When a distributed MPEG player system is transmitting MPEG video streams over an open network, like the Internet, the system usually has no control on the network traffic. We define the quality of service (QoS) for video transmissions in an adaptive mechanism, and we propose a priority feedback mechanism with QoS Control (PFB-QoS) for a distributed MPEG player system. With the feedback signal coming from each client and our predefined priority mapping functions, the current status and priority of each client can be obtained. With such information, the video server will adapt to the dynamic changes in the network and make efforts to maintain the QoS requirement for each client under the current network constraints. From our preliminary experiments, we find that when a video server is serving multiple clients where every client can demand a different QoS, the use of a priority feedback mechanism can effectively maintain the committed quality of service.