SDP

SDP (Session Description Protocol) is a standard for describing multimedia sessions. It contains information such as media types, transport addresses, timing, and codecs.

Here is a typical SDP message:

v=0
o=alice 2890844526 2890844526 IN IP4 host.anywhere.com
s=
c=IN IP4 host.anywhere.com
t=0 0
m=audio 49170 RTP/AVP 0
a=rtpmap:0 PCMU/8000
m=video 51372 RTP/AVP 31
a=rtpmap:31 H261/90000
m=video 53000 RTP/AVP 32
a=rtpmap:32 MPV/90000

SDP is used together with protocols such as RTP and RTSP. During WebRTC session negotiation, one peer sends an offer describing the connection it wants, and the other replies with an answer describing what it accepts. Both are session descriptions in SDP format, exchanged over a signaling channel and applied with RTCPeerConnection.setLocalDescription() and RTCPeerConnection.setRemoteDescription().