RTCTrackEvent

{{APIRef("WebRTC")}} 

The WebRTC API interface RTCTrackEvent represents the {{domxref("RTCPeerConnection.track_event", "track")}}  event, which is sent when a new {{domxref("MediaStreamTrack")}}  is added to an {{domxref("RTCRtpReceiver")}}  which is part of the {{domxref("RTCPeerConnection")}} .

The target is the RTCPeerConnection object to which the track is being added.

This event is sent by the WebRTC layer to the website or application, so you will not typically need to instantiate an RTCTrackEvent yourself.

{{InheritanceDiagram}} 

Constructor

• {{domxref("RTCTrackEvent.RTCTrackEvent", "RTCTrackEvent()")}} 
  • : Creates and returns a new RTCTrackEvent object. You will probably not need to create new track events yourself, since they’re typically created by the WebRTC infrastructure and sent to the connection’s {{domxref("RTCPeerConnection.track_event", "ontrack")}}  event handler.

Instance properties

Since RTCTrackEvent is based on {{domxref("Event")}} , its properties are also available.

• {{domxref("RTCTrackEvent.receiver", "receiver")}}  {{ReadOnlyInline}} 
  • : The {{domxref("RTCRtpReceiver")}}  used by the track that’s been added to the RTCPeerConnection.
• {{domxref("RTCTrackEvent.streams", "streams")}}  {{ReadOnlyInline}}  {{optional_inline}} 
  • : An array of {{domxref("MediaStream")}}  objects, each representing one of the media streams to which the added {{domxref("RTCTrackEvent.track", "track")}}  belongs. By default, the array is empty, indicating a streamless track.
• {{domxref("RTCTrackEvent.track", "track")}}  {{ReadOnlyInline}} 
  • : The {{domxref("MediaStreamTrack")}}  which has been added to the connection.
• {{domxref("RTCTrackEvent.transceiver", "transceiver")}}  {{ReadOnlyInline}} 
  • : The {{domxref("RTCRtpTransceiver")}}  being used by the new track.

Track event types

There is only one type of track event.

track

The {{domxref("RTCPeerConnection.track_event", "track")}}  event is sent to the {{domxref("RTCPeerConnection")}}  when a new track has been added to the connection. By the time the track event is delivered to the RTCPeerConnection’s {{domxref("RTCPeerConnection.track_event", "ontrack")}}  handler, the new media has completed its negotiation for a specific {{domxref("RTCRtpReceiver")}}  (which is specified by the event’s {{domxref("RTCTrackEvent.receiver", "receiver")}}  property).

In addition, the {{domxref("MediaStreamTrack")}}  specified by the receiver’s {{domxref("RTCRtpReceiver.track", "track")}}  is the same one specified by the event’s {{domxref("RTCTrackEvent.track", "track")}} , and the track has been added to any associated remote {{domxref("MediaStream")}}  objects.

You can add a track event listener to be notified when the new track is available so that you can, for example, attach its media to a {{HTMLElement("video")}}  element, using either {{domxref("EventTarget.addEventListener", "RTCPeerConnection.addEventListener()")}}  or the ontrack event handler property.

[!NOTE] It may be helpful to keep in mind that you receive the track event when a new inbound track has been added to your connection, and you call {{domxref("RTCPeerConnection.addTrack", "addTrack()")}}  to add a track to the far end of the connection, thereby triggering a track event on the remote peer.

Example

This simple example creates an event listener for the {{domxref("RTCPeerConnection.track_event", "track")}}  event which sets the {{domxref("HTMLMediaElement.srcObject", "srcObject")}}  of the {{HTMLElement("video")}}  element with the ID video-box to the first stream in the list passed in the event’s {{domxref("RTCTrackEvent.streams", "streams")}}  array.

peerConnection.addEventListener(
  "track",
  (e) => {
    let videoElement = document.getElementById("video-box");
    videoElement.srcObject = e.streams[0];
  },
  false,
);

Specifications

{{Specifications}} 

Browser compatibility

{{Compat}}