Abstract: A data stream processing device for processing a succession of information datagrams from multiple data streams, each datagram comprising a payload and an identifier identifying the data stream of which the datagram forms part, the device comprising: a storer for storing an indication of which of the data streams are required for use; a memory; and a datagram processor connected to the storer and the memory and arranged for: receiving incoming datagrams, reading the identifiers of received datagrams and thereby identifying the data stream of which each datagram forms part, and storing in the memory received datagrams that form part of a data stream required for use, and if successively received datagrams that form part of a data stream required for use are interspersed by one or more received datagrams that do not form part of a data stream required for use, storing an indication of the spacing between the said successively received datagrams.