The Real-time Transport Protocol (RTP) specifies a general-purpose data format and network protocol for transmitting digital media streams on Internet Protocol (IP) networks. The details of media encoding, such as signal sampling rate, frame size and timing, are specified in an RTP payload format. The format parameters of the RTP payload are typically communicated between transmission endpoints with the Session Description Protocol (SDP), but other protocols, such as the Extensible Messaging and Presence Protocol (XMPP) may be used.
Audio and video payload types
RFC 3551, entitled RTP Profile for Audio and Video (RTP/AVP), specifies the technical parameters of payload formats for audio and video streams.
The standard also describes the process of registering new payload types with IANA; additional payload formats and payload types are defined in the following specifications:
- RFC 3551, Standard 65, RTP Profile for Audio and Video Conferences with Minimal Control
- RFC 4856, Media Type Registration of Payload Formats in the RTP Profile for Audio and Video Conferences
- RFC 3190, RTP Payload Format for 12-bit DAT Audio and 20- and 24-bit Linear Sampled Audio
- RFC 6184, RTP Payload Format for H.264 Video
- RFC 3640, RTP Payload Format for Transport of MPEG-4 Elementary Streams
- RFC 6416, RTP Payload Format for MPEG-4 Audio/Visual Streams
- RFC 2250, RTP Payload Format for MPEG1/MPEG2 Video
- RFC 7798, RTP Payload Format for High Efficiency Video Coding (HEVC)
- RFC 2435, RTP Payload Format for JPEG-compressed Video
- RFC 4587, RTP Payload Format for H.261 Video Streams
- RFC 2658, RTP Payload Format for PureVoice Audio Video
- RFC 4175, RTP Payload Format for Uncompressed Video
- RFC 7587, RTP Payload Format for the Opus Speech and Audio Codec
- RFC 9134, RTP Payload Format for JPEG XS
Payload identifiers 96–127 are used for payloads defined dynamically during a session. It is recommended to dynamically assign port numbers, although port numbers 5004 and 5005 have been registered for use of the profile when a dynamically assigned port is not required.
Applications should always support PCMU (payload type 0); previously, DVI4 (payload type 5) was also recommended, but this was removed in 2013 by RFC 7007.
| Payload type (PT) | Name | Type | No. of channels | Clock rate (Hz)[note 1] | Frame size (byte) | Default packet interval (ms) | Description | References |
|---|---|---|---|---|---|---|---|---|
| 0 | PCMU | audio | 1 | 8000 | any | 20 | ITU-T G.711 PCM μ-Law audio 64 kbit/s | RFC 3551 |
| 1 | reserved (previously FS-1016 CELP) | audio | 1 | 8000 | reserved, previously FS-1016 CELP audio 4.8 kbit/s | RFC 3551, previously RFC 1890 | ||
| 2 | reserved (previously G721 or G726-32) | audio | 1 | 8000 | reserved, previously ITU-T G.721 ADPCM audio 32 kbit/s or ITU-T G.726 audio 32 kbit/s | RFC 3551, previously RFC 1890 | ||
| 3 | GSM | audio | 1 | 8000 | 20 | 20 | European GSM Full Rate audio 13 kbit/s (GSM 06.10) | RFC 3551 |
| 4 | G723 | audio | 1 | 8000 | 30 | 30 | ITU-T G.723.1 audio | RFC 3551 |
| 5 | DVI4 | audio | 1 | 8000 | any | 20 | IMA ADPCM audio 32 kbit/s | RFC 3551 |
| 6 | DVI4 | audio | 1 | 16000 | any | 20 | IMA ADPCM audio 64 kbit/s | RFC 3551 |
| 7 | LPC | audio | 1 | 8000 | any | 20 | Experimental Linear Predictive Coding audio 5.6 kbit/s | RFC 3551 |
