The addSourceBuffer() method of the MediaSource interface creates a new SourceBuffer of the given MIME type and adds it to the MediaSource's sourceBuffers list. The new SourceBuffer is also returned.


var sourceBuffer = mediaSource.addSourceBuffer(mimeType);


A DOMString specifying the MIME type of the SourceBuffer to create and add to the MediaSource.

Return value

A SourceBuffer object representing the new source buffer that has been created and added to the media source.


The value specified for mimeType is an empty string rather than a valid MIME type.
The MediaSource is not in the "open" readyState.
The specified mimeType isn't supported by the user agent, or is not compatible with the MIME types of other SourceBuffer objects that are already included in the media source's sourceBuffers list.
The user agent can't handle any more SourceBuffer objects, or creating a new SourceBuffer using the given mimeType would result in an unsupported configuration of SourceBuffers.


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

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


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

Browser compatibility

BCD tables only load in the browser

See also