Template:YouTube

https://img.youtube.com/vi//default.jpg  Use this template like this:

The YouTube video ID is a list of characters. For example, in this video: http://www.youtube.com/watch?v=n9MtsaEqGvo

It's the last part of the URL,. The template would look like this:

The result is this:

The description part is not required. The title neither, but recommended.