rtcloopbackhack.js

let rtcConnection = null;
let rtcLoopbackConnection = null;
let loopbackStream = new MediaStream(); // this is the stream you will read from for actual audio output

const offerOptions = {
  offerVideo: true,
  offerAudio: true,
  offerToReceiveAudio: false,
  offerToReceiveVideo: false,
};

let offer, answer;

// initialize the RTC connections

this.rtcConnection = new RTCPeerConnection();
this.rtcLoopbackConnection = new RTCPeerConnection();

this.rtcConnection.onicecandidate = e =>
  e.candidate && this.rtcLoopbackConnection.addIceCandidate(new RTCIceCandidate(e.candidate));
this.rtcLoopbackConnection.onicecandidate = e =>
  e.candidate && this.rtcConnection.addIceCandidate(new RTCIceCandidate(e.candidate));

this.rtcLoopbackConnection.ontrack = e =>
  e.streams[0].getTracks().forEach(track => this.loopbackStream.addTrack(track));


// setup the loopback
this.rtcConnection.addStream(stream); // this stream would be the processed stream coming out of Web Audio API destination node

offer = await this.rtcConnection.createOffer(offerOptions);
await this.rtcConnection.setLocalDescription(offer);

await this.rtcLoopbackConnection.setRemoteDescription(offer);
answer = await this.rtcLoopbackConnection.createAnswer();
await this.rtcLoopbackConnection.setLocalDescription(answer);

await this.rtcConnection.setRemoteDescription(answer);

@berkon Unfortunately it does not work this way. All this does is re-add echo cancellation to a stream which has been passed through WebAudio and thus lost it's echo cancellation (but all the input data to apply cancellation still exists). Chromium does not consider screen capture audio for echo cancellation so this wont work. Echo cancellation works based on running the algorithm on an input audio stream and output audio stream. In this case there is no "input" to be considered as Chromium totally bypasses it for screenshare, and thus no echo cancelation from that source can be applied to the output stream. It looks like there are patches to workaround this in the issue you linked to though.

@alexciarlillo can you give me some demo which can run as webpage?

@liyoubdu sorry I do not have time to do this right now (I am just returning to work after paternity leave and have much to catch up on). But if you do come up with a single page working example please do share it back here for others to reference.