RFC 6363 describes a framework for using Forward Error Correction (FEC) codes with applications in public and private IP networks to provide protection against packet loss. The framework supports applying FEC to arbitrary packet flows over unreliable transport and is primarily intended for real-time, or streaming, media. However FECFRAME as per RFC 6363 is restricted to block FEC codes. The present document extends FECFRAME to support FEC Codes based on a sliding encoding window, in addition to Block FEC Codes, in a backward compatible way. During multicast/broadcast real-time content delivery, the use of sliding window codes significantly improves robustness in harsh environments, with less repair traffic and lower FEC-related added latency.