The MediaTrackSettings dictionary's deviceId property is a DOMString which uniquely identifies the source for the corresponding MediaStreamTrack for the origin corresponding to the browsing session. This lets you determine what value was selected to comply with your specified constraints for this property's value as described in the MediaTrackConstraints.deviceId property you provided when calling either getUserMedia().

If needed, you can determine whether or not this constraint is supported by checking the value of MediaTrackSupportedConstraints.deviceId as returned by a call to MediaDevices.getSupportedConstraints(). However, typically this is unnecessary since browsers will simply ignore any constraints they're unfamiliar with.


var deviceId = MediaTrackSettings.deviceId;


A DOMString whose value is an origin-unique identifier for the track's source. This ID is valid across multiple browsing sessions for the same origin and is guaranteed to be different for all other origins, so you can safely use it to request the same source be used for multiple sessions, for example.

The actual value of the string, however, is determined by the source of the track, and there is no guarantee what form it will take, although the specification does recommend it be a GUID.

Since there is a one-to-one pairing of ID with each source, all tracks with the same source will share the same ID for any given origin, so MediaStreamTrack.getCapabilities() will always return exactly one value for deviceId. That makes the device ID not useful for any changes to constraints when calling MediaStreamTrack.applyConstraints().

An exception to the rule that device IDs are the same across browsing sessions: private browsing mode will use a different ID, and will change it each browsing session.


See "Example: Constraint exerciser" in Capabilities, constraints, and settings for an example.


Specification Status Comment
Media Capture and Streams
The definition of 'deviceId' in that specification.
Editor's Draft Initial specification.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Basic support (Yes) 36 (36) No support (Yes) ?
Feature Android Android Webview Firefox Mobile (Gecko) IE Mobile Opera Mobile Safari Mobile Chrome for Android
Basic support ? (Yes) 36.0 (36) No support ? ? (Yes)

See also

Document Tags and Contributors

 Contributors to this page: Sheppy
 Last updated by: Sheppy,