To fairly allocate network bandwidth for different streams and to achieve a smooth quality between different video sequences are two key issues in multi-stream applications. In this paper, a new joint rate control scheme for multiple video streams based on game theory is proposed. We achieve a fair rate allocation in video quality between different sequences by Nash Bargaining theory under the constraints of buffer and bandwidth. Also, by grouping all the different sequences' frames within the same timeslot into a coalition, we can avoid the fluctuation in a sequence by bargaining between current coalition and remaining coalitions. Some experiments have been conducted to verify the proposed method.