Capture system sound from browser - google-chrome

Question

I am trying to build a web app that captures both local and remote audios from a webrtc call, but I can`t record the remote audio(using recordRTC).
I was wondering if I could capture the system sound somehow.
Is there a way to capture the system sound (not just the mic) from the browser. Maybe an extension?

Answer 1

In Chrome, the chrome.desktopCapture extension API can be used to capture the screen, which includes system audio (but only on Windows and Chrome OS and without plans for OS X or Linux). E.g.
chrome.desktopCapture.chooseDesktopMedia([
'screen', 'window' // ('tab' is not supported; use chrome.tabCapture instead)
], function(streamId) {
navigator.webkitGetUserMedia({
audio: {
mandatory: {
chromeMediaSource: 'system',
chromeMediaSourceId: streamId
}
},
video: false, // We only want audio for now.
}, function(stream) {
// Do what you want with this MediaStream.
}, function(error) {
// Handle error
});
});
I'm not sure whether Firefox can capture system sound, but at the very least it is capable of capturing some output (tab/window/browser/OS?).
First you need to visit about:config and set media.getusermedia.audiocapture.enabled to true (this could be automated through a Firefox add-on). Then the stream can be captured as follows:
navigator.mozGetUserMedia({
audio: {
mediaSource: 'audioCapture'
},
video: false, // Just being explicit, we only want audio for now
}, function(stream) {
// Do what you want with this MediaStream.
}, function(error) {
// Handle error
});
This was implemented in Firefox 42, at https://bugzilla.mozilla.org/show_bug.cgi?id=1156472

Answer 2

This is possible with the new Screen Capture API, but browser support is still limited.
See the "Browser compatibility" section in the above-linked MDN page for details. Some browsers currently don't yet support audio capture, and some others currently only allow audio capture from a specific tab, rather than the operating system as a whole.
Example code:
videoElem.srcObject = await navigator.mediaDevices.getDisplayMedia({audio:true, video:true});