MediaTrackSettings.groupId - Web APIs 编辑

The MediaTrackSettings dictionary's groupId property is a browsing-session unique DOMString which identifies the group of devices which includes the source for the MediaStreamTrack. This lets you determine what value was selected to comply with your specified constraints for this property's value as described in the MediaTrackConstraints.groupId 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.groupId as returned by a call to MediaDevices.getSupportedConstraints(). However, typically this is unnecessary since browsers will ignore any constraints they're unfamiliar with.

Because RTP doesn't include this information, tracks associated with a WebRTC RTCPeerConnection will never include this property.

Syntax

var groupId = MediaTrackSettings.groupId;

Value

A DOMString whose value is a browsing-session unique identifier for a group of devices which includes the source of the track's contents. Two devices share the same group ID if they belong to the same physical hardware device. For example, a headset has two devices on it: a microphone which can serve as a source for audio tracks and a speaker which can serve as an output for audio.

The group ID is not usable across multiple browsing sessions. However, it can be used to ensure that audio input and output are both being performed on the same headset, for example, or to ensure that the built-in camera and microphone on a phone are being used for video conferencing purposes.

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 this property isn't stable across browsing sessions, its usefulness when calling getUserMedia() is generally limited to ensuring that tasks performed during the same browsing session use devices from the same group (or that they don't use devices from the same group). There is no situation in which the groupId is useful when calling applyConstraints(), since the value can't be changed.

Example

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

Specifications

Browser compatibility

BCD tables only load in the browser

See also

• Media Capture and Streams API
• Capabilities, constraints, and settings
• MediaTrackSettings.deviceId
• MediaTrackConstraints.groupId
• MediaTrackSettings