发明公开
EP0187483A3 Improved video encryption system 失效
改进的视频加密系统

Improved video encryption system
摘要:
@ An encrypted video distribution system includes a signal originating station which distributes television signals in a format unrecoverable by a standard television receiver. In particular, the normally occurring vertical and horizonal synchronizing pulses are deleted and, optionally also, video information is selectively inverted about a voltage reference potential intermediate the black and white levels. To permit synchronization restoration, a keying pulse is transmitted once each video field, and a synchronizing digital code burst transmitted once each frame - all at a fixed, predetermined intra-frame timed relationship. At each authorized subscriber location, the keying pulse and digital code burst are employed to lock a receiver frame clock which derivatively gives rise to all requisite reception- permitting synchronizing pulses. The transmitted information also contains information sufficient to restore the inverted video program content.
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