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This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

The activeSourceBuffers read-only property of the MediaSource interface 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.


var myActiveSourceBuffers = mediaSource.activeSourceBuffers;


A SourceBufferList.


The following snippet is based on a simple example written by Nick Desaulniers (view the full demo live, or download the source for further investigation.)

function sourceOpen (_) {
  //console.log(this.readyState); // open
  var mediaSource = this;
  var sourceBuffer = mediaSource.addSourceBuffer(mimeCodec);
  fetchAB(assetURL, function (buf) {
    sourceBuffer.addEventListener('updateend', function (_) {
      // will contain the source buffer that was added above,
      // as it is selected for playing in the video player
      //console.log(mediaSource.readyState); // ended



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

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support


23 — 31 -webkit-



25 — 421 2

FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support3333 Yes4130 No ?

1. Limited support to a whitelist of sites, for example YouTube, Netflix, and other popular streaming sites. The whitelist was removed when Media Source Extensions was enabled by default in Firefox 42.

2. From version 25 until version 42 (exclusive): this feature is behind the media.mediasource.enabled preference. To change preferences in Firefox, visit about:config.

3. Only works on Windows 8+.

See also

Document Tags and Contributors

 Contributors to this page: fscholz, libbymc, chrisdavidmills
 Last updated by: fscholz,