KitePlayerMediaSession
Mirrors player into the browser's media session and routes its buttons back.
That session is what the operating system's media overlay, the keyboard's media keys and a headset read for a page. Browsers show it only while the page plays sound through an audio or video element. KitePlayer plays through Web Audio, which no browser counts today, so the overlay appears only if the page also plays through such an element.
Artwork is a URL here, because that is the only form a browser takes. The item's own cover shows when the page sets none, from a URL made for its bytes (#425). Close it with the player. A button press that arrives after the player closed does nothing.
Parameters
how far the skip back and skip forward actions move when the browser names no offset of its own. Positive.