A method of scrambling a television signal and a method of and apparatus for descrambling a television signal is provided. An audio signal is used on which a key signal containing compression information and information concerning the position of a vertical blanking interval is superimposed on a portion...http://www.google.com.hk/patents/US5113441?utm_source=gb-gplus-share專利 US5113441 - Method for scrambling a television signal and method and apparatus for descrambling a scrambled television signal
