Patent ID: 8542980

Claim:
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 a blanking section with a first set of equalization pulses followed by vertical synchronization pulses followed by a second set of equalization pulses; circuitry configured to modify the vertical synchronization pulses of the 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 synchronization 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 an output configured to output the modified video signal.