How to pin a video to watch independently from Safari tabs There's a feature on Touch Bar in MacBook Pro which allows you to pin the video in Safari and watch it even after changing to another tab. 
Here is the button in the Touch Bar:



What's the shortcut for this? How can I do the same in my MacBook Air with no Touch Bar?
This is called Picture in Picture mode. Using it, you can watch video in a floating frame which remains on top of all windows and is available on all the Spaces.

Picture in Picture mode is a macOS feature available on all Macs running macOS Sierra and later. It doesn't require dedicated hardware such as a Touch Bar to function. Touch Bar merely gives a handy shortcut to enter Picture in Picture mode.


Watch video using Picture in Picture on your Mac



  If you don't see a Picture-in-Picture button, hold down the Control key and double-click inside the video to open a shortcut menu. Then choose Enter Picture-in-Picture, if available.


This shortcut relies on using both keyboard and mouse.