There are a lot of YouTube videos, and more every second. In 2015, YouTube said people were uploading some 400 new hours of video every minute, and there’s no doubt its only gone up. So how do you make sure that every single video has its own unique link? Base 64.
As Tom Scott explains, YouTube’s video ID numbers—https://www.youtube.com/watch?v=gocwRvLhDf8—pack a lot of data into just a few characters. What you see bolded there is actually a base-64 number. Instead of being limited to numerals 0-9 like base-10 numbers are, a base-64 number can also use the entire alphabet in both lowercase and uppercase plus two symbols, which lets it pack an absurd amount of data into a small amount of space and generate a mind-blowingly large number of unique, random IDs.
At the current length of 11 characters, YouTube has some 73,786,976,294,838,206,464 URLs to work with. Or as Tom Scott puts it, enough for everyone on Earth to upload one video every minute for thousands of years. Suffice it to say, that’s enough. And even if it’s somehow not, one extra digit would give you two additional orders of magnitude. Yeah I think we’ll be fine.
Source: Tom Scott