On intercommunication environments, if we can use transcoding functions that include translator and mixer functions defined by RTP, it is able to transcode a media stream format into another stream format. Media transcoding functions are usefulness for intercommunication on heterogeneous computer networks. However, it is difficult for us to prepare the suitable transcoding node in advance because the required intercommunication environments are not always static. Accordingly, we should consider dynamic transcoding functions with relocatable decision methods. In this paper we propose a novel middleware system that realizes dynamic transcoding functions by extended media stream.