.