Method and apparatus for television signal scrambling using vertical sync replacement
AssigneeGeneral Instrument Corporation
InventorsTimothy D. Rea, Alfred W. Stufflet, Kevin T. Chang
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Abstract
A method and device for scrambling video signals for broadcast in a proprietary television system includes modifying the vertical or horizontal synchronization pulses of the video signal to prevent unauthorized viewers from properly displaying the programming content. Preferably, the vertical sync pulses are removed from the signal prior to broadcast and replaced with horizontal sync pulses. A descrambler used with the receiving television uses the manner in which the false horizontal sync pulses were inserted into the video signal to recreate a sufficient approximation of the vertical sync pulses.
Claims15
A method of controlling access to a broadcast video signal by scrambling said video signal, said method comprising modifying a horizontal sync component of said video signal.
A method of controlling access to a broadcast video signal by scrambling said video signal, said method comprising:
- removing a vertical sync component from said video signal;
- and
- inserting a horizontal sync signal in said video signal in place of said removed vertical sync component to produce a modified video signal, said inserted signal excluding any data regarding said scrambling.
A scrambler for scrambling a video signal comprising:
- an input terminal for receiving a video signal;
- a signal conditioner which receives said video signal from said input terminal and removes therefrom a vertical sync component of said video signal
- a sync processor which receives said video signal from said input terminal and synchronizes with said video signal to generate a horizontal sync component;
- and
- a multiplexer which receives an output signal from said signal conditioner and said horizontal sync component from said sync processor;
- wherein said multiplexer inserts said horizontal sync component in said video signal in place of said extracted vertical sync component;
- and
- wherein said scrambler does not insert data regarding said scrambling in that portion of said video signal from which said vertical sync component was removed.
A descrambler for unscrambling a scrambled video signal which has been scrambled by inserting a horizontal sync signal component in place of a vertical sync signal component, said descrambler comprising:
- an input terminal for receiving said scrambled video signal;
- a scramble mode data receiver for extracting scramble mode data from said scrambled video signal;
- a control logic circuit;
- a vertical sync generator controlled by said control logic circuit for generating a vertical sync component based on said extracted scramble mode data output by said scramble mode data receiver;
- and
- a multiplexer, controlled by said control logic circuit, for receiving said scrambled video signal from said input terminal, receiving said vertical sync component from said vertical sync generator, and inserting said vertical sync component into said scrambled video signal so as to produce an unscrambled video signal.
A method of descrambling a video signal that has been scrambled by a process including inserting a horizontal sync signal component in place of a vertical sync signal component and inserting scramble mode data at a portion of said video signal other than where said vertical sync signal was replaced, said method comprising:
- extracting said scramble mode data;
- generating a vertical sync signal based on said extracted scramble mode data;
- and
- inserting said generated vertical sync signal in said video signal so as to produce an unscrambled video signal.
Dependencies are inferred from the claim text.