Until today, the YouTube videos were played with software and additional extension but now it will not happen. Google has introduced loop feature on the YouTube, which when activated make the videos play again and again. If you click of video there will be option of menu on the right side, which also include additional options, where the loop option is activated. This makes the video to play again and again.

Now Play Videos on YouTube without Software and additional extension

This feature is only for desktop users for now. Hopefully, it will roll out for mobile user very soon.