A data transport device for transporting a data stream, the device including: a data stream processing unit for receiving an input data stream including a plurality of data items, performing processing in dependence on the content of the items and forming an output data stream including at least some of the data items; and a data item injection unit including a memory for storing a plurality of injection data items and associated with each injection data item an injection action, and an injection processor arranged to retrieve the injection action for each of the injection data items in turn and in dependence on the retrieved injection action to inject the associated injection data item into the output data stream.