Natural sharing of informative media contents is a key service in collaborative and smart work that flexibly conducts remote operations and communicates with remote co-workers in home offices and smart work centers. For collaborative and smart work, we need to carefully disseminate media services tailored for each participating site in order to naturally exchange shared contents between participants. In this paper, we present a centralized mediation approach to fairly improve the qualities of shared videos in multi-producer multi-consumer environment. The proposed approach carries out progressive improvement of end-user quality and efficient placement of transcoders by balancing the overall usage of computation and networking resources. Computer-simulated experiment results demonstrate that the proposed approach can find a feasible solution and improve the running time performance.