It’s YouTube tool that you can control on the YouTube website. In the omnibox or in the workbar you see a gray lamp of the Turn Off the Lights browser extension. When you click on this lamp button it highlight automatically the video players on that page. And it supports video players such as YouTube, vimeo, Dailymotion, Youku, Apple Music etc. This is a unique and powerful tool in your web browser.
If you want test this it, you can it’s a FREE opensource browser extension where you can download it on this homepage.