Google Chrome is testing a new feature called Global Media Controls that allows you to open a small overlay window that contains playback controls and information about a YouTube video you are watching. The feature is currently in development for Windows, Linux, and Mac versions of the Chrome browser. At this point, it appears to only work with YouTube videos and it does not matter if its embedded or being watched directly on YouTube.com. In tests conducted by BleepingComputer, this feature is in very early development and will crash often.
Source: https://www.bleepingcomputer.com/news/software/google-chrome-tests-new-play-controls-for-youtube-videos/