XMediaLib.SDP.Media (xmedialib v0.3.0)

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One SDP media section (m= line) and its media-level attributes.

What problem this solves

A WebRTC offer contains one or more m= sections (audio, video, application). Each section lists ports, transports, payload types, and dozens of a= attributes for ICE, codecs, and SSRC metadata. This struct holds one parsed media block so SFU and gateway code can read or patch a single stream without reparsing the whole session.

Each m= block describes a single media stream: type (audio, video, application), port, transport protocol, and format list. Following a= lines carry ICE credentials, DTLS fingerprints, codec mappings, SSRC metadata, and WebRTC-specific extensions. The parser promotes well-known attributes into typed fields; anything else remains in :attributes.

RFCs

Summary

Types

attribute()

Unpromoted media-level attribute as {name, value} or {name, true}.

direction()

Media direction from a=sendrecv, a=sendonly, a=recvonly, or a=inactive.

protocol()

Transport protocol from the m= line.

t()

Media description fields for one m= section.

type()

Media kind from the m= line; known atoms or the raw string.

Types

attribute()

@type attribute() :: {String.t(), String.t() | true}

Unpromoted media-level attribute as {name, value} or {name, true}.

direction()

@type direction() :: :sendrecv | :sendonly | :recvonly | :inactive

Media direction from a=sendrecv, a=sendonly, a=recvonly, or a=inactive.

protocol()

@type protocol() :: :UDP_TLS_RTP_SAVPF | :RTP_SAVPF | :UDP_DTLS_SCTP | String.t()

Transport protocol from the m= line.

Known WebRTC values include :UDP_TLS_RTP_SAVPF (DTLS-SRTP), :RTP_SAVPF, and :UDP_DTLS_SCTP (data channels). Other strings pass through unchanged.

t()

@type t() :: %XMediaLib.SDP.Media{
  attributes: [attribute()],
  candidates: [XMediaLib.SDP.Candidate.t()],
  codecs: [XMediaLib.SDP.Codec.t()],
  connection: XMediaLib.SDP.Connection.t() | nil,
  dcmap: [XMediaLib.SDP.Dcmap.t()],
  direction: direction() | nil,
  extmaps: [XMediaLib.SDP.Extmap.t()],
  fingerprint: XMediaLib.SDP.Fingerprint.t() | nil,
  fmtp: [XMediaLib.SDP.Fmtp.t()],
  formats: [String.t()],
  ice_pwd: String.t() | nil,
  ice_ufrag: String.t() | nil,
  max_message_size: non_neg_integer() | nil,
  mid: String.t() | nil,
  port: non_neg_integer() | nil,
  protocol: protocol() | nil,
  rtcp_fb: [XMediaLib.SDP.RtcpFb.t()],
  rtcp_mux: boolean(),
  sctp_port: non_neg_integer() | nil,
  setup: :active | :passive | :actpass | nil,
  ssrcs: [XMediaLib.SDP.Ssrc.t()],
  type: type() | nil
}

Media description fields for one m= section.

Fields

  • :type - media kind (:audio, :video, :application, or string)
  • :port - port number from the m= line (0 means rejected/hold)
  • :protocol - transport, e.g. :UDP_TLS_RTP_SAVPF
  • :formats - payload type or format tokens from the m= line
  • :connection - optional media-level c= override
  • :ice_ufrag - ICE username fragment (a=ice-ufrag)
  • :ice_pwd - ICE password (a=ice-pwd)
  • :candidates - parsed a=candidate lines
  • :fingerprint - DTLS certificate fingerprint (a=fingerprint)
  • :setup - DTLS role hint (a=setup: :active, :passive, or :actpass)
  • :mid - media identification tag for BUNDLE (a=mid)
  • :direction - send/receive direction attribute
  • :rtcp_mux - true when a=rtcp-mux is present
  • :codecs - dynamic payload mappings from a=rtpmap
  • :fmtp - format parameters from a=fmtp
  • :rtcp_fb - RTCP feedback tokens from a=rtcp-fb
  • :extmaps - RTP header extension maps from a=extmap
  • :ssrcs - SSRC attributes from a=ssrc
  • :sctp_port - SCTP port for data channels (a=sctp-port)
  • :max_message_size - SCTP max message size (a=max-message-size)
  • :dcmap - data channel maps from a=dcmap
  • :attributes - other media-level a= lines

type()

@type type() :: :audio | :video | :application | String.t()

Media kind from the m= line; known atoms or the raw string.