groupId property is a
describing the requested or mandatory constraints placed upon the value of the
groupId constrainable property.
If needed, you can determine whether or not this constraint is supported by checking
the value of
MediaTrackSupportedConstraints.groupId as returned by a call
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) group IDs which are acceptable as the source of media
Group IDs are unique for a given origin for the duration of a single browsing session, and are shared by all media sources that come from the same physical device. For example, the microphone and speaker on the same headset would share a group ID. This makes it possible to use the group ID to ensure that the audio and input devices are on the same headset by retrieving the group ID of the input device and specifying it when asking for an output device, perhaps.
However, the value of the
groupId is 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
groupId when you call
getCapabilities(), and keep in mind
that this value will change for each browsing session.
Because of this, there's no use for the group ID when calling
MediaStreamTrack.applyConstraints(), since there is only one possible
value, and you can't use it to ensure the same group is used across multiple browsing
sessions when calling
See the Constraint exerciser example.
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