To support real-time multimedia applications in wireless packet networks, it is an essential challenge to provide seamless quality of service (QoS) to mobile users. In this paper, we address the problem of real-time multimedia multicast in cellular networks, and present our solution to avoid large QoS fluctuations during handoffs. Specifically, during a multicast session, a mobile host may experience varying packet delay, delay jitter, and channel error when it moves from one cell to another. It is thus desirable that these location-dependent QoS parameters appear as seamless as possible to mobile hosts. We present protocols to achieve a degree of transmission synchronization among multiple cells, so that the delays and delay jitters of each packet to all subscribing mobile hosts do not vary substantially. In addition, we apply Forward Error Correction technique to recover the QoS-mandatory packets from wireless channel errors. We show through analysis and simulation that the mobile hosts will experience brief, smooth, and low packet loss rate handoffs.