Here is a link to loop a youtube video:
Copy and Paste the URL above into the *Address Bar of your Web Browser. Then Copy the Video ID from the video of your choice. Paste the ID into the URL above replacing the Video ID with the actual Video ID from the video your choice. Then press "enter" to play the video.
Example of the Video ID - https://www.youtube.com/watch?v=TMTpVlQF8uU
NOTE * about the Address Bar -