Importance

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Abstract

A DES decrypting unit decrypts video data frames encrypted and compressed based on MPEG standards, when receiving them. The decrypted video data frames are expanded one by one in a MPEG expansion circuit. Each time the single frame is expanded, the MPEG expansion circuit outputs a completion-of-frame-expansion signal to a host control CPU. The host control CPU counts the completion-of-frame-expansion signals and reduces an accounting count value in an accounting data memory in accordance with this count value. The host control CPU output character pattern image data from a pattern generator when the accounting count value becomes 0. The character pattern image data is superimposed on a video signal in an adder circuit.

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First Claim