Copy protection for video signal using narrowed horizontal synchronization signals
View Patent ↗Enhancements to a video anticopying process that causes an abnormally low amplitude video signal to be recorded on an illegal copy. The enhancements in one version introduce into the overscan portion of the television picture, just prior to the horizontal or vertical sync signals but in active video, a negative going waveform that appears to the television receiver or videotape recorder to be a sync signal, thereby causing an early horizontal or vertical retrace. One version provides (in the right overscan portion of the picture), a checker pattern of alternating gray and black areas which causes the TV set on which the illegal copy is played to horizontally retrace earlier than normal in selected lines with a consequential horizontal shift of the picture information on those lines. This substantially degrades picture viewability. In another version a gray pattern at the bottom overscan portion of the picture causes vertical picture instability. In another version selected horizontal sync signals are narrowed, causing irregular vertical retraces. Also provided is apparatus for removing or attenuating these enhancements from the video signal, to allow copying.
1. Apparatus for narrowing line synchronization pulses in a video signal which includes positive going pulses to cause a reduced amplitude video signal on a recorded copy by a video recorder, comprising:
a first timing circuit to provide indications of synchronizing pulses of the video signal:
a line selector circuit to provide a line selector signal indicative of at least one set of selected lines of the video signal, wherein one or more of the selected lines is at a location in a non-overscan area;
a second timing circuit to provide the narrow line synchronization pulses each being in a horizontal blanking interval of the video signal; and
logic circuitry to combine the line selector signal with the output of the second timing circuit and which provides a video signal including the positive going pulses and the narrow line synchronization pulses and which provides a normal color picture when played on a conventional TV set, the narrow line synchronization pulses each being prior to a color burst in at least one of the horizontal blanking intervals, wherein the narrow line synchronization pulses enhance a copy protection effect provided by the positive going pulses thereby to inhibit recording.
2. The apparatus of claim 1 , wherein at least one of the positive going pulses is provided following a pseudo sync pulse.
3. The apparatus of claim 1 , wherein the positive going pulses are each AGC pulses.
4. The apparatus of claim 1 , wherein the positive going pulses are AGC pulses which are provided in at least one blanking interval of the video signal.
5. The apparatus of claim 1 , wherein the narrow line synchronization pulses occur after vertical sync pulses or at the end of field lines of the video signal.
6. The apparatus of claim 5 , wherein the narrow line synchronization pulses cause sensing of early or late vertical pulses on a TV set when playing a copy of the video signal.
7. Apparatus for providing narrow line synchronization pulses, comprising:
an input terminal for receiving a video signal;
a first portion coupled to the input terminal to provide the narrow line synchronization pulses in horizontal blanking intervals of the video signal;
a second portion coupled to provide a basic copy protection signal; and
an output terminal coupled to the first and second portions and which provides a copy protected video signal with the basic copy protection signal and with the narrow line synchronization pulses prior to a color burst in the horizontal blanking interval and which provides a normal color picture when played on a conventional TV set, wherein the basic copy protection signal causes a reduced amplitude of a recording of the output copy protected video signal, whereby a copy protection effect of the basic copy protection signal is enhanced thereby to inhibit recording.
8. The apparatus of claim 7 , wherein the basic copy protection signal includes at least one AGC pulse or at least one pseudo sync pulse.
9. The apparatus of claim 1 , wherein only the selected lines include the narrow line synchronization pulses.
10. The apparatus of claim 7 , wherein only selected scan lines of the video signal include the narrow line synchronization pulses.