Justin Bieber explains his 'waddle' in trailer for 'Believe' At the end of the day, it comes down to a young man in a room writing a song. So claims one of Justin Bieber's associates in a trailer for the pop singer's new concert film, to which Pop & Hiss says: Come on, now. The songs matter, certainly, and Bieber's written or sung plenty of great ones, including several in his so-called Music Mondays series, in which he's releasing a new tune every week through next month. "PYD," a promising -- and evidently Michael Jackson-inspired -- collaboration with R. Kelly, is due Sunday at midnight. But to suggest that what drives Bieber's fame is the idea of his feverishly scrawling lyrics on a notepad -- that his process is what we really want to know about -- is, of course, absurd. Fortunately, the rest of the trailer for "Justin Bieber's Believe," which follows successful concert films from One Direction and Katy Perry and is scheduled to open Dec. 25, focuses on the important stuff: his battles with the paparazzi, his new mustache (it's "to make me feel a little bit older," he says) and, perhaps most important, the effect that wearing drop-crotch pants has on one's gait. "Sometimes I walk the way I walk -- I waddle -- because my pants are low," he tells an interviewer, before adding, "Don't let the pants wear you." Watch the trailer below.