Add middleware support. Middleware can function as go-between between the player and the tech. For example, it can modify the duration that the tech returns to the player. In addition, middleware allow for supporting custom video sources and types.
Currently, middleware can only intercept timeline methods like duration, currentTime, and setCurrentTime.
For example,
```js
videojs.use('video/foo', {
setSource(src, next) {
next(null, {
src: 'http://example.com/video.mp4',
type: 'video/mp4'
});
}
});
```
Will allow you to set a source with type `video/foo` which will play back `video.mp4`.
This makes setting the source asynchronous, which aligns it with the spec a bit more. Methods like play can still be called synchronously on the player after setting the source and the player will play once the source has loaded.
`sourceOrder` option was removed as well and it will now always use source ordering.
BREAKING CHANGE: setting the source is now asynchronous. `sourceOrder` option removed and made the default.
Prevent techs (and others) from being registered via registerComponent.
* `registerComponent` now throws if given an object that is not a subclass of Component (or Component itself).
* `registerComponent` now throws if given a non-empty string as its name argument.
BREAKING CHANGE: registerComponent now throws if no name or not a component is passed in.
Chrome has a bug where if you add a remote text track and try to use it programmatically, you won't get any cues displayed. So, just switch to always emulated mode.
Also, add IS_SAFARI and IS_ANY_SAFARI to the browsers.
Tech#addRemoteTextTrack now accepts a second parameter - a boolean named manualCleanup which defaults to true preserving backwards compatibility. When that value is set to false the text track will be removed from the video element whenever a source change occurs.