| 8 | PCMA | audio | 1 | 8000 | any | 20 | ITU-T G.711 PCM A-Law audio 64 kbit/s | RFC 3551 |
| 9 | G722 | audio | 1 | 8000[note 2] | any | 20 | ITU-T G.722 audio 64 kbit/s | RFC 3551 - Page 14 |
| 10 | L16 | audio | 2 | 44100 | any | 20 | Linear PCM 16-bit Stereo audio 1411.2 kbit/s,[2][3][4] uncompressed | RFC 3551, Page 27 |
| 11 | L16 | audio | 1 | 44100 | any | 20 | Linear PCM 16-bit audio 705.6 kbit/s, uncompressed | RFC 3551, Page 27 |
| 12 | QCELP | audio | 1 | 8000 | 20 | 20 | Qualcomm Code Excited Linear Prediction | RFC 2658, RFC 3551 |
| 13 | CN | audio | 1 | 8000 | Comfort noise. Payload type used with audio codecs that do not support comfort noise as part of the codec itself such as G.711, G.722.1, G.722, G.726, G.727, G.728, GSM 06.10, Siren, and RTAudio. | RFC 3389 | ||
| 14 | MPA | audio | 1, 2 | 90000 | 8–72 | MPEG-1 or MPEG-2 audio only | RFC 3551, RFC 2250 | |
| 15 | G728 | audio | 1 | 8000 | 2.5 | 20 | ITU-T G.728 audio 16 kbit/s | RFC 3551 |
| 16 | DVI4 | audio | 1 | 11025 | any | 20 | IMA ADPCM audio 44.1 kbit/s | RFC 3551 |
| 17 | DVI4 | audio | 1 | 22050 | any | 20 | IMA ADPCM audio 88.2 kbit/s | RFC 3551 |
| 18 | G729 | audio | 1 | 8000 | 10 | 20 | ITU-T G.729 and G.729a audio 8 kbit/s; Annex B is implied unless the annexb=no parameter is used |
RFC 3551, Page 20, RFC 3555, Page 15 |
| 19 | reserved (previously CN) | audio | reserved, previously comfort noise | RFC 3551 | ||||
| 25 | CELLB | video | 90000 | Sun CellB video[5] | RFC 2029 | |||
| 26 | JPEG | video | 90000 | JPEG video | RFC 2435 | |||
| 28 | nv | video | 90000 | Xerox PARC's Network Video (nv)[6][7] | RFC 3551, Page 32 | |||
| 31 | H261 | video | 90000 | ITU-T H.261 video | RFC 4587 | |||
| 32 | MPV | video | 90000 | MPEG-1 and MPEG-2 video | RFC 2250 | |||
| 33 | MP2T | audio/video | 90000 | MPEG-2 transport stream | RFC 2250 | |||
| 34 | H263 | video | 90000 | H.263 video, first version (1996) | RFC 3551, RFC 2190 | |||
| 72–76 | reserved | reserved because RTCP packet types 200–204 would otherwise be indistinguishable from RTP payload types 72–76 with the marker bit set | RFC 3550, RFC 3551 | |||||
| 77–95 | unassigned | note that RTCP packet type 207 (XR, Extended Reports) would be indistinguishable from RTP payload types 79 with the marker bit set | RFC 3551, RFC 3611 | |||||
| dynamic | H263-1998 | video | 90000 | H.263 video, second version (1998) | RFC 3551, RFC 4629, RFC 2190 | |||
| dynamic | H263-2000 | video | 90000 | H.263 video, third version (2000) | RFC 4629 | |||
| dynamic (or profile) | H264 AVC | video | 90000 | H.264 video (MPEG-4 Part 10) | RFC 6184, previously RFC 3984 | |||
| dynamic (or profile) | H264 SVC | video | 90000 | H.264 video | RFC 6190 | |||
| dynamic (or profile) | H265 | video | 90000 | H.265 video (HEVC) | RFC 7798 | |||
| dynamic (or profile) | theora | video | 90000 | Theora video | draft-barbato-avt-rtp-theora | |||
| dynamic | iLBC | audio | 1 | 8000 | 20, 30 | 20, 30 | Internet low Bitrate Codec 13.33 or 15.2 kbit/s | RFC 3952 |
| dynamic | PCMA-WB | audio | 1 | 16000 | 5 | ITU-T G.711.1 A-law | RFC 5391 | |
| dynamic | PCMU-WB | audio | 1 | 16000 | 5 | ITU-T G.711.1 μ-law | RFC 5391 | |
| dynamic | G718 | audio | 32000 (placeholder) | 20 | ITU-T G.718 | draft-ietf-payload-rtp-g718 | ||
| dynamic | G719 | audio | (various) | 48000 | 20 | ITU-T G.719 | RFC 5404 | |
| dynamic | G7221 | audio | 16000, 32000 | 20 | ITU-T G.722.1 and G.722.1 Annex C | RFC 5577 | ||
