It would be great if the <title> of a document (as displayed in its tab) would automatically get a prefix like ▶ if video or audio is currently playing in it. This would make it easier to track down which tab is making noise. http://soundcloud.com/ and http://hypem.com/ are popular sites that already do this through some scripting, but it would be very useful to have this kind of functionality baked into the browser. I do realize this would be hard to implement for media that’s playing through a plugin [1], but it would still be useful for <video> and <audio>. [1] https://bugzilla.mozilla.org/show_bug.cgi?id=626586#comments
I like the feature idea, but this is beyond the scope of WebKit. It would be a browser feature. You might consider reporting it to the browser(s) you have in mind if not filed already.