Ever open a YouTube video in a new tab, only to find that it’s started playing without you? Or a page that starts playing music before you’re ready? Chrome’s latest update will now mute those by default, until you navigate to the tab yourself.
This feature, currently available in Chrome's dev channel (version 46), is really handy. Building off the tab-muting button that came to Chrome last year, Chrome will now automatically mute any media that's set to auto-play. It will still load it, though, and once you click on the tab, it will start playing. (If you navigate away from the tab, it will keep playing -- so don't worry about being able to play music or videos in the background).
This feature should be enabled automatically, so make sure you're on the latest version to try it out. If you're using a channel other than Dev, you can switch to the Dev channel here.
Chrome Will No Longer Autoplay Video in Background Tabs [OMG! Chrome!]