This paper addresses the transport of real-time multimedia traffic generated by MPEG-2 applications over ATM best effort services (ABR, UBR+). To cope with network congestion and the unreliability of the ATM Adaptation Layer type 5 (AAL5), we propose a new Service Specific Convergence Sublayer for AudioVisual applications. The proposed AV-SSCS includes adaptive Forward Data Error Correction (FEC) based on Reed-Solomon and Parity Codes. With respect to network load and video packet loss ratio measured at the destination, the source can dynamically increase or reduce the FEC efficiency (i.e. the amount of data redundancy) to provide a higher protection to the video packet or a better use of the shared bandwidth respectively.