This document defines new RTP payload formats for the Forward Error
Correction (FEC) packets that are generated by the non-interleaved and
interleaved parity codes from source media encapsulated in RTP. These
parity codes are systematic codes (Flexible FEC, or "FLEX FEC"), where
a number of FEC repair packets are generated from a set of source
packets from one or more source RTP streams. These FEC repair packets
are sent in a redundancy RTP stream separate from the source RTP
stream(s) that carries the source packets. RTP source packets that
were lost in transmission can be reconstructed using the source and
repair packets that were received. The non-interleaved and interleaved
parity codes which are defined in this specification offer a good
protection against random and bursty packet losses, respectively, at a
cost of complexity. The RTP payload formats that are defined in this
document address scalability issues experienced with the earlier
specifications, and offer several improvements. Due to these changes,
the new payload formats are not backward compatible with earlier
specifications, but endpoints that do not implement this specification
can still work by simply ignoring the FEC repair packets.