A system and method for multiplexing and remultiplexing whereby multiplexed programs from an input stream are only demultiplexed if they are to be copied or modified locally. Any multiplexed programs which are part of an input stream and which are intended to be part of the output stream are not demultiplexed but are simply passed along to be added to the transport stream with other multiplexed programs. A further inventive aspect comprises a multiplexer apparatus and process whereby dynamic bit rate adjustment is applied to eliminate the need to recalculate timebase information for altered streams.