This paper addresses the problem of choosing the optimal layer rate according to the type of multicast applications in multi-layered multicast applications to improve global video quality. Due to various types of applications, it introduces a global quality index (GQI) that characterizes the density of satisfied receivers (the degradation at the receivers), the amount of allocated network bandwidth and the stability of the quality of the receivers. These metrics compose the unified metric GQI that can be adjusted according to the type of the multicast applications. Simulation results show that...