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8.2.1. Mapping of Payload Type Parameters to SDP

8.2.1. Mapping of Payload Type Parameters to SDP​

The media type video/H264 string is mapped to fields in the Session Description Protocol (SDP) [6] as follows:

  • The media name in the "m=" line of SDP MUST be video.

  • The encoding name in the "a=rtpmap" line of SDP MUST be H264 (the media subtype).

  • The clock rate in the "a=rtpmap" line MUST be 90000.

  • The OPTIONAL parameters profile-level-id, max-recv-level, max- mbps, max-smbps, max-fs, max-cpb, max-dpb, max-br, redundant-pic- cap, use-level-src-parameter-sets, in-band-parameter-sets, level- asymmetry-allowed, packetization-mode, sprop-interleaving-depth, sprop-deint-buf-req, deint-buf-cap, sprop-init-buf-time, sprop- max-don-diff, max-rcmd-nalu-size, sar-understood, and sar- supported, when present, MUST be included in the "a=fmtp" line of SDP. These parameters are expressed as a media type string, in the form of a semicolon-separated list of parameter=value pairs.

  • The OPTIONAL parameters sprop-parameter-sets and sprop-level- parameter-sets, when present, MUST be included in the "a=fmtp" line of SDP or conveyed using the "fmtp" source attribute as specified in Section 6.3 of [9]. For a particular media format (i.e., RTP payload type), a sprop-parameter-sets or sprop-level- parameter-sets MUST NOT be both included in the "a=fmtp" line of

SDP and conveyed using the "fmtp" source attribute. When included in the "a=fmtp" line of SDP, these parameters are expressed as a media type string, in the form of a semicolon-separated list of parameter=value pairs. When conveyed using the "fmtp" source attribute, these parameters are only associated with the given source and payload type as parts of the "fmtp" source attribute.

Informative note: Conveyance of sprop-parameter-sets and sprop- level-parameter-sets using the "fmtp" source attribute allows for out-of-band transport of parameter sets in topologies like Topo-Video-switch-MCU [29].

An example of media representation in SDP is as follows (Baseline profile, Level 3.0, some of the constraints of the Main profile may not be obeyed):

m=video 49170 RTP/AVP 98
a=rtpmap:98 H264/90000
a=fmtp:98 profile-level-id=42A01E; packetization-mode=1; sprop-parameter-sets=<parameter sets data>
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