Videotape anti-copying encryption scheme

Abstract

Anti-copying protection for video material is provided wherein at least one high-amplitude pulse is inserted into various lines of the video signal, in and immediately preceding the vertical interval associated with each field, during the process of preparing a master recording for use in the high-speed duplication of legitimate recordings of the video material. A preferred embodiment of the present system and method is directed to videotape-to-videotape anti-copying protection. A high-amplitude pulse is inserted in the back porch region of horizontal sync pulses, and immediately following certain equalizing and vertical sync pulses, at an intermediate stage in the mastering process, whereby the pulse is inserted into a separated luminance component of the video signal, which is later recombined with the chromenance signal. Such method allows for the insertion of an higher amplitude pulse than would otherwise be possible, and yields a pulse of the desired final width, without the occurrence of such undesirable effects as loss of color lock or darkening of the picture with respect to legitimate recordings. The resulting modified video material may be viewed properly on a TV receiver or other display, but when coping from the legitimate source is attempted, the copy will yield a video signal which is too distorted for proper viewing. A further modification of the value of negative-going horizontal sync pulses provides additional synchronization error in recorded copies of legitimately recorded video material so as to further render such materials effectively non-copiable.