This is an experimental technology
Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future versions of browsers as the specification changes.

The MediaSource interface represents a source of media data for an HTMLMediaElement object. A MediaSource object can be attached to a HTMLMediaElement to be played in the user agent.


Constructs and returns a new MediaSource object with no associated source buffers.


Inherits properties from its parent interface, EventTarget.

MediaSource.sourceBuffers Read only
Returns a SourceBufferList object containing the list of SourceBuffer objects associated with this MediaSource.
MediaSource.activeSourceBuffers Read only
Returns a SourceBufferList object containing a subset of the SourceBuffer objects contained within SourceBuffers — the list of objects providing the selected video track,  enabled audio tracks, and shown/hidden text tracks.
MediaSource.readyState Read only
Returns an enum representing the state of the current MediaSource, whether it is not currently attached to a media element (closed), attached and ready to receive SourceBuffer objects (open), or attached but the stream has been ended via MediaSource.endOfStream() (ended.)
Gets and sets the duration of the current media being presented.


Inherits properties from its parent interface, EventTarget.

Creates a new SourceBuffer of the given MIME type and adds it to the MediaSource's SourceBuffers list.
Removes the given SourceBuffer from the SourceBuffers list associated with this MediaSource object.
Signals the end of the stream.

Static methods

Returns a Boolean value indicating if the given MIME type is supported by the current user agent — this is, if it can successfully create SourceBuffer objects for that MIME type.


The following simple example loads a video chunk by chunk as fast as possible, playing it as soon as it can. This example was written by Nick Desaulniers and can be viewed live here (you can also download the source for further investigation.)

var video = document.querySelector('video');

var assetURL = 'frag_bunny.mp4';
// Need to be specific for Blink regarding codecs
// ./mp4info frag_bunny.mp4 | grep Codec
var mimeCodec = 'video/mp4; codecs="avc1.42E01E, mp4a.40.2"';

if ('MediaSource' in window && MediaSource.isTypeSupported(mimeCodec)) {
  var mediaSource = new MediaSource;
  //console.log(mediaSource.readyState); // closed
  video.src = URL.createObjectURL(mediaSource);
  mediaSource.addEventListener('sourceopen', sourceOpen);
} else {
  console.error('Unsupported MIME type or codec: ', mimeCodec);

function sourceOpen (_) {
  //console.log(this.readyState); // open
  var mediaSource = this;
  var sourceBuffer = mediaSource.addSourceBuffer(mimeCodec);
  fetchAB(assetURL, function (buf) {
    sourceBuffer.addEventListener('updateend', function (_) {
      //console.log(mediaSource.readyState); // ended

function fetchAB (url, cb) {
  var xhr = new XMLHttpRequest;'get', url);
  xhr.responseType = 'arraybuffer';
  xhr.onload = function () {


Specification Status Comment
Media Source Extensions
The definition of 'MediaSource' in that specification.
Candidate Recommendation Initial definition.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 23-webkit
25.0 (25.0)[1]
42.0 (42.0)
11[2] 15 8
Feature Android Firefox Mobile (Gecko) Firefox OS (Gecko) IE Phone Opera Mobile Safari Mobile
Basic support 4.4.4


41.0 11 30 No support

[1] Available after switching the about:config preference media.mediasource.enabled to true. In addition, support was limited to a whitelist of sites, for example YouTube, Netflix, and other popular streaming sites. The whitelist was removed and Media Source Extensions was enabled by default in 42+ for all sites.

[2] Only works on Windows 8+.

See also


© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.

API Audio audio Experimental Expérimental Extensions Interface Media MediaSource MSE Reference source Source Video video