RTP_audio_video_profile

RTP payload formats

RTP payload formats

Multimedia information signaling

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.

More information Payload type (PT), Name ...
  1. [N 1]
    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.
  2. [N 2]
    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]
  3. [N 3]
    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 maxplaybackrate and sprop-maxcapturerate parameters in SDP can be used to indicate hints/preferences about the maximum sampling rate to encode/decode.
  4. [N 4]
    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

  • RFC 4103, RTP Payload Format for Text Conversation

MIDI payload

See also

References

  1. [1]
    RFC 3551, RTP Profile for Audio and Video Conferences with Minimal Control, H. Schulzrinne, S. Casner, The Internet Society (July 2003).
  2. [2]
    "RFC 2586 - The Audio/L16 MIME content type". May 1999. Retrieved 2010-03-16.
  3. [3]
    "RFC 3108 - Conventions for the use of the Session Description Protocol (SDP) for ATM Bearer Connections". May 2001. Retrieved 2010-03-16.
  4. [4]
    "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.
  5. [5]
    XIL Programmer's Guide, Chapter 22 "CellB Codec". August 1997. Retrieved on 2014-07-19.
  6. [6]
    nv - network video on Henning Schulzrinne's website, Network Video on The University of Toronto's website, Retrieved on 2009-07-09.
  7. [7]
    Ron Frederick Github with source code
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