MediaStreamAudioDestinationNode.stream

The stream property of the AudioContext interface represents a MediaStream containing a single AudioMediaStreamTrack with the same number of channels as the node itself.

You can use this property to get a stream out of the audio graph and feed it into another construct, such as a Media Recorder.

Syntax

var audioCtx = new AudioContext();
var destination = audioCtx.createMediaStreamDestination();
var myStream = destination.stream;

Value

A MediaStream.

Example

In the following simple example, we create a MediaStreamAudioDestinationNode, an OscillatorNode and a MediaRecorder (the example will therefore only work in Firefox at this time.) The MediaRecorder is set up to record information from the MediaStreamDestinationNode.

When the button is clicked, the oscillator starts, and the MediaRecorder is started. When the button is stopped, the oscillator and MediaRecorder both stop, and the MediaRecorder requests data. This causes the dataavailable event to fire, and the event data is pushed into the chunks array. After that, the stop event fires, a new blob is made of type opus — which contains the data in the chunks array, and a new window (tab) is then opened that points to a URL created from the blob.

From here, you can play and save the opus file.

<!DOCTYPE html>
<html>
  <head>
    <title>createMediaStreamDestination() demo</title>
  </head>
  <body>
    <h1>createMediaStreamDestination() demo</h1>

    <p>Encoding a pure sine wave to an Opus file </p>
    <button>Make sine wave</button>
    <script>
     var b = document.querySelector("button");
     var clicked = false;
     var chunks = [];
     var ac = new AudioContext();
     var osc = ac.createOscillator();
     var dest = ac.createMediaStreamDestination();
     var mediaRecorder = new MediaRecorder(dest.stream);
     osc.connect(dest);

     b.addEventListener("click", function(e) {
       if (!clicked) {
           mediaRecorder.start();
           osc.start(0);
           e.target.innerHTML = "Stop recording";
           clicked = true;
         } else {
           mediaRecorder.stop();
           mediaRecorder.requestData();
           osc.stop(0);
           e.target.disabled = true;
         }
     });

     mediaRecorder.ondataavailable = function(evt) {
       // push each chunk (blobs) in an array
       chunks.push(evt.data);
     };

     mediaRecorder.onstop = function(evt) {
       // Make blob out of our blobs, and open it.
       var blob = new Blob(chunks, { 'type' : 'audio/ogg; codecs=opus' });
       window.location.href = URL.createObjectURL(blob);
     };
    </script>
  </body>
</html>

Note: You can view this example live, or study the source code, on Github.

Specifications

Specification	Status	Comment
Web Audio API The definition of 'stream' in that specification.	Working Draft

Feature	Chrome	Firefox (Gecko)	Internet Explorer	Opera	Safari (WebKit)
Basic support	10.0webkit	25.0 (25.0)	Not supported	15.0webkit 22 (unprefixed)	6.0webkit

Feature	Android	Firefox Mobile (Gecko)	Firefox OS	IE Mobile	Opera Mobile	Safari Mobile	Chrome for Android
Basic support	?	26.0	1.2	?	?	?	33.0