chrome.desktopCapture-无法同时录制系统音频和麦克风?

我已经建立了一个Chrome扩展,可以捕捉屏幕活动和麦克风输入,并输出一个视频文件。自从 chrome.desktopCapture 无法录制音频 除了屏幕截图,我还将把麦克风放在独立的流中。所以:

//get screen stream
chrome.desktopCapture.chooseDesktopMedia(['screen'], null, (stream_id, opts) => {
    let constraints = {video: mandatory: {
        chromeMediaSource: 'desktop',
        chromeMediaSourceId: stream_id
    }};
    navigator.mediaDevices.getUserMedia(constraints).then((stream) => {
        video_stream = stream;
    });
});

//get mic stream
navigator.mediaDevices.getUserMedia({audio: true}).then((stream) => {
    audio_stream = stream;
});

let master_stream = new MediaStream(video_stream);
master_stream.addTrack(audio_stream.getTracks()[0]);

最后,当我最终得到一个视频文件时,这个效果很好。我有屏幕和麦克风。

问:如果我要求Chrome也录制系统声音,为什么这项技术不起作用?

['screen'] 到 ['screen', 'audio'] ,其他一切都一样,我最终在结果视频中没有麦克风。

getTracks() 在 master_stream ,我得到的是:

Array(3)
    0: MediaStreamTrack {kind: "audio", id: "9ee3ee33-73ee-41e4-957c-d6fd3aaada43", label: "System Audio", enabled: true, muted: false, …}
    1: MediaStreamTrack {kind: "audio", id: "ab2429a1-7f75-48f2-9ee1-6a4bfd7ca942", label: "Default - Microphone (Samson Meteor Mic) (17a0:0310)", enabled: true, muted: false, …}
    2: MediaStreamTrack {kind: "video", id: "4ecb1929-31d0-4a79-8cbc-1a8759323c3b", label: "screen:0:0", enabled: true, muted: false, …}