The RTCIceServer dictionary defines how to connect to a single ICE server (such as a STUN or TURN server). It includes both the URL and the necessary credentials, if any, to connect to the server.
The VRLayer interface (dictionary) of the WebVR API represents a content layer (an HTMLCanvasElement or OffscreenCanvas) that you want to present in a VR HMD.
The MediaTrackConstraints dictionary is used to describe a set of capabilities and the value or values each can take on. A constraints dictionary is passed into applyConstraints() to allow a script to establish a set of ideal values and/or preferred ranges of values for the track, and the most recently-requested set of custom constraints can be retrieved by calling getConstraints().
The MediaTrackSupportedConstraints dictionary establishes the list of constrainable properties recognized by the user agent or browser in its implementation of the MediaStreamTrack object. An object conforming to MediaTrackSupportedConstraints is returned by MediaDevices.getSupportedConstraints().
The MediaTrackSettings dictionary is used to return the current values configured for each of a MediaStreamTrack's settings. These values will adhere as closely as possible to any constraints previously set using applyConstraints(), and will adhere to the default constraints for any properties whose constraints haven't been changed, or whose customized constraints couldn't be matched.