Video: IPv4, the internet address system born out of the birth of the internet, serves as a cautionary tale to always plan ahead: no-one thought there would ever be more than 4.3 billion devices connected to the internet, only to be proved horribly wrong 30 years later. But YouTube planned ahead. Tom Scott explains the maths behind YouTube's video ID, the string of 11 characters in every YouTube URL that identifies one specific video. It's counted in base 64, meaning YouTube can squeeze 73,786,976,294,838,206,464 IDs into just 11 characters. That means YouTube won't be running out of IDs for quite some time.