WebRTC SDP Analyzer

SDP (Session Description Protocol) is a text-based format used to negotiate media capabilities between WebRTC peers. An offer SDP describes what the caller supports (codecs, ICE candidates, DTLS fingerprint), and an answer SDP is the callee's response. Together they form the basis of the WebRTC handshake.

ICE (Interactive Connectivity Establishment) candidates are potential network paths between peers. 'host' candidates are local network addresses, 'srflx' (server-reflexive) candidates come from a STUN server and reflect your public IP, and 'relay' candidates come from a TURN server and handle cases where direct or STUN-based connections fail. More candidate types = better chances of a successful connection.

The DTLS fingerprint (usually SHA-256) is a hash of the peer's TLS certificate. It's included in the SDP so both peers can verify each other's identity during the DTLS handshake, preventing man-in-the-middle attacks. It changes with each session as WebRTC generates self-signed certificates.

SSRC (Synchronization Source identifier) is a 32-bit number that uniquely identifies each media stream within an RTP session. In WebRTC, each audio or video track gets its own SSRC. When simulcast is used (multiple resolutions), you'll see multiple SSRCs per track — often grouped with SSRC-GROUP:FID for RTX (retransmission) pairing.

'sendrecv' means the peer can both send and receive media on this track. 'sendonly' means it will only send. 'recvonly' means it will only receive. 'inactive' means the track exists but no media flows. These directions are negotiated between the offer and answer.

Trickle ICE is a WebRTC optimization where ICE candidates are sent incrementally as they're discovered, rather than waiting for all candidates before sending the SDP. If you see 'a=ice-options:trickle' in the SDP and few or no candidates, the candidates arrive separately via signaling. This reduces connection setup time significantly.