IOS WKWebview Fullscreen Capture with Built-in Youtube Video

Question

IOS WKWebview Fullscreen Capture with Built-in Youtube Video

I searched a lot of time, I found some clues, but I cannot figure out how to apply this to my problem. Would thank for any help.

What is trying to achieve is quite straightforward:

My app includes WKWebview, which plays YouTube videos (with some text overlay). I added a link to take a screenshot and save it in a camera roll.

Result:

It works fine in the simulator, but on the device I can only see the result, which overlays the text and the background (it is assumed that this video) is black.

Here is my current code (SWIFT 3):

...
// Save screenshot
UIImageWriteToSavedPhotosAlbum(captureScreen(), nil, nil, nil)
...

func captureScreen() -> UIImage {
    UIGraphicsBeginImageContextWithOptions(webView!.bounds.size, webView!.isOpaque, 0)
    webView!.drawHierarchy(in: webView!.bounds, afterScreenUpdates: false)
    let image = UIGraphicsGetImageFromCurrentImageContext()!
    UIGraphicsEndImageContext()
    return image
}

I also tried (same result)

...
UIImageWriteToSavedPhotosAlbum(captureScreen(), nil, nil, nil)
...

func captureScreen() -> UIImage {
    let image = UIApplication.shared.screenShot!
    return image
}