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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 SourceBuffer interface represents a chunk of media to be passed into an HTMLMediaElement and played, via a MediaSource object. This can be made up of one or several media segments.


Inherits properties from its parent interface, EventTarget.

Controls how the order of media segments in the SourceBuffer is handled, in terms of whether they can be appended in any order, or they have to be kept in a strict sequence.
SourceBuffer.updating Read only
A boolean indicating whether the SourceBuffer is currently being updated — i.e. whether an SourceBuffer.appendBuffer(), SourceBuffer.appendStream(), or SourceBuffer.remove() operation is currently in progress.
SourceBuffer.buffered Read only
Returns the time ranges that are currently buffered in the SourceBuffer.
Controls the offset applied to timestamps inside media segments that are subsequently appended to the SourceBuffer.
SourceBuffer.audioTracks Read only
A list of the audio tracks currently contained inside the SourceBuffer.
SourceBuffer.videoTracks Read only
A list of the video tracks currently contained inside the SourceBuffer.
SourceBuffer.textTracks Read only
A list of the text tracks currently contained inside the SourceBuffer.
Controls the timestamp for the start of the append window. This is a timestamp range that can be used to filter what media data is appended to the SourceBuffer. Coded media frames with timestamps within this range will be appended, whereas those outside the range will be filtered out.
Controls the timestamp for the end of the append window.
Specifies the default values to use if kind, label, and/or language information is not available in the initialization segment of the media to be appended to the SourceBuffer.


Fired whenever SourceBuffer.appendBuffer() or SourceBuffer.appendStream() is ended by a call to SourceBuffer.abort()SourceBuffer.updating changes from true to false.
Fired whenever an error occurs during SourceBuffer.appendBuffer() or SourceBuffer.appendStream()SourceBuffer.updating changes from true to false.
Fired whenever SourceBuffer.appendBuffer() method or the SourceBuffer.remove() completes. SourceBuffer.updating changes from true to false. This event is fired before onupdateend.
Fired whenever SourceBuffer.appendBuffer() method or the SourceBuffer.remove() has ended. This event is fired after onupdate.
Fired whenever the value of SourceBuffer.updating transitions from false to true.


Inherits properties from its parent interface, EventTarget.

Appends media segment data from an ArrayBuffer or ArrayBufferView object to the SourceBuffer.
Appends media segment data from a ReadableStream object to the SourceBuffer.
Aborts the current segment and resets the segment parser.
Removes media segments within a specific time range from the SourceBuffer.


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 'SourceBuffer' in that specification.
Candidate Recommendation Initial definition.

Browser compatibility

Feature Chrome Edge Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 23 (Yes) 25.0 (25.0)[1]
42.0 (42.0)
11[2] 15 8
trackDefaults and appendStream() ? ? No support ? ? ?
Feature Android Edge Firefox Mobile (Gecko) Firefox OS (Gecko) IE Phone Opera Mobile Safari Mobile
Basic support 4.4.4 (Yes)

No support

No support 11 30 No support
trackDefaults and appendStream() ? ? No support No support ? ? 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