Update June 2021. YouTubeDouber has retired
Head over to YouTube Doubler and paste in the URLs of the first and second YouTube video as indicated in the screenshot above. You have the option to edit the start time if you want your videos to start at a certain time. Next, click on ‘Double up’ button and you are done. Give it a try and see what you can do with it. Check out this post from MakeUseof to learn more about other handy YouTube tips. Enjoy