Chrome will eventually block unwanted autoplay videos for all users as part of a new policy that Google has set for the browser. For anyone who tends to stop autoplaying videos as soon as they start, this is a nifty little change that will make the browsing experience that much better, and serves as an additionally beneficial feature to the changes that Google made with filtering out specific ads that would be deemed harmful to the user's enjoyment while browsing. One thing to note, however, is that blocking unwanted autoplay videos won't be an immediate thing.
While Google is rolling this change out right away, Chrome will first need to learn you preferences for autoplaying videos, meaning you'll have to browse some websites first with autoplaying videos and over time when it recognizes that you're stopping these videos, it'll start to block them from playing automatically. Google doesn't mention how long it will take before these changes are implemented, so it could take a few days or it could take weeks, though it likely just depends on how often you browse and how many sites you're visiting that have videos which play automatically. The more you browse and the more you stop autoplaying videos that you encounter, chances are the quicker Chrome will start to block them for you.
Google states that if you have no browsing history whatsoever, Chrome will allow videos to autoplay from over 1,000 sites where it notices that visitors to those sites are playing media that comes with sound. So eventually as you visit more sites then Chrome will start to pick up on the fact that you're not playing media with sound on these sites, and thus you should end up with a more personalized browsing experience where autoplaying videos will be blocked unless you want them to play. Google says that this is already a live change in the most recent version of Chrome, so if you're not updated then you'll want to do that first, after which you should start to see the changes.