MediaSource
===========

The **`MediaSource`** interface of the Media Source Extensions API represents a source of media data for an `HTMLMediaElement` object. A `MediaSource` object can be attached to a `HTMLMediaElement` to be played in the user agent.

EventTarget

MediaSourceConstructor
-----------

`MediaSource()`

Constructs and returns a new `MediaSource` object with no associated source buffers.

Instance properties
-------------------

`MediaSource.activeSourceBuffers` Read only 

Returns a `SourceBufferList` object containing a subset of the `SourceBuffer` objects contained within `MediaSource.sourceBuffers` — the list of objects providing the selected video track, enabled audio tracks, and shown/hidden text tracks.

`MediaSource.duration`

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

`MediaSource.handle` Read only  
Experimental

Inside a dedicated worker, returns a `MediaSourceHandle` object, a proxy for the `MediaSource` that can be transferred from the worker back to the main thread and attached to a media element via its `HTMLMediaElement.srcObject` property.

`MediaSource.readyState` Read only 

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.sourceBuffers` Read only 

Returns a `SourceBufferList` object containing the list of `SourceBuffer` objects associated with this `MediaSource`.

Static properties
-----------------

`MediaSource.canConstructInDedicatedWorker` Read only  
Experimental

A boolean; returns `true` if `MediaSource` worker support is implemented, providing a low-latency feature detection mechanism.

Instance methods
----------------

*Inherits methods from its parent interface, `EventTarget`.*

`MediaSource.addSourceBuffer()`

Creates a new `SourceBuffer` of the given MIME type and adds it to the `MediaSource.sourceBuffers` list.

`MediaSource.clearLiveSeekableRange()`

Clears a seekable range previously set with a call to `setLiveSeekableRange()`.

`MediaSource.endOfStream()`

Signals the end of the stream.

`MediaSource.removeSourceBuffer()`

Removes the given `SourceBuffer` from the `MediaSource.sourceBuffers` list.

`MediaSource.setLiveSeekableRange()`

Sets the range that the user can seek to in the media element.

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.

Events
------

`sourceclose`

Fired when the `MediaSource` instance is not attached to a media element anymore.

`sourceended`

Fired when the `MediaSource` instance is still attached to a media element, but `endOfStream()` has been called.

`sourceopen`

Fired when the `MediaSource` instance has been opened by a media element and is ready for data to be appended to the `SourceBuffer` objects in `sourceBuffers`.

Examples
--------

### Complete basic example

The following simple example loads a video with `XMLHttpRequest`, 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). The function `getMediaSource()`, which is not defined here, returns a `MediaSource`.


```js
const video = document.querySelector("video");

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"';
let mediaSource;

if ("MediaSource" in window && MediaSource.isTypeSupported(mimeCodec)) {
  mediaSource = getMediaSource();
  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
  const sourceBuffer = mediaSource.addSourceBuffer(mimeCodec);
  fetchAB(assetURL, (buf) => {
    sourceBuffer.addEventListener("updateend", () => {
      mediaSource.endOfStream();
      video.play();
      console.log(mediaSource.readyState); // ended
    });
    sourceBuffer.appendBuffer(buf);
  });
}

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

### Constructing a `MediaSource` in a dedicated worker and passing it to the main thread

The `handle` property can be accessed inside a dedicated worker and the resulting `MediaSourceHandle` object is then transferred over to the thread that created the worker (in this case the main thread) via a `postMessage()` call:


```js
// Inside dedicated worker
let mediaSource = new MediaSource();
let handle = mediaSource.handle;
// Transfer the handle to the context that created the worker
postMessage({ arg: handle }, [handle]);

mediaSource.addEventListener("sourceopen", () => {
  // Await sourceopen on MediaSource before creating SourceBuffers
  // and populating them with fetched media — MediaSource won't
  // accept creation of SourceBuffers until it is attached to the
  // HTMLMediaElement and its readyState is "open"
});
```


Over in the main thread, we receive the handle via a `message` event handler, attach it to a `<video>` via its `HTMLMediaElement.srcObject` property, and `play` the video:


```js
worker.addEventListener("message", (msg) => {
  let mediaSourceHandle = msg.data.arg;
  video.srcObject = mediaSourceHandle;
  video.play();
});
```


**Note:** `MediaSourceHandle`s cannot be successfully transferred into or via a shared worker or service worker.

Specifications
--------------

| Specification |
| --- |
| Media Source Extensions™ # mediasource |

Browser compatibility
---------------------

BCD tables only load in the browser with JavaScript enabled. Enable JavaScript to view data.

See also
--------

* `SourceBuffer`
* `SourceBufferList`