Here's how masterfully Sarah Polley manipulates tone in "Take This Waltz," just her second film as writer and director: She takes the Buggles' peppy '80s anthem "Video Killed the Radio Star," best known as the song that launched MTV, and finds unexpected poignancy in it. She actually