A method of operation of an audio/video content receiver having a content decoder capable of decoding an audio/video program from a packetized data stream by using data packets defining decryption information comprises the steps of: receiving encoded audio/video content as a packetized data stream comprising one or more programs having data packets identified by respective sets of one or more packet identifiers and comprising identification data mapping programs to respective sets of the packet identifiers; selecting data packets from the packetized data stream for a required program according to the set of packet identifiers defined by the identification data for that stream in respect of the required program; selecting further data packets from the packetized data stream from which a program is selected which have packet identifiers not included in the identification data for that packetized data stream; generating a composite packetized data stream from the selected packets; generating composite stream identification data indicating packet identifiers of packets included in the composite packetized data stream; and supplying the composite packetized data stream to the content decoder for decoding the program from the composite packetized data stream according to the packet identifiers in the composite stream identification data.