How to get a media stream of the speaker's output to transfer it over the network or record it?

I'm trying to get the output of the speaker and then do what ever I want with this stream .

I tried to use this to get the speaker's stream:

var mySpeakerStream = new MediaStream();
navigator.mediaDevices.getUserMedia({audio: {deviceId : {exact: mySpeakerId} } }).then(s => {        
        myStream.addTrack(s.getAudioTracks()[0]);
}).catch( console.log('failed') );

I expected to get the speaker but I did not , then I realised that the getUserMedia method returns a MediaStream of an input device only. Is there any way to get a stream of the speaker's output?

after more thinking about the issue I found that: I can use getDisplyMedia method but it doesn't support audio only requests, so I tried to get the stream of both audio and video then I get the audio tracks out of it just like this:

var speaker = new MediaStream;
if (navigator.getDisplayMedia) {
    navigator.getDisplayMedia({
        video: true ,
        audio: true
    }).then(stream => {
        speaker.addTrack(stream.getAudioTracks()[0].clone());
        // stopping and removing the video track to enhance the performance
        stream.getVideoTracks()[0].stop();
        stream.removeTrack(stream.getVideoTracks()[0]);
    }).catch(() => {
        console.error('failed')
    });
} else if (navigator.mediaDevices.getDisplayMedia) {
    navigator.mediaDevices.getDisplayMedia({
        video: true ,
        audio: true
    }).then(stream => {
        speaker.addTrack(stream.getAudioTracks()[0].clone());
        // stopping and removing the video track to enhance the performance
        stream.getVideoTracks()[0].stop();
        stream.removeTrack(stream.getVideoTracks()[0]);
    }).catch(() => {
        console.error('failed')
    });
}

I know that does not solve the issue perfectly but I think it's useful .

'still working and waiting for more solutions'