A sample sequence ΔS similar to a first or last sample sequence of the current frame is extracted from its samples SFC and concatenated, as an alternative sample sequence AS, to each of the front and back of the current frame, and the current frame with the alternative sample sequence concatenated thereto is subjected to filtering or prediction coding to obtain processing result SOU of the current frame. In the case of prediction coding, auxiliary information, which indicates which part of the current frame was used as the alternative sample sequence, is also output. By this, filtering, autoregressive prediction coding and decoding, which require processing extending over preceding and succeeding frames as in an interpolation filter, can be concluded in the current frame with substantially no degradation of the continuity and coding efficient of the reconstructed signal.