This is the first launch experience for the YouTube iPhone app. It starts with a one-screen value proposition slide in the style of Google’s other product offerings like Google Now, and prompts for sign in.
I skipped signing in and was shown 2 more intro screens with animated instructions on how to watch and dismiss videos using gestures. Tapping “Done” dropped me into the popular video stream. Interestingly, the gesture instructions were repeated in context when I viewed my first video, which I found to be much more effective than the abstracted intro screens. It seems like those might be unnecessary; just drop new users right into the popular video stream as quickly as possible.