YouPause

Allows to control YouTube videos using hotkeys. By default use Ctrl+Shift+1 to pause all running YouTube videos in all tabs; Ctrl+Shift+2 to resume previously paused videos; Ctrl+Shift+3 and Ctrl+Shift+4 allow to move through videos in a playlist.
Hotkeys are customizable in Chrome Keyboard Shortcuts settings (chrome://extensions/shortcuts)

What is new in version 4.1:
* added two new hotkeys to navigate to next/prev video in a playlist

What is new in version 4.0:
* a Popup window with a list of paused videos (click on the extension's button in Chrome to see it)
* an option to disable notifications
* fixed some bugs
* Google Analytics tracking