Detect when a webview video becomes fullscreen on ios8

This is the work around I found for this..

[[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(VideoExitFullScreen:)
                                                 name:UIWindowDidBecomeVisibleNotification
                                               object:self.view.window];

[[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(VideoEnterFullScreen:)
                                                 name:UIWindowDidBecomeHiddenNotification
                                               object:self.view.window];

update for Swift 4.2, iOS 12.1 and WKWebView:

override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)

    // listen for videos playing in fullscreen
    NotificationCenter.default.addObserver(self, selector: #selector(onDidEnterFullscreen(_:)), name: UIWindow.didBecomeVisibleNotification, object: view.window)

    // listen for videos stopping to play in fullscreen
    NotificationCenter.default.addObserver(self, selector: #selector(onDidLeaveFullscreen(_:)), name: UIWindow.didBecomeHiddenNotification, object: view.window)
}

override func viewWillDisappear(_ animated: Bool) {
    super.viewWillDisappear(animated)

    // remove video listeners
    NotificationCenter.default.removeObserver(self, name: UIWindow.didBecomeVisibleNotification, object: view.window)
    NotificationCenter.default.removeObserver(self, name: UIWindow.didBecomeHiddenNotification, object: view.window)
}

@objc func onDidEnterFullscreen(_ notification: Notification) {
    print("video is now playing in fullscreen")
}

@objc func onDidLeaveFullscreen(_ notification: Notification) {
    print("video has stopped playing in fullscreen")
}

Swift 5.1:

NotificationCenter.default.addObserver(
    forName: UIWindow.didResignKeyNotification,
    object: self.view.window,
    queue: nil
) { notification in
    print("Video is now fullscreen")
}

NotificationCenter.default.addObserver(
    forName: UIWindow.didBecomeKeyNotification,
    object: self.view.window,
    queue: nil
) { notification in
    print("Video stopped")
}