As Corden notes, the quality isn't always great (though it's pretty good), since most of the camera were off, but happily it was captured by those in the audience on their mobile phones!
It features actor Billy Porter who won the 2013 Tony award for Best Actor in a Musical, for his performance in Kinky Boots. To fill in the time, Corden offers him a book of songs to sing from, and he chooses "Everything's Coming Up Roses," from Gypsy. He insists he doesn't need the lyrics, though messes up a bit, but then he only expected to sing a few lines and...well, you can see what happens. It's great fun.