Google’s (s GOOG) Chrome browser recently introduced little loudspeaker icons to tell you which tab is playing audio or video. It’s a neat feature, especially if you have lots of tabs open and one of them suddenly starts to auto-play an annoying ad at full volume. But how does the browser actually know this? It’s a fascinating question, and the answer has a lot to do with the evolution of media playback on the web.

Multimedia hacker Mike Melanson has the entire backstory to this in a fascinating little post on his website that also explains why this new approach is a lot easier for developers. Check it out if you want to read a neat piece of multimedia geekery.

Essentially, there are two ways media is being presented online: Publishers either rely on third-party plugins like Flash, or use HTML5 instead to play audio or video natively in the…