from https://bugzilla.mozilla.org/show_bug.cgi?id=480376
> It's not too uncommon for videos to have no audio track. It would be really > nice if the video controls could indicate this, so that users know why there's > no sound ("is something broken? is my volume too low? wtf?"). > > Unfortunately this info isn't available through the media element API, so this > would need to be added to the HTML5 spec. The simplest way to expose this > would > be as |readonly boolean hasAudio|. Is the media backend capable of determining > this this? we need a hasAudio JS only property for video element