The Chrome browser is finally muting the sound of autoplay videos by default. The update, in Chrome version 66, has arrived three months later than planned.

During that delay period, users were able to actively choose to mute all autoplay videos on a specific site. Now that will not only be the default, but the idea is that videos with sound won’t even start playing. (Those without sound will still autoplay.)

Rather than put the onus on the user to select exceptions to this rule, Chrome will attempt to create automated exceptions using a “Media Engagement Index.” In simple terms, if you regularly choose to watch videos on a site, Chrome will let the autoplay and sound work on future visits.

For the purposes of these calculations, Chrome will only count you as intentionally watching a video if you do so for more than seven seconds, have the sound switched on, and have the relevant tab active. It won’t count videos that are smaller than 200 x 140 pixels.

Even if a site does get on the exceptions list through these calculations, you can still actively choose to mute it from the menu that appears when you right-click on the tab at the top of the screen.

On mobile devices, the set-up is simpler. Sites will only be automatically excepted from the rule if you have added a link to it on your home screen.

It’s worth noting in both cases that once you actively click or tap on a web page, other pages on the same site will be allowed to autoplay videos for the rest of that browsing session, unless you’ve actively chosen to mute the site.

Meanwhile a small proportion of computers running Chrome 66 will trial a new security tool called Site Isolation. In simple terms it means all pages from a particular website will be put into a separate sandboxed process. The idea is to make it even harder for rogue sites to access a user’s data from other websites.