Listening for video playback within a WKWebView

I’m currently working on an app for a client where certain features are disabled when a video starts to play. Specifically, a video that’s embedded in a WKWebView.

One way of doing this would be to inject Javascript into the page like I’ve written about before and let that attach listeners to every <video> tag on the page. When a video changes its play state our listener could post a message to the app via webkit.messageHandlers[_HANDLER_].postMessage(_OBJECT_); and we would need a handler in the app to do whatever it is we want it to do.

That's a little messy.

When a video starts to play in a WKWebView the <video> is replaced by the native video player. However, within the app we can’t get a reference to this video component in order to query its playing state, so I wondered if maybe this might just fire an NSNotification we could listen for.

I couldn’t find any documentation for this so I decided to listen for all notifications and see if I could find one that would do the trick.

To do that I added a notification center observer with no specific name, which translates to give me ALL of the notifications:

[[NSNotificationCenter defaultCenter] addObserverForName:nil
  object:nil
  queue:nil
  usingBlock:^(NSNotification* notification) {
    NSLog(@"Notification:\n"\
    "name: %@\n"\
    "object: %@\n"\
    "userInfo: %@",
    notification.name,
    notification.object,
    notification.userInfo);
  }];

Clearing the console before tapping play on the video led me to find that there actually is a notification that gets fired from the web view — its called SomeClientPlayingDidChange.

Inside the notification’s userInfo dictionary lies an IsPlaying key, with exactly what we want.

This meant that now we could add an observer for this notification and a handler to do whatever it is we need to do:

// Listen for video playback
[[NSNotificationCenter defaultCenter] addObserver:self 
  selector:@selector(videoPlayingDidChange:) 
  name:@"SomeClientPlayingDidChange" 
  object:nil];

// Video playing state handler
- (void)videoPlayingDidChange:(NSNotification *)notification
{
  BOOL isPlaying = [notification.userInfo[@"IsPlaying"] boolValue];
  // Do stuff with this newfound knowledge
}

Caveats: this notification doesn’t appear to be documented and could change at any time. It probably will. At the time of writing this works on iOS 8.x/9.x - however since we’re simply listening to the notification, the app might lose this functionality but shouldn’t lead to any crashes.