AutoPlay and Volume
with HTML 5 Audio and Video
Most mobile devices require human interaction / gesture through a physical touch/button on the device to launch a media file (e.g. autoPlay) or adjust the volume
Likewise, the "mute" and volume controls may not work as expected due to these device limitations.
Some hardware and/or browser manufacturers have decided to prevent certain kinds of functionality in order to make using the device and/or browser a "better" overall experience and perhaps to prevent exessive bandwith usage.
For example, if you're in church and are bored and decide to visit a web page with your phone. If the web page starts playing an AC/DC song "programmatically" when the page loads you'll be in BIG trouble.
Likewise, if the web page has a player on it and the only way to control the volume is through tiny inaccessible buttons (or maybe even no volume buttons), there would be no way to turn the volume down.
Or if every time you adjusted the physical device volume, the web page would programmatically turn the volume back up.... well that would suck.
A workaround for nerds
If you're handy with your mobile devices, you may be able to lift these restrictions according to information on this post: