Real-time audio and video conferencing and communication applications that use the Real-time Transport Protocol

Real-time Transport Protocol

The Real-time Transport Protocol defines a standardized packet format for delivering audio and video over IP networks. RTP is used extensively in communication and entertainment systems that involve streaming media, such as telephony, video teleconference applications, television services and...

 (RTP) employ Session Description Protocol

Session Description Protocol

The Session Description Protocol is a format for describing streaming media initialization parameters. The IETF published the original specification as an IETF Proposed Standard in April 1998, and subsequently published a revised specification as an IETF Proposed Standard as RFC 4566 in July...

 (SDP) to describe the media streams carried in a multi-media session. This description format specifies the technical parameters of the media streams. Such a set of RTP parameters of the media stream and its compression or encoding methods is known as a media profile, or RTP audio video profile (RTP/AVP). Each profile is identified by a standardized payload type identifier.

RTP/AVP audio and video payload types

Payload type (PT)	Name	Type	No. of channels	Clock rate (Hz)	Description	References
0	PCMU	audio	1	8000	ITU-T G.711 G.711 G.711 is an ITU-T standard for audio companding. It is primarily used in telephony. The standard was released for usage in 1972. Its formal name is Pulse code modulation of voice frequencies. It is required standard in many technologies, for example in H.320 and H.323 specifications. It can also...  PCM µ-Law Audio 64 kbit/s	RFC 3551
1	reserved (previously 1016)	audio	1	8000	reserved, previously CELP Audio 4.8 kbit/s	RFC 3551, previously RFC 1890
2	reserved (previously G721)	audio	1	8000	reserved, previously ITU-T G.721 ADPCM Audio 32 kbit/s	RFC 3551, previously RFC 1890
3	GSM	audio	1	8000	European GSM Full Rate Audio 13 kbit/s (GSM 06.10)	RFC 3551
4	G723	audio	1	8000	ITU-T G.723.1 G.723.1 G.723.1 is an audio codec for voice that compresses voice audio in 30 ms frames. An algorithmic look-ahead of 7.5 ms duration means that total algorithmic delay is 37.5 ms...	RFC 3551
5	DVI4	audio	1	8000	IMA Interactive Multimedia Association The Interactive Multimedia Association was an industry association which developed a set of audio algorithms. The most important is the ADPCM algorithm which is in use by Apple and Microsoft....  ADPCM Audio 32 kbit/s	RFC 3551
6	DVI4	audio	1	16000	IMA Interactive Multimedia Association The Interactive Multimedia Association was an industry association which developed a set of audio algorithms. The most important is the ADPCM algorithm which is in use by Apple and Microsoft....  ADPCM 64 kbit/s	RFC 3551
7	LPC	audio	1	8000	Experimental Linear Predictive Coding Linear predictive coding Linear predictive coding is a tool used mostly in audio signal processing and speech processing for representing the spectral envelope of a digital signal of speech in compressed form, using the information of a linear predictive model...  Audio	RFC 3551
8	PCMA	audio	1	8000	ITU-T G.711 PCM A-Law Audio 64 kbit/s	RFC 3551
9	G722	audio	1	8000	ITU-T G.722 G.722 G.722 is a ITU-T standard 7 kHz wideband speech codec operating at 48, 56 and 64 kbit/s. It was approved by ITU-T in November 1988. Technology of the codec is based on sub-band ADPCM ....  Audio	RFC 3551 - Page 14
10	L16	audio	2	44100	Linear PCM 16-bit Stereo Audio 1411.2 kbit/s, uncompressed	RFC 3551, Page 27
11	L16	audio	1	44100	Linear PCM 16-bit Audio 705.6 kbit/s, uncompressed	RFC 3551, Page 27
12	QCELP	audio	1	8000	Qualcomm Code Excited Linear Prediction QCELP Qualcomm code-excited linear prediction , also known as Qualcomm PureVoice, is a speech codec developed in 1994 by Qualcomm to increase the speech quality of the IS-96A codec earlier used in CDMA networks. It was later replaced with EVRC since it provides better speech quality with fewer bits...	RFC 2658, RFC 3551
13	CN	audio	1	8000	Comfort noise Comfort noise Comfort noise is synthetic background noise used in radio and wireless communications to fill the artificial silence in a transmission resulting from voice activity detection or from the audio clarity of modern digital lines....	RFC 3389
14	MPA	audio	1	90000	MPEG-1 MPEG-1 MPEG-1 is a standard for lossy compression of video and audio. It is designed to compress VHS-quality raw digital video and CD audio down to 1.5 Mbit/s without excessive quality loss, making video CDs, digital cable/satellite TV and digital audio broadcasting possible.Today, MPEG-1 has become...  or MPEG-2 MPEG-2 MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of lossy video compression and lossy audio data compression methods which permit storage and transmission of movies using currently available storage media and transmission...  Audio Only	RFC 3551, RFC 2250
15	G728	audio	1	8000	ITU-T G.728 G.728 G.728 is an ITU-T standard for speech coding operating at 16 kbit/s. It is officially described as Coding of speech at 16 kbit/s using low-delay code excited linear prediction....  Audio 16 kbit/s	RFC 3551
16	DVI4	audio	1	11025	IMA Interactive Multimedia Association The Interactive Multimedia Association was an industry association which developed a set of audio algorithms. The most important is the ADPCM algorithm which is in use by Apple and Microsoft....  ADPCM	RFC 3551
17	DVI4	audio	1	22050	IMA ADPCM	RFC 3551
18	G729	audio	1	8000	ITU-T G.729 G.729 G.729 is an audio data compression algorithm for voice that compresses digital voice in packets of 10 milliseconds duration. It is officially described as Coding of speech at 8 kbit/s using conjugate-structure algebraic code-excited linear prediction .Because of its low bandwidth requirements,...  and G.729a	RFC 3551, Page 20
25	CELB	video	1	90000	Sun Sun Microsystems Sun Microsystems, Inc. was a company that sold :computers, computer components, :computer software, and :information technology services. Sun was founded on February 24, 1982... 's CellB Video Encoding	RFC 2029
26	JPEG	video	1	90000	JPEG JPEG In computing, JPEG . The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality....  Video	RFC 2435
28	NV	video	1	90000	Xerox PARC Xerox PARC PARC , formerly Xerox PARC, is a research and co-development company in Palo Alto, California, with a distinguished reputation for its contributions to information technology and hardware systems.... 's Network Video (nv)	RFC 3551, Page 32
31	H261	video	1	90000	ITU-T H.261 H.261 H.261 is a ITU-T video coding standard, ratified in November 1988. It is the first member of the H.26x family of video coding standards in the domain of the ITU-T Video Coding Experts Group , and was the first video codec that was useful in practical terms.H.261 was originally designed for...  Video	RFC 4587
32	MPV	video	1	90000	MPEG-1 and MPEG-2 Video	RFC 2250
33	MP2T	audio/video	1	90000	MPEG-2 transport stream Video	RFC 2250
34	H263	video		90000	H.263 H.263 H.263 is a video compression standard originally designed as a low-bitrate compressed format for videoconferencing. It was developed by the ITU-T Video Coding Experts Group in a project ending in 1995/1996 as one member of the H.26x family of video coding standards in the domain of the ITU-T.H.263...  video, first version (1996)	RFC 3551, RFC 2190
dynamic	H263-1998	video		90000	H.263 H.263 H.263 is a video compression standard originally designed as a low-bitrate compressed format for videoconferencing. It was developed by the ITU-T Video Coding Experts Group in a project ending in 1995/1996 as one member of the H.26x family of video coding standards in the domain of the ITU-T.H.263...  video, second version (1998)	RFC 3551, RFC 4629, RFC 2190
dynamic	H263-2000	video		90000	H.263 H.263 H.263 is a video compression standard originally designed as a low-bitrate compressed format for videoconferencing. It was developed by the ITU-T Video Coding Experts Group in a project ending in 1995/1996 as one member of the H.26x family of video coding standards in the domain of the ITU-T.H.263...  video, third version (2000)	RFC 4629
dynamic (or profile)	H264	video		90000	H.264 video (MPEG-4 Part 10)	RFC 3984
