Google Chrome Team is working on identifying tabs that play audio
in order to exclude them from the list of tabs to discard when memory runs out.
In a first step, they've added a small indicator on top of the tab favicon to tell when a tab is actually playing audio.
Youtube video work only if you joined the HTML5 trial at www.youtube.com/html5
You can already see it in the last chromium build (download-chromium.appspot.com