I am using the following regex for validating youtube video share url\'s.
var valid = /^(http\\:\\/\\/)?(youtube\\.com|youtu\\.be)+$/; alert
I tried this one and it works fine for me.
(?:http(?:s)?:\/\/)?(?:www\.)?(?:youtu\.be\/|youtube\.com\/(?:(?:watch)?\?(?:.*&)?v(?:i)?=|(?:embed|v|vi|user)\/))([^\?&\"'<> #]+)
You can check here https://regex101.com/r/Kvk0nB/1