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.

mimeType

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

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

InvalidAccessError DOMException

Thrown if the value specified for mimeType is an empty string rather than a valid MIME type.

InvalidStateError DOMException

Thrown if the MediaSource is not in the "open" readyState.

NotSupportedError DOMException

Thrown if 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.

QuotaExceededError DOMException

Thrown if 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). The function getMediaSource(), which is not defined here, returns a MediaSource.

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

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

function sourceOpen() {
  console.log(this.readyState); // open
  const sourceBuffer = mediaSource.addSourceBuffer(mimeCodec);
  fetchAB(assetURL, (buf) => {
    sourceBuffer.addEventListener("updateend", () => {
      mediaSource.endOfStream();
      video.play();
      console.log(mediaSource.readyState); // ended
    });
    sourceBuffer.appendBuffer(buf);
  });
}

• SourceBuffer
• SourceBufferList