For more details, please check out this documentation: https://developer.apple.com/library/safari/documentation/AudioVideo/Conceptual/Using\_HTML5\_Audio\_Video/Device-SpecificConsiderations/Device-SpecificConsiderations.html\#//apple\_ref/doc/uid/TP40009523-CH5-SW11
On the desktop, you can set and read the volume property of an or
element. This allows you to set the element’s audio volume relative to the computer’s current volume setting. A value of 1 plays sound at the normal level. A value of 0 silences the audio. Values between 0 and 1 attenuate the audio.
> This volume adjustment can be useful, because it allows the user to mute a game, for example, while still listening to music on the computer.