Selectext is the best text-copying tool in the Chrome Store. You can easily copy and paste text from videos or lectures, even if the source is on another site. Use it on YouTube, Udemy, Sharepoint, or any video site. 

Copy the text by pausing the video and tapping the text you want to copy. You can also use the arrow keys to move the cursor around. It works with all sites except some Flash videos.

It supports 50+ languages and is the only text-copying tool that works with handwritten text.

It will only work on videos that are playing. You'll get a pop-up that shows you when it's working and when it's not.

It also supports multiple selections by holding the control button on Windows or the command button on Mac.

You can turn the feature off or on on any site.