It’s the CGI work of Alex Roman, an enigmatic artist who specialises in photorealistic computer graphics. You can watch this as many times as you like and still not believe that it’s artificial.
If you’re as stunned as we are by this, then the best thing to do is watch this, and wonder where the last twelve minutes and twenty nine seconds went. (On his website Roman also has a “making of” rundown of his techniques.)
Meanwhile, we’re left wondering how much longer we’ll need physical sets and actors at all.
PS: We've done a little research on Alex Roman and according to the Blender forum he uses Autodesk 3DS Max, Chaos Software's V-Ray and Adobe After effects, although apparently you can achieve similar quality with Blender + Yafaray / Luxrenderer Open Source alternatives.