Remove iOS 12 default volume GUI overlay?

On iOS 11, you managed to disable the default volume overlay, but when I updated to iOS 12, everytime I adjust the volume of a video, it shows the giant volume UI in the center of the screen. I know it’s possible to fix this, because the Twitch app on iOS 12 has its own volume UI instead of the default. I’m logging this as a problem instead of an idea because the current condition differs from your intended design.