Muaz Khan edited this page May 6, 2018 · 2 revisions

This wiki explains how to extract audio-only stream from Audio/Video MediaStream object using Firefox.

// mozAV2AudioOnly.js
// this script takes MediaStream with both audio/video tracks
// and returns only audio stream
// keep "audioContext" global to make sure "destination" isn't auto disconnected.
var audioContext, microphone, audioDestination;

    audio: true,
    video: true
}).then(function(avStream) {
    audioContext = new AudioContext();

    // simply connect with audio (live) APM source
    microphone = audioContext.createMediaStreamSource(avStream);

    // simply create destination node
    audioDestination = audioContext.createMediaStreamDestination();

    // preview in DOM
    var audio = document.createElement('audio');
    audio.src = URL.createObjectURL(;
    audio.controls = true;;
}).catch(function(error) {});

Construct New MediaStream

var audioOnlyStream = new MediaStream();

cameraStream.getAudioTracks().forEach(function(audioTrack) {

var recorder = new MediaRecorder(audioOnlyStream);

removeTrack (video track)

cameraStream.getVideoTracks().forEach(function(videoTrack) {

// now cameraStream has no video tracks
// it has only audio tracks
var recorder = new MediaRecorder(cameraStream);
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