On distributed multimedia systems, we have been able to communicate with each others by using audio and video streams. If we can use super high speed network we may construct intercommunication environments by high quality video multicast streams such as DV (Digital Video) that uses about 30Mbps per a stream. Moreover, if translator and mixer functions defined by RTP are available on the intercommunication environments, it is able to transcode the high quality video streams into another format of stream. We can get usefulness peer-to-peer communication environments. 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 on demand transcoding functions with relocatable decision method. In this paper we propose a mobile agent based novel middleware system that realizes media processing and session management by using mobile agents.