This plays well but no sound on iPhone7:
<video autoplay muted playsinline controls>
<source src="video.mp4" type="video/mp4">
<source src="video.webm" type="video/webm">
First one plays from the start button on full screen, no sound. Second plays well but no sound. Third plays well from the start button, with sounds.
Tested with iOS Safari and iOS Chrome.