MediaStreamAudioDestinationNode - Web APIs
the mediastreamaudiodestinationnode interface represents an audio destination consisting of a webrtc mediastream with a single audiomediastreamtrack, which can be used in a similar way to a mediastream obtained from navigator.getusermedia.
... mediastreamaudiodestinationnode.stream is a mediastream containing a single audiomediastreamtrack with the same number of channels as the node itself.

MediaStreamAudioDestinationNode.stream - Web APIs
the stream property of the audiocontext interface represents a mediastream containing a single audiomediastreamtrack with the same number of channels as the node itself.

Web Audio API - Web APIs
mediastreamaudiodestinationnode the mediastreamaudiodestinationnode interface represents an audio destination consisting of a webrtc mediastream with a single audiomediastreamtrack, which can be used in a similar way to a mediastream obtained from getusermedia().