Anti-copy protection for a video signal

Abstract

An apparatus and method for applying anti-copy protection to a raster-scanned video signal are described. A square waveform 52 is added to the vertical synchronisation pulses 50 of the video signal. The effect of the waveform is not apparent until it has been recorded by a video cassette recorder. The anti-copy protected video signal can therefore be viewed normally on a display device at or near to the picture quality intended by the originator of the video signal, but once recorded, exhibits a reduction in picture quality which makes the video signal quite unattractive to view.

1 . Apparatus for applying anti-copy-protection to a raster-scanned video signal to produce a modified video signal, the apparatus comprising: 
 an input for receiving a video signal which is to be modified, the video signal having vertical synchronisation pulses;    modifying means for modifying the vertical synchronisation pulses of a video signal received by the input to produce a modified video signal, the modified signal being viewable on a display device at or near to the quality intended by the originator of the video signal but such that after recording by a video cassette recorder, the average voltage level of a modified vertical synchronisation pulse is shifted towards the blanking level in comparison to the average level before recording, such that the recorded signal exhibits a reduction in vertical stability when played back and viewed on the display device; and    output means for outputting the modified video signal.    
   
   
       2 - 61 . (canceled)