Multiplexing programs into a single transport stream without PID conflicts

In order to avoid Packet Identifier (PID) conflicts in multiplexed MPEG-2 program streams, the PID's are re-mapped, in real-time, with unique values, by use of look-up tables. In operation, each program stream transport packet contains a PID value and each program stream has an associated stream identifier (eg queue ID, QID). The PID 11 is used to index a first table 10 for generating an offset value 13. The offset value is then used to address a region 22 of a second table which contains a plurality of new PID values capable of being mapped to the original PID value. The stream identifier (QID) is used to index this region to provide the new PID value 25 which is subsequently exchanged for the original PID.