If needed, you can determine whether or not this constraint is supported by checking
the value of
MediaTrackSupportedConstraints.deviceId as returned by a
MediaDevices.getSupportedConstraints(). However, typically this
is unnecessary since browsers will ignore any constraints they're unfamiliar with.
An object based on
ConstrainDOMString specifying one or more acceptable,
ideal, and/or exact (mandatory) device IDs which are acceptable as the source of media
Device IDs are unique for a given origin, and are guaranteed to be the same across
browsing sessions on the same origin. However, the value of the
determined by the source of the track's content, and there's no particular format
mandated by the specification (although some kind of GUID is recommended). That means
that a given track will only return one value for the
deviceId when you
Because of this, there's no use for the device ID when calling
MediaStreamTrack.applyConstraints(), since there is only one possible
value; however, you can record a
deviceId and use it to ensure that you get
the same source for multiple calls to
Note: 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 the Constraint exerciser example.
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