negotiationneeded

Negotiationneeded is an event in the WebRTC API that is fired on an RTCPeerConnection to indicate that renegotiation of the session description is required. It signals that pending changes to the connection, such as modifications to tracks or transceivers, require updating the local or remote session descriptions.

When this event is emitted, the application typically starts a signaling round to renegotiate the connection. The common flow is to create an offer, set the local description, and transmit the offer to the remote peer. The remote peer then sets the received offer as its remote description, creates an answer, sets its local description, and sends the answer back. The initiating side completes the process by setting the remote description with the received answer. This pattern allows both peers to agree on the updated media configuration.

Negotiationneeded is often triggered by changes that affect the signaling state, such as adding or removing tracks via addTrack, replacing a track with replaceTrack, or other changes that require updating the session description. Implementations normally fire this event only after such changes, and not for the initial offer/answer exchange that occurs at connection setup, which is usually initiated manually by the application.

To avoid negotiation conflicts and loops (glare), developers typically serialize negotiations with a guard flag or a queue, ensuring only one negotiation is in progress at a time. Some applications also debounce or coalesce multiple changes before starting renegotiation.

See also: WebRTC, RTCPeerConnection, signaling, offer/answer model.