Rather than putting a blanket block on everything, the browser keeps a list of sites the user has clicked to play a video previously and excludes them from the practice. This means sites like YouTube that use autoplay effectively won't be impacted.
It's a simple but effective way to block only the most annoying content. By default, the browser will autoplay videos with audio on just 1,000 popular sites. As your browsing history accumulates, it will tailor more to your preference.
“As you teach Chrome, you may find that you need to click ‘play' every now and then, but overall the new policy blocks about half of unwanted autoplays, so you will have fewer surprises and less unwanted noise when you first arrive at a website.” said Google product manager John Pallett.
Chrome 64 Blocking
Autoplay audio blocking was first introduced in Chrome 64. However, the feature simply let users permanently mute a website's audio. That's quite cumbersome and does little if you visit a lot of new sites.
The new iteration should gel better with Chrome 64's other additions, which included a better pop-up blocker, the removal of fake download buttons, and malicious auto-directs. Together, the features should make Chrome one of the least annoying apps to browse with.
In my testing, the feature has worked well, though it's still not the far-reaching solution some were hoping for. The feature doesn't block video from playing entirely once you click on a webpage, it just mutes the audio. This means news sites can still burn through your bandwidth and slow down your connection.
Unfortunately, Google is somewhat limited due to the use of HTML5 video to replace cumbersome GIFs. Even so, it would be nice to have the option there.