YouTube
From Tardis Wiki, the free Doctor Who reference
YouTube was a website on the Internet on Earth in the 21st century.
After a wave of Shakri cubes arrived on Earth, people posted about them on YouTube. (TV: The Power of Three)
ReAL wORLD
In the real world, the Twelfth Doctor title sequence was created by fan of the show, Billy Hanshaw. Steven Moffat was impressed with the conceptual opening sequence that was popular on YouTube; liking how original it was, he got in contact with Hanshaw for creating an official title sequence.
