When a video element has the inline and muted attributes set in Safari on iOS, there is no way to unmute the video using the video element controls. For custom players with a mute button, it is possible to toggle the muted state of the video element, but if the video is muted and the user taps to enter fullscreen after playback starts, there is no way to unmute the video while in fullscreen mode. The video element's volume is always 1 on iOS and there seems to be no event that lets the video element know that the user has adjusted the system volume. The best one can do is to unmute the video when the `webkitbeginfullscreen` event is raised to ensure the user has control of audio, but we can't infer that the user wants to hear audio just by their choice to enter fullscreen. The use case for this is with autoplay, where videos have to be muted for playback to start without user interaction.
<rdar://problem/28898596>