MediaRecorder.ondataavailable

The MediaRecorder.ondataavailable event handler (part of the MediaStream Recording API) handles the dataavailable event, letting you run code in response to Blob data being made available for use.

The dataavailable event is fired when the MediaRecorder delivers media data to your application for its use. The data is provided in a Blob object that contains the data. This occurs in four situations:

  • When the media stream ends, any media data not already delivered to your ondataavailable handler is passed in a single Blob.
  • When MediaRecorder.stop() is called, all media data which has been captured since recording began or the last time a dataavailable event occurred is delivered in a Blob; after this, capturing ends.
  • When MediaRecorder.requestData() is called, all media data which has been captured since recording began or the last time a dataavailable event occurred is delivered; then a new Blob is created and media capture continues into that blob.
  • If a timeslice property was passed into the MediaRecorder.start() method that started media capture, a dataavailable event is fired every timeslice milliseconds. That means that each blob will have a specific time duration (except the last blob, which might be shorter, since it would be whatever is left over since the last event). So if the method call looked like this — recorder.start(1000); — the dataavailable event would fire after each second of media capture, and our event handler would be called every second with a blob of media data that's one second long. You can use timeslice alongside MediaRecorder.stop() and MediaRecorder.requestData() to produce multiple same-length blobs plus other shorter blobs as well.

The Blob containing the media data is available in the dataavailable event's data property.

Syntax

MediaRecorder.ondataavailable = function(event) { ... }
MediaRecorder.addEventListener('dataavailable', function(event) { ... })

Example

...

  mediaRecorder.onstop = function(e) {
    console.log("data available after MediaRecorder.stop() called.");

    var audio = document.createElement('audio');
    audio.controls = true;
    var blob = new Blob(chunks, { 'type' : 'audio/ogg; codecs=opus' });
    var audioURL = window.URL.createObjectURL(blob);
    audio.src = audioURL;
    console.log("recorder stopped");
  }

  mediaRecorder.ondataavailable = function(e) {
    chunks.push(e.data);
  }

...

Specifications

Specification Status Comment
MediaStream Recording
The definition of 'MediaRecorder.ondataavailable' in that specification.
Working Draft Initial definition

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 47[2] 25.0 (25.0) No support No support No support
Feature Android Android Webview Firefox Mobile (Gecko) Firefox OS IE Phone Opera Mobile Safari Mobile Chrome for Android
Basic support No support No support 25.0 (25.0) 1.3[1] No support No support No support No support

[1] The intial Firefox OS implementation only supported audio recording.

[2] To try this feature on Chrome, enable Experimental Web Platform features from chrome://flags . Currently only video is supported, not audio.

See also

Document Tags and Contributors

 Contributors to this page: Sheppy, jpmedley, Sebastianz, chrisdavidmills, teoli, kscarfone
 Last updated by: Sheppy,