browser-mpris2 is an extension that implements a MPRIS v2 interface for Google Chrome and Chromium web browsers, which currently only supports YouTube. Using it you get YouTube media player controls (play, pause, stop and seeking) in MPRIS2-capable applets. For example, if you use Gnome Shell, you get YouTube media player controls as a permanent notification or, you can use an extension like Media Player Indicator for this. In Cinnamon / Linux Mint with Cinnamon, it shows up in the Sound Applet.