RTP payload formats

The use of profiles enables RTP to be an extremely general media transport protocol. The current audio video profiles defined by RFC 3551 are listed in Table. The profile document makes the following specifications for RTP:

UDP is used for underlying transport;
RTP port numbers are always even, the corresponding RTCP port number is the next highest port, always an odd number;
No header extensions are used.

RTP/AVP Audio and Video Payload Types

Payload	Codec	Clock	Description
0	PCMU	8000	ITU G.711 PCM µ-Law Audio 64 Kbps
1	1016	8000	CELP Audio 4.8 Kbps
2	G721	8000	ITU G721 ADPCM Audio 32 Kbps
3	GSM	8000	European GSM Audio 13 Kbps
5	DVI4	8000	DVI ADPCM Audio 32 Kbps
6	DVI4	16000	DVI ADPCM 64 Kbps
7	LPC	8000	Experimental LPC Audio
8	PCMA	8000	ITU G.711 PCM A-Law Audio 64 Kbps
9	G722	8000	ITU G.722 Audio
10	L16	44100	Linear 16-bit Audio 705.6 Kbps
11	L16	44100	Linear 16-bit Stereo Audio 1411.2 Kbps
14	MPA	90000	MPEG-I or MPEG-II Audio Only
15	G728	8000	ITU G.728 Audio 16 Kbps
25	CELB	90000	CelB Video
26	JBEG	90000	JBEG Video
28	NV	90000	nv Video
31	H261	90000	ITU H.261 Video
32	MPV	90000	MPEG-I and MPEG-II Video
33	MP2T	90000	MPEG-II transport stream Video
dynamic	iLBC	—	Internet low bit rate 15 Kbps [6]
dynamic	AMR	—	Adaptive Multirate Codec [12]

For each of the profiles listed in Table, the profile document lists details of the codec, or a reference for the details is provided. Payloads in the range 96–127 can be defined dynamically during a session. The minimum payload support is defined as 0 (PCMU) and 5 (DVI4). The document recommends dynamically assigned port numbers, although 5004 and 5005 have been registered for use of the profile and can be used instead. The standard also describes the process of registering new payload types with IANA. There are other references for a tutorial description of many of these audio codecs and video codecs.
The information in the first three columns of Table 7.4 is also contained in the SDP a=rtpmap: field, which is why the attribute is optional.