The first YouTube video is 18 seconds long.
Why it is true
It is called 'Me at the zoo', was uploaded by Jawed Karim (a co-founder), and shows him talking about elephants at a zoo.
Source: YouTube History
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.