Since sometime, for now, Chrome and Microsoft Edge (Chromium) browsers are displaying Media Controls Overlay if you use media keys while videos are playing, there is another development taken place, Microsoft worked with Google to bring YouTube album or video info to overlay. This can be spotted in latest Chrome Canary and Edge (dev and canary builds), even in Picture in Picture mode also.

If you’re using latest Chrome Canary or Edge Insider build, visit YouTube and play any video, while the video is playing, press media keys on keyboard such as Play/Pause or prev or next track or Volume to see an overlay appear on top of Chrome or Edge browser displaying metadata about video you’re viewing.
The overlay displays album’s name, thumbnail and company and media controls such as Previous, Pause and next buttons including volume bar, sometimes this is called as Volume OSD.

Microsoft Edge team member jumped onto a Reddit thread that discussed “YouTube thumbnails with Media Controls Overlay” and said he has worked with Google engineers to bring this feature to Edge and confirmed this feature is also available and working in latest Chrome Canary.
The media overlay can be annoying and intruding for some, the media session service and hardware media key handling features are responsible for the display banner and these features also cause media keys to stop working for Spotify or iTunes, we’ve covered how to disable these overlays here. Do take note these overlays appear only when you use media keys.