dynamic (or profile)	theora	video		90000	Theora Theora Theora is a free lossy video compression format. It is developed by the Xiph.Org Foundation and distributed without licensing fees alongside their other free and open media projects, including the Vorbis audio format and the Ogg container....  video	draft-barbato-avt-rtp-theora-01
dynamic	iLBC	audio	1	—	Internet low Bitrate Codec ILBC Internet Low Bitrate Codec is an open source royalty-free narrowband speech codec, developed by Global IP Solutions formerly Global IP Sound . It was formerly licensed as a freeware with limited commercial use, but since 2011 it is available under an open source license as a part of the open...  13.33 or 15.2 kbit/s	RFC 3951
dynamic	PCMA-WB	audio		16000	ITU-T G.711.1 G.711 G.711 is an ITU-T standard for audio companding. It is primarily used in telephony. The standard was released for usage in 1972. Its formal name is Pulse code modulation of voice frequencies. It is required standard in many technologies, for example in H.320 and H.323 specifications. It can also... , A-law	RFC 5391
dynamic	PCMU-WB	audio		16000	ITU-T G.711.1 G.711 G.711 is an ITU-T standard for audio companding. It is primarily used in telephony. The standard was released for usage in 1972. Its formal name is Pulse code modulation of voice frequencies. It is required standard in many technologies, for example in H.320 and H.323 specifications. It can also... , µ-law	RFC 5391
dynamic	G718	audio		32000	ITU-T G.718 G.718 G.718 is an ITU-T recommendation embedded scalable speech and audio codec providing high quality narrowband speech over the lower bit rates and high quality wideband speech over the complete range of bit rates...	draft-ietf-avt-rtp-g718-03
dynamic	G719	audio	(various)	48000	ITU-T G.719 G.719 G.719 is an ITU-T standard audio codec providing high quality, moderate bit rate wideband audio coding at low computational load...	RFC 5404
dynamic	G7221	audio		16 or 32kHz	ITU-T G.722.1 G.722.1 G.722.1 is a licensed royalty-free ITU-T standard audio codec providing high quality, moderate bit rate wideband G.722.1 is a licensed royalty-free ITU-T standard audio codec providing high quality, moderate bit rate (24 and 32 kbit/s) wideband G.722.1 is a licensed royalty-free ITU-T standard...	RFC 5577
dynamic	G726-16	audio	1	8000	ITU-T G.726 G.726 G.726 is an ITU-T ADPCM speech codec standard covering the transmission of voice at rates of 16, 24, 32, and 40 kbit/s. It was introduced to supersede both G.721, which covered ADPCM at 32 kbit/s, and G.723, which described ADPCM for 24 and 40 kbit/s. G.726 also introduced a new...  audio with 16 kbit/s	RFC 3551
dynamic	G726-24	audio	1	8000	ITU-T G.726 audio with 24 kbit/s	RFC 3551
dynamic	G726-32	audio	1	8000	ITU-T G.726 audio with 32 kbit/s	RFC 3551
dynamic	G726-40	audio	1	8000	ITU-T G.726 audio with 40 kbit/s	RFC 3551
dynamic	G729D	audio	1	8000	ITU-T G.729 G.729 G.729 is an audio data compression algorithm for voice that compresses digital voice in packets of 10 milliseconds duration. It is officially described as Coding of speech at 8 kbit/s using conjugate-structure algebraic code-excited linear prediction .Because of its low bandwidth requirements,...  Annex D	RFC 3551
dynamic	G729E	audio	1	8000	ITU-T G.729 G.729 G.729 is an audio data compression algorithm for voice that compresses digital voice in packets of 10 milliseconds duration. It is officially described as Coding of speech at 8 kbit/s using conjugate-structure algebraic code-excited linear prediction .Because of its low bandwidth requirements,...  Annex E	RFC 3551
dynamic	G7291	audio		(various)	ITU-T G.729.1 G.729.1 G.729.1 is an 8-32 kbit/s embedded speech and audio codec providing bitstream interoperability with G.729, G.729 Annex A and G.729 Annex B. Its official name is G.729-based embedded variable bit rate codec: An 8-32 kbit/s scalable wideband coder bitstream interoperable with G.729.This codec has...	RFC 4749
dynamic	GSM-EFR	audio	1	8000	ITU-T GSM-EFR (GSM 06.60)	RFC 3551
