The RTP audio/video profile (RTP/AVP) is a profile for Real-time Transport Protocol (RTP) that specifies the technical parameters of audio and video streams. RTP specifies a general-purpose data format, but doesn't specify how encoded data should utilize the features of RTP (what payload type value to put in the RTP header, what sampling rate and clock rate [the rate at which the RTP timestamp increments] to use, etc.). An RTP profile specifies these details. The RTP audio/video profile specifies a mapping of specific audio and video codecs and their sampling rates to RTP payload types and clock rates, and how to encode each data format as an RTP data payload, as well as specifying how to describe these mappings using Session Description Protocol (SDP).
RTP/AVP audio and video payload types
RFC 3551 lists details of the payload format, or a reference for the details is provided. Payload identifiers 96–127 are used for payloads defined dynamically during a session. The document recommends dynamically assigned port numbers, although port numbers 5004 and 5005 have been registered for use of the profile when a dynamically assigned port is not required. The standard also describes the process of registering new payload types with IANA.
Applications operating under this profile should always support PCMU (payload type 0). Previously, DVI4 (payload type 5) was also recommended, but this recommendation was removed in August 2013 by RFC 7007 because "many RTP deployments do not support DVI4, and there is little reason to use it when much more modern codecs are available."