METHOD OF AND APPARATUS FOR TRANSMITTING DATA

摘要

A transmitted video data bit stream contains complete data frames(I frames) and differentially coded data frames (P and B frames). I frames are sent less frequently than P and B frames because they contain more data. However, I frames are required in order to allow late entry and to allow recovery from transmission errors. Encryption synchronisation frames are also transmitted. Periodically, for the same reasons and may be included in the data bit stream by addition to or stealing from the bit stream. Encryption synchronisation frames (9) are sent immediately prior to I frames (8). This ensures that, no matter where a user begins receipt of the data bit stream (20), both encryption synchronisation information in the form of an encryption synchronisation frame (9) and an I frame (8) will be received in quick succession and decoding will commence with a minimum delay.