The opening scene in this year’s Warren Miller ski film, “All Time,” begins with grainy black-and-white ski footage and narration intended to emulate the movie-house newsreels of the 1900s. After a brief overview of the roots of skiing, the narrator introduces the man who created the ski film genre more than 70 years ago. “A beach bum named Warren Miller decided windburn was better than sunburn, and noticed that toting a camera around the mountain got him a lot of dates,” the narrator says.