MediaSource: activeSourceBuffers property
  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.
Value
  A SourceBufferList containing the SourceBuffer objects
  for each of the active tracks.
Examples
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). The function getMediaSource(), which is not defined here, returns a MediaSource.
js
const mediaSource = getMediaSource();
function sourceOpen() {
  console.log(mediaSource.readyState); // open
  const sourceBuffer = mediaSource.addSourceBuffer(mimeCodec);
  fetchAB(assetURL, (buf) => {
    sourceBuffer.addEventListener("updateend", () => {
      mediaSource.endOfStream();
      console.log(mediaSource.activeSourceBuffers);
      // will contain the source buffer that was added above,
      // as it is selected for playing in the video player
      video.play();
      console.log(mediaSource.readyState); // ended
    });
    sourceBuffer.appendBuffer(buf);
  });
}
// …
Specifications
| Specification | 
|---|
| Media Source Extensions™  # dom-mediasource-activesourcebuffers  | 
Browser compatibility
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