SMPlayer Support Forum

Such as...
https://www.youtube.com/watch?v=ZafS4fWNKoY

Seems SMtube can't find the video, but I can open the link with SMPlayer and everything else.

If you want to download that video, there's a button in smtube that allows to enter a URL to be downloaded. I tested your URL and it works.

It seems some people entered URLs in the search field. That worked by chance and it doesn't work for all URLs.