Menetelmä digitaalisessa muodossa siirrettävän televisiolähetyksen salaamiseksi

摘要

The invention relates to a method for scrambling a digitally transmitted television signal which may comprise several different programs and is transmitted in a transmission channel in the form of digital video data packets and the accompanying sound is transmitted in the same transmission channel in the form of digital audio data packets and possible other data are transmitted in data packets. All packets are transmitted as a combined signal in one transmission channel and it is essential that some of the data packets related to a particular program are scrambled and some are transmitted without scrambling. Then a signal received without descrambling can be seen and heard but with a poor quality of image and sound. A good image and sound quality can be obtained only by attaching a descrambling device to the receiver. In the various embodiments of the invention, the video signal packets to be scrambled are selected on the image area as the function of time or place or both or in a seemingly random fashion. In the various embodiments of the invention, the audio signal packets to be scrambled are selected periodically or in a seemingly random fashion. The scrambling depth can be varied by varying the proportion of the packets transmitted scrambled. The scrambling is done separately for the audio and video signals related to different programs transmitted on the same transmission channel.