Patent ID: 8498519

Claim:
An apparatus for modifying a video signal comprising: an input for receiving an analog video signal of the type having horizontal synchronisation pulses and in which colour information is transmitted on a subcarrier signal, the video signal having a colour burst comprising a subcarrier signal at a reference frequency which is used to generate a reference subcarrier signal in the receiver for demodulating the colour information, and wherein the phase of the colour subcarrier in the video signal, when compared with the horizontal synchronisation pulse, is substantially different on every line, the apparatus comprising; a signal generator arranged to add a protection signal to the video signal in the vicinity of the colour burst, such that upon recording of the video signal by a video cassette recorder the protection signal interferes with the operation of the video cassette recorder causing errors in the colour burst recorded, wherein the signal generator is arranged to add 6 cycles of protection signal to the video signal, the amplitudes of the first two cycles being different to those of the last four cycles, wherein the signal generator is arranged to generate the protection signals having a peak to peak amplitude of oscillation in the range 10 mV to 750 mV, wherein the signal generator is arranged to add five pulses between a line synchronisation pulse and the colour burst of the input video signal, and wherein the signal generator is arranged to generate pulses of decreasing amplitude; an output for outputting a modified video signal comprising the video signal and the protection signal, wherein when the modified video signal has been recorded by a video recorder, playback of the modified video signal exhibits visual artefacts that are not visible before recording of the modified signal occurred, and wherein the signal generator is configured to add the protection signal to the video signal such that the protection signal is phase-locked to the horizontal synchronisation pulse and such that the protection signal has a frequency that is substantially similar to the colour subcarrier, and wherein the signal generator is configured to add the protection signal such that it interferes with the colour killer circuits of a video cassette recorder.