dynamic	GSM-HR-08	audio	1	8000	ITU-T GSM-HR Half Rate Half Rate is a speech coding system for GSM, developed in the early 1990s.Since the codec, operating at 5.6 kbit/s, requires half the bandwidth of the Full Rate codec, network capacity for voice traffic is doubled, at the expense of audio quality. It is recommended to use this codec when the...  (GSM 06.20)	RFC 5993
dynamic (or profile)	AMR	audio	(various)	8000	Adaptive Multi-Rate Adaptive Multi-Rate The Adaptive Multi-Rate audio codec is a patented audio data compression scheme optimized for speech coding. AMR was adopted as the standard speech codec by 3GPP in October 1999 and is now widely used in GSM and UMTS...  audio	RFC 4867
dynamic (or profile)	AMR-WB	audio	(various)	16000	Adaptive Multi-Rate Wideband AMR-WB Adaptive Multi-Rate Wideband is a patented speech coding standard developed based on Adaptive Multi-Rate encoding, using similar methodology as Algebraic Code Excited Linear Prediction...  audio (ITU-T G.722.2)	RFC 4867
dynamic (or profile)	AMR-WB+	audio	1, 2 or omit	72000	Extended Adaptive Multi Rate – WideBand AMR-WB+ Extended Adaptive Multi-Rate – Wideband is an audio codec that extends AMR-WB. It adds support for stereo signals and higher sampling rates. Another main improvement is the use of transform coding additionally to ACELP. This greatly improves the generic audio coding...  audio	RFC 4352
dynamic (or profile)	vorbis	audio	(various)	from 8kHz to 192kHz	RTP Payload Format for Vorbis Vorbis Vorbis is a free software / open source project headed by the Xiph.Org Foundation . The project produces an audio format specification and software implementation for lossy audio compression...  Encoded Audio	RFC 5215
dynamic (or profile)	speex	audio	1	8000, 16000 or 32000	RTP Payload Format for the Speex Speex Speex is a patent-free audio compression format designed for speech and also a free software speech codec that may be used on VoIP applications and podcasts. It is based on the CELP speech coding algorithm. Speex claims to be free of any patent restrictions and is licensed under the revised BSD...  Codec	RFC 5574
dynamic (96-127)	mpa-robust	audio		90000	A More Loss-Tolerant RTP Payload Format for MP3 MP3 MPEG-1 or MPEG-2 Audio Layer III, more commonly referred to as MP3, is a patented digital audio encoding format using a form of lossy data compression...  Audio	RFC 5219
dynamic (or profile)	MP4A-LATM	audio		90000 or others	RTP Payload Format for MPEG-4 Audio	RFC 3016
dynamic (or profile)	MP4V-ES	video		90000 or others	RTP Payload Format for MPEG-4 Visual	RFC 3016
dynamic (or profile)	mpeg4-generic	audio/video		90000 or other	RTP Payload Format for Transport of MPEG-4 MPEG-4 MPEG-4 is a method of defining compression of audio and visual digital data. It was introduced in late 1998 and designated a standard for a group of audio and video coding formats and related technology agreed upon by the ISO/IEC Moving Picture Experts Group under the formal standard ISO/IEC...  Elementary Streams	RFC 3640
dynamic	L8	audio	(various)	(various)	Linear PCM 8-bit audio with 128 offset	RFC 3551 Section 4.5.10 and Table 5
dynamic	DAT12	audio	(various)	8000, 11025, 16000, 22050, 24000, 32000, 44100, 48000 or others	IEC 61119 12-bit nonlinear audio	RFC 3190 Section 3
dynamic	L16	audio	(various)	8000, 11025, 16000, 22050, 24000, 32000, 44100, 48000 or others	Linear PCM 16-bit audio	RFC 3551 Section 4.5.11, RFC 2586
dynamic	L20	audio	(various)	8000, 11025, 16000, 22050, 24000, 32000, 44100, 48000 or others	Linear PCM 20-bit audio	RFC 3190 Section 4
dynamic	L24	audio	(various)	8000, 11025, 16000, 22050, 24000, 32000, 44100, 48000 or others	Linear PCM 24-bit audio	RFC 3190 Section 4

RFC 3551 lists details of the codec

Codec

A codec is a device or computer program capable of encoding or decoding a digital data stream or signal. The word codec is a portmanteau of "compressor-decompressor" or, more commonly, "coder-decoder"...

, or a reference for the details is provided. Payload identifiers 96–127 are reserved for payloads 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.

External links

• IANA assignments of Real-Time Transport Protocol (RTP) Parameters