MediaSource

MediaSource是Media Source Extensions API 表示媒体资源HTMLMediaElement对象的接口。MediaSource 对象可以附着在HTMLMediaElement在客户端进行播放。

Constructor

MediaSource()

构造并且返回一个新的MediaSource的空对象（with no associated source buffers）。

属性

从父接口EventTarget上继承而来。

MediaSource.sourceBuffers 只读

返回一个SourceBufferList 对象，包含了SourceBuffer的列表objects associated with this MediaSource.

MediaSource.activeSourceBuffers 只读

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.

MediaSource.readyState 只读

Returns an enum representing the state of the current MediaSource, whether it is not currently attached to a media element (closed), attached and ready to receive SourceBuffer objects (open), or attached but the stream has been ended via MediaSource.endOfStream() (ended.)

MediaSource.duration

Gets and sets the duration of the current media being presented.

Methods

Inherits properties from its parent interface, EventTarget.

MediaSource.addSourceBuffer()

Creates a new SourceBuffer of the given MIME type and adds it to the MediaSource's SourceBuffers list.

MediaSource.removeSourceBuffer()

Removes the given SourceBuffer from the SourceBuffers list associated with this MediaSource object.

MediaSource.endOfStream()

Signals the end of the stream.

Static methods

MediaSource.isTypeSupported()

Returns a Boolean value indicating if the given MIME type is supported by the current user agent — this is, if it can successfully create SourceBuffer objects for that MIME type.

Examples

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 (_) {
      mediaSource.endOfStream();
      video.play();
      //console.log(mediaSource.readyState); // ended
    });
    sourceBuffer.appendBuffer(buf);
  });
};

function fetchAB (url, cb) {
  console.log(url);
  var xhr = new XMLHttpRequest;
  xhr.open('get', url);
  xhr.responseType = 'arraybuffer';
  xhr.onload = function () {
    cb(xhr.response);
  };
  xhr.send();
};

Specifications

Browser compatibility

[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

• SourceBuffer
• SourceBufferList