Click the flag and you get a youtube video ID. Of course, not all of these are real videos and you need to add the first part of a URL. But there are 64 different characters and the string is 11 charatcers long so therefore, you get 73786976294838206464 unique video IDs
You could also do this with scratch projects, (this project's ID is 9 numbers long) and it should be easier as it is only numbers.
