RTCPeerConnection.ontrack

The RTCPeerConnection property ontrack is an EventHandler which specifies a function to be called when the track event occurs, indicating that a track has been added to the RTCPeerConnection. The function receives as input the event object, of type RTCTrackEvent; this event is sent when a new incoming MediaStreamTrack has been created and associated with an RTCRtpReceiver object which has been added to the set of receivers on connection.

Syntax

RTCPeerConnection.ontrack = eventHandler;

Value

Set ontrack to be a function you provide that accepts as input a RTCTrackEvent object describing the new track and how it's being used. This information includes the MediaStreamTrack object representing the new track, the RTCRtpReceiver and RTCRtpTransceiver, and a list of MediaStream objects which indicates which stream or streams the track is part of..

Example

This example, taken from the code for the article Signaling and video calling, connects the incoming track to the <video> element which will be used to display the incoming video.

pc.ontrack = function(event) {
  document.getElementById("received_video").srcObject = event.streams[0];
  document.getElementById("hangup-button").disabled = false;
};

The first line of our ontrack event handler takes the first stream in the incoming track and sets the srcobject attribute to that. This connects that stream of video to the element so that it begins to be presented to the user. The second line of code simply enables a "hang up" button, which the user can use to disconnect from the call.

Specifications

Specification Status Comment
WebRTC 1.0: Real-time Communication Between Browsers
The definition of 'RTCPeerConnection.ontrack' in that specification.
Candidate Recommendation Initial specification.

Browser compatibility

DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
ontrackChrome Full support 64Edge Full support ≤18Firefox Full support 22IE No support NoOpera Full support 43
Notes
Full support 43
Notes
Notes Promise-based version.
No support 37 — 43
Safari Full support 11WebView Android Full support 64Chrome Android Full support 64Firefox Android Full support 44Opera Android Full support 43
Notes
Full support 43
Notes
Notes Promise-based version.
No support 37 — 43
Safari iOS Full support YesSamsung Internet Android Full support 6.0

Legend

Full support
Full support
No support
No support
See implementation notes.
See implementation notes.

See also