A method of selecting data for multiple carriage partial encryption consistent with certain embodiments involves examining unencrypted packets of data in a digital audio/video data stream to identify a packet type; and selecting packets of the identified packet type for multiple partial encryption, wherein...http://www.google.com.hk/patents/US7319753?utm_source=gb-gplus-share專利 US7319753 - Partial encryption and PID mapping
