Abstract: A transcoder for the conversion of video signals between a first and a second coding scheme employing motion compensation comprises a decoder (28) for decoding a received data stream encoded according to a first coding scheme and an encoder (30) for encoding a data stream from the decoder into a data stream according to a second coding scheme. The decoder (28) extracts motion vectors from the received data stream and passes them (42) to the data stream of the encoder, so avoiding the recalculation of the motion vectors. Drift compensation means (52-64; 70-78) may be provided to compensate for any resulting drift after a picture frame.

Abstract: A transcoder converts a received data stream encoded according to a first coding scheme to a data stream coded according to a second coding schem. The schemes specify a first and a a second maximum amount of jitter that may be present in the encoded data streams, respectively. The transcoder includes a decoder section and an encoder section and is operated such that the data stream received by the encoder section has a non-zero amount of jitter and the encoder section produces a coded data stream having an amount of jitter which is less than or equal to the second maximum amount of jitter. By operating the transcoder to provide a decoded video data stream to the encoder section which retains a degree of jitter relative to the oriignal video signal, the buffer requirements can be minimized therefore providing reduced buffeer delay and hence a transcoder with smaller buffer delay than previously obtainable.