In order to download or convert video or audio you need to have a valid link. Here are examples of the correct links for each supported site.
This online video converter allows you to download video and then convert not only YouTube to mp3, but it supports YouTube, Dailymotion, Vimeo, Facebook, Metacafe, VK, SoundCloud, Instagram, AOL, Vevo, Google Drive, Twitter.
Web-site: https://www.youtube.com/
Web-site: https://www.dailymotion.com/
Web-site: https://vimeo.com/watch
Web-site: https://www.facebook.com/
Web-site: http://www.metacafe.com
Web-site: https://rutube.ru/
Web-site: https://vk.com
Web-site: https://soundcloud.com
Web-site: https://www.instagram.com
Web-site: https://www.aol.com/video/
Web-site: https://twitter.com