Back in December, Facebook started testing auto-playing video ads, where video advertisements start playing in your feed without you having to click or tap play. Today, it introducing those ads to users across Facebook.
Photo by Thos003
Facebook has offered video ads for some time now. It's really the auto-play feature that's new. According to Facebook, video ads download only when you're connected to Wi-Fi, though they may play no matter what your connection status. The ads will start playing with no sound until you click or tap on them, at which point they will unmute and you can expand them.
At this point, it's unclear if there's a way to opt out of auto-playing video ads, though if you're on a desktop browser, you may be able to get rid of them with a tool like AdBlock.
Premium Video Ads on Facebook [Facebook for Business]