So far, we have proposed Flexible Multimedia System (FMS) that is able to guarantee end-to-end QoS according to priority of parameters and consensus policy. On interconnected computer networks we can communicate with each other using realtime media such as audio and video by distributed multimedia system that can integrate various realtime and discrete media data. The multimedia system is required to realize end-to-end quality of service (QoS) guarantee functions. When users communicate with each other on interconnected different bandwidth networks, if the system can use translator or mixer functions that are defined by RTP, it will be able to guarantee more flexible QoS considering to wide band through narrow band networks. In addition, the system is able to organize various multimedia services dynamically. The FMS is mobile agent based system, therefore the system will be able to organize translator or mixer dynamically. In this paper, we discuss about QoS guarantee functions using mobile agent and re-design our prototype system to use mobile transcoding functions for flexible multimedia communication.