I am having trouble getting chrome to autoplay a video. I have set the video to muted and it auto plays in both Safari and Firefox but not chrome.
The example below, with minimal change from your code, plays in chrome (Version 62.0.3202.94 ) on a Mac (10.12.6):
It may be that Safari and Friefox are playing the mp4 and chrome the webm, and the issue related to the webm video itself rather than your HTML5 code.