Google Search for many queries and search result pages shows a video box that takes searchers to videos mostly on YouTube but other platforms as well. Now, Google is testing playing those videos directly in the search results page and not taking you to YouTube.com or the site the video is hosted on.
Mordy Oberstein captured this and posted some screenshots on Twitter.
Notice the expand arrows icon:
Then when you click on it, it loads this overlay:
Forum discussion at Twitter.