A video signal processor is capable of executing on/off control of a copy inhibiting process and rendering extremely difficult any illegal cancellation of the copy inhibiting process by a third person. This video signal processor includes an obstructor for obstructing proper recording of a video signal;...http://www.google.com.hk/patents/US5668873?utm_source=gb-gplus-share專利 US5668873 - Video signal processor with copy prevention function
