Multicast distribution of multimedia streams is an important component of many existing and future networked services. These services are characterized by the integrated processing of different media types, such as audio and video. Often, different multimedia streams must be played out in a synchronized way. Due to the asynchronous nature of networks, some problems can disrupt synchronization such as delay jitter and different initial playback times. In this paper, we propose a method consisting of intra-stream and inter-client synchronization mechanisms. It allows different members of a multicast group to playback media units at the same time and in a continuous manner. The mechanism can be used in networks having unknown delay bounds. It allows to receivers to be synchronized for media unit playbacks. To do this, we use feedback messages to the source and buffer management. However, there is no assumption about clock synchronization and messages are not time-stamped.