| dynamic | G726-16 | audio | 1 | 8000 | any | 20 | ITU-T G.726 audio 16 kbit/s | RFC 3551 |
| dynamic | G726-24 | audio | 1 | 8000 | any | 20 | ITU-T G.726 audio 24 kbit/s | RFC 3551 |
| dynamic | G726-32 | audio | 1 | 8000 | any | 20 | ITU-T G.726 audio 32 kbit/s | RFC 3551 |
| dynamic | G726-40 | audio | 1 | 8000 | any | 20 | ITU-T G.726 audio 40 kbit/s | RFC 3551 |
| dynamic | G729D | audio | 1 | 8000 | 10 | 20 | ITU-T G.729 Annex D | RFC 3551 |
| dynamic | G729E | audio | 1 | 8000 | 10 | 20 | ITU-T G.729 Annex E | RFC 3551 |
| dynamic | G7291 | audio | 16000 | 20 | ITU-T G.729.1 | RFC 4749 | ||
| dynamic | GSM-EFR | audio | 1 | 8000 | 20 | 20 | ITU-T GSM-EFR (GSM 06.60) | RFC 3551 |
| dynamic | GSM-HR-08 | audio | 1 | 8000 | 20 | ITU-T GSM-HR (GSM 06.20) | RFC 5993 | |
| dynamic (or profile) | AMR | audio | (various) | 8000 | 20 | Adaptive Multi-Rate audio | RFC 4867 | |
| dynamic (or profile) | AMR-WB | audio | (various) | 16000 | 20 | Adaptive Multi-Rate Wideband audio (ITU-T G.722.2) | RFC 4867 | |
| dynamic (or profile) | AMR-WB+ | audio | 1, 2 or omit | 72000 | 13.3–40 | Extended Adaptive Multi Rate – WideBand audio | RFC 4352 | |
| dynamic (or profile) | vorbis | audio | (various) | (various) | Vorbis audio | RFC 5215 | ||
| dynamic (or profile) | opus | audio | 1, 2 | 48000[note 3] | 2.5–60 | 20 | Opus audio | RFC 7587 |
| dynamic (or profile) | speex | audio | 1 | 8000, 16000, 32000 | 20 | Speex audio | RFC 5574 | |
| dynamic | mpa-robust | audio | 1, 2 | 90000 | 24–72 | Loss-Tolerant MP3 audio | RFC 5219 (previously RFC 3119) | |
| dynamic (or profile) | MP4A-LATM | audio | 90000 or others | MPEG-4 Audio (includes AAC) | RFC 6416 (previously RFC 3016) | |||
| dynamic (or profile) | MP4V-ES | video | 90000 or others | MPEG-4 Visual | RFC 6416 (previously RFC 3016) | |||
| dynamic (or profile) | mpeg4-generic | audio/video | 90000 or other | MPEG-4 Elementary Streams | RFC 3640 | |||
| dynamic | VP8 | video | 90000 | VP8 video | RFC 7741 | |||
| dynamic | VP9 | video | 90000 | VP9 video | draft-ietf-payload-vp9 | |||
| dynamic | L8 | audio | (various) | (various) | any | 20 | Linear PCM 8-bit audio with 128 offset | RFC 3551 Section 4.5.10 and Table 5 |
| dynamic | DAT12 | audio | (various) | (various) | any | 20 (by analogy with L16) | IEC 61119 12-bit nonlinear audio | RFC 3190 Section 3 |
| dynamic | L16 | audio | (various) | (various) | any | 20 | Linear PCM 16-bit audio | RFC 3551 Section 4.5.11, RFC 2586 |
| dynamic | L20 | audio | (various) | (various) | any | 20 (by analogy with L16) | Linear PCM 20-bit audio | RFC 3190 Section 4 |
| dynamic | L24 | audio | (various) | (various) | any | 20 (by analogy with L16) | Linear PCM 24-bit audio | RFC 3190 Section 4 |
| dynamic | raw | video | 90000 | Uncompressed Video | RFC 4175 | |||
| dynamic | ac3 | audio | (various) | 32000, 44100, 48000 | Dolby AC-3 audio | RFC 4184 | ||
| dynamic | eac3 | audio | (various) | 32000, 44100, 48000 | Enhanced AC-3 audio | RFC 4598 | ||
| dynamic | t140 | text | 1000 | Text over IP | RFC 4103 | |||
| dynamic | EVRC EVRC0 EVRC1 |
audio | 8000 | EVRC audio | RFC 4788 | |||
| dynamic | EVRCB EVRCB0 EVRCB1 |
audio | 8000 | EVRC-B audio | RFC 4788 | |||
| dynamic | EVRCWB EVRCWB0 EVRCWB1 |
audio | 16000 | EVRC-WB audio | RFC 5188 | |||
