http://www.rfc-editor.org/rfc/rfc4348.txt
RFC 4348: Real-Time Transport Protocol (RTP) Payload Format for the Variable-Rate Multimode Wideband (VMR-WB) Audio Codec, S. Ahmadi2006-01-01T23:00:00-00:00VMR-WB is a variable-rate multimode wideband speech codec that has a number of operating modes, one of which is interoperable with AMR-WB (i.e., RFC 3267) audio codec at certain rates. Therefore, provisions have been made in this document to facilitate and simplify data packet exchange between VMR-WB and AMR-WB in the interoperable mode with no transcoding function involved. [STANDARDS-TRACK]