Google released Chrome 66 just over two weeks ago. The highlight was that content with sound no longer starts playing unexpectedly until you hit play. Autoplaying content that is muted still plays automatically, but autoplaying content with audio will only start if Chrome has determined that you tend to play content on that site.

Google is trying to strike a balance between forcing you to hit play when you shouldn’t have to and disabling content on websites that automatically play content with sound that you weren’t expecting. Chrome product manager John Pallett, who apparently also has “media muter” in his title, revealed today that “the new policy blocks about half of unwanted autoplays.”

Pallett also shared that “a significant number” of autoplays are paused, muted, or have their tab closed within six seconds by Chrome users. He didn’t say how many exactly, as the number varies significantly from site to site. But that shouldn’t surprise anyone, given how much work Google put into this latest feature.

Chrome decides which autoplaying content to stop in its tracks by learning your preferences and ranking each website according to your past behavior. If you don’t have browsing history with a site, Chrome allows autoplay for over 1,000 sites where Google says the highest percentage of visitors play media with sound (sites where media is the main point of visiting the site). As you browse the web, Chrome updates that list by enabling autoplay on sites where you play media with sound during most of your visits, and disables it on sites where you don’t.

More specifically, Chrome for desktop has a Media Engagement Index (MEI) that measures your propensity to consume media for each site you visit. You can check your MEI for all sites by pasting “chrome://media-engagement” into the address bar to reach your internal page.

The MEI is determined by a ratio of visits to significant media playback events per origin, determined by these four factors:

  • Consumption of the media (audio/video) must be greater than 7 seconds.
  • Audio must be present and unmuted.
  • Tab with video is active.
  • Size of the video (in px) must be greater than 200×140.

Google justifies all this work by noting that unexpected media playback is “one of the most frequent user concerns” because it “can use data, consume power, and make unwanted noise while browsing.” This change, Google argues, also unifies desktop web behavior with mobile, where autoplaying isn’t allowed.

If you are using Chrome 66 or higher, you already have this autoplaying policy. You should also keep in mind that as of Chrome 64, Google’s browser has an option to completely disable audio on a per-site basis (just right-click the tab in question and choose “Mute site”).