Regex to match Youtube URLs (using Ruby)

I've created a regular expression in order to match Youtube URLs. As Youtube URLs starts with https://youtube.com and https://youtu.be, the following regex solves the problem:

/^(?:https?:\/\/)?(?:www\.)?youtu(?:\.be|be\.com)\/(?:watch\?v=)?([\w-]{10,})/

This regex will match:

But it won't match: