1.8 Vendor-Extensible Fields
The standard method for selecting codecs in the RTPME protocol is through payload types. [RFC3551] provides a default mapping for audio and video codecs that includes a range from hexadecimal 0x60 to 0x7F to be used for dynamic codec mapping. For each RTPME protocol session using a dynamically mapped codec, a mapping between a number inside this range and a specific codec MUST be negotiated through non-RTP means (for example, through SDP). Although there are no reserved or assigned numbers within this dynamic payload type range, some codecs are typically mapped to specific payload types. Some examples of dynamic payload type conventions can be found in section 2.2.1 of this document.