RTP Audio Video Profiles
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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 kbit/s |
| 1 | 1016 | 8000 | CELP Audio 4.8 kbit/s |
| 2 | G721 | 8000 | ITU G721 ADPCM Audio 32 kbit/s |
| 3 | GSM | 8000 | European GSM Audio 13 kbit/s |
| 5 | DVI4 | 8000 | DVI ADPCM Audio 32 kbit/s |
| 6 | DVI4 | 16000 | DVI ADPCM 64 kbit/s |
| 7 | LPC | 8000 | Experimental LPC Audio |
| 8 | PCMA | 8000 | ITU G.711 PCM A-Law Audio 64 kbit/s |
| 9 | G722 | 8000 | ITU G.722 Audio |
| 10 | L16 | 44100 | Linear 16-bit Audio 705.6 kbit/s |
| 11 | L16 | 44100 | Linear 16-bit Stereo Audio 1411.2 kbit/s |
| 14 | MPA | 90000 | MPEG-I or MPEG-II Audio Only |
| 15 | G728 | 8000 | ITU G.728 Audio 16 kbit/s |
| 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 kbit/s [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 is also contained in the SDP a=rtpmap: field, which is why the attribute is optional.