| dynamic | jpeg2000 | video | 90000 | JPEG 2000 video | RFC 5371 | |||
| dynamic | UEMCLIP | audio | 8000, 16000 | UEMCLIP audio | RFC 5686 | |||
| dynamic | ATRAC3 | audio | 44100 | ATRAC3 audio | RFC 5584 | |||
| dynamic | ATRAC-X | audio | 44100, 48000 | ATRAC3+ audio | RFC 5584 | |||
| dynamic | ATRAC-ADVANCED-LOSSLESS | audio | (various) | ATRAC Advanced Lossless audio | RFC 5584 | |||
| dynamic | DV | video | 90000 | DV video | RFC 6469 (previously RFC 3189) | |||
| dynamic | BT656 | video | ITU-R BT.656 video | RFC 3555 | ||||
| dynamic | BMPEG | video | Bundled MPEG-2 video | RFC 2343 | ||||
| dynamic | SMPTE292M | video | SMPTE 292M video | RFC 3497 | ||||
| dynamic | RED | audio | Redundant Audio Data | RFC 2198 | ||||
| dynamic | VDVI | audio | Variable-rate DVI4 audio | RFC 3551 | ||||
| dynamic | MP1S | video | MPEG-1 Systems Streams video | RFC 2250 | ||||
| dynamic | MP2P | video | MPEG-2 Program Streams video | RFC 2250 | ||||
| dynamic | tone | audio | 8000 (default) | tone | RFC 4733 | |||
| dynamic | telephone-event | audio | 8000 (default) | DTMF tone | RFC 4733 | |||
| dynamic | aptx | audio | 2 – 6 | (equal to sampling rate) | 4000 ÷ sample rate | 4[note 4] | aptX audio | RFC 7310 |
| dynamic | jxsv | video | 90000 | JPEG XS video | RFC 9134 |
- ↑ The "clock rate" is the rate at which the timestamp in the RTP header is incremented, which need not be the same as the codec's sampling rate. For instance, video codecs typically use a clock rate of 90000 so their frames can be more precisely aligned with the RTCP NTP timestamp, even though video sampling rates are typically in the range of 1–60 samples per second.
- ↑ Although the sampling rate for G.722 is 16000, its clock rate is 8000 to remain backwards compatible with RFC 1890, which incorrectly used this value.[1]
- ↑ Because Opus can change sampling rates dynamically, its clock rate is fixed at 48000, even when the codec will be operated at a lower sampling rate. The
maxplaybackrateandsprop-maxcapturerateparameters in SDP can be used to indicate hints/preferences about the maximum sampling rate to encode/decode. - ↑ For aptX, the packetization interval must be rounded down to the nearest packet interval that can contain an integer number of samples. So at sampling rates of 11025, 22050, or 44100, a packetization rate of "4" is rounded down to 3.99.
Text messaging payload
MIDI payload
- RFC 6295, RTP Payload Format for MIDI
- RFC 4696, An Implementation Guide for RTP MIDI
See also
References
- ↑ RFC 3551, RTP Profile for Audio and Video Conferences with Minimal Control, H. Schulzrinne, S. Casner, The Internet Society (July 2003).
- ↑ "RFC 2586 - The Audio/L16 MIME content type". May 1999. Retrieved 2010-03-16.
- ↑ "RFC 3108 - Conventions for the use of the Session Description Protocol (SDP) for ATM Bearer Connections". May 2001. Retrieved 2010-03-16.
- ↑ "RFC 4856 - Media Type Registration of Payload Formats in the RTP Profile for Audio and Video Conferences - Registration of Media Type audio/L16". March 2007. Retrieved 2010-03-16.
- ↑ XIL Programmer's Guide, Chapter 22 "CellB Codec". August 1997. Retrieved on 2014-07-19.
- ↑ nv - network video on Henning Schulzrinne's website, Network Video on The University of Toronto's website, Retrieved on 2009-07-09.
- ↑ Ron Frederick Github with source code
External links
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