WebRTC mix local and remote audio steams and record - webrtc

Question

So far i've found a way only to record either local or remote using MediaRecorder API but is it possible to mix and record both steams and get a blob?
Please note its audio steam only and i don't want to mix/record in server side.
I've a RTCPeerConnection as pc.
var local_stream = pc.getLocalStreams()[0];
var remote_stream = pc.getRemoteStreams()[0];
var audioChunks = [];
var rec = new MediaRecorder(local_stream);
rec.ondataavailable = e => {
audioChunks.push(e.data);
if (rec.state == "inactive")
// Play audio using new blob
}
rec.start();
Even i tried adding multiple tracks in MediaStream API but it still gives only first track audio. Any help or insight 'd be appreciated!

Answer 1

The WebAudio API can do mixing for you. Consider this code if you want to record all the audio tracks in the array audioTracks:
const ac = new AudioContext();
// WebAudio MediaStream sources only use the first track.
const sources = audioTracks.map(t => ac.createMediaStreamSource(new MediaStream([t])));
// The destination will output one track of mixed audio.
const dest = ac.createMediaStreamDestination();
// Mixing
sources.forEach(s => s.connect(dest));
// Record 10s of mixed audio as an example
const recorder = new MediaRecorder(dest.stream);
recorder.start();
recorder.ondataavailable = e => console.log("Got data", e.data);
recorder.onstop = () => console.log("stopped");
setTimeout(() => recorder.stop(), 10000);