In this paper, we propose an application layer multicast protocol called Emma/QoS. Emma/QoS manages multiple multicast video streaming flows in a fully distributed manner so that the user gain in receiving those flows can be maximized. Emma/QoS assumes that each end-host is capable of filtering streaming flows when relaying them to the other end-hosts. Using this functionality, Emma/QoS (a) accommodates a request of a new video source by degrading the bit-rates of the existing video streams, and (b) adjusts their transmission rates according to given user benefit functions, which can be application-specific. Simulation results have shown the efficiency of Emma/QoS.