deviceId property is a string which
uniquely identifies the source for the corresponding
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
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.
A string 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
deviceId. That makes the device ID not useful for any changes to
constraints when calling
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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