This paper proposes a semi-reliable multicast protocol that evaluates the necessity of retransmitting lost packets, taking into account the priority associated to each lost packet. The protocol relies on the neighboring receivers for retransmitting lost packets, resulting in much faster recovery. This paper also demonstrates how the proposed protocol is able to increase the quality of video streams transmitted over the Internet, employing knowledge on the transmitted MPEG frames to drive the recovery when the packet containing the frame is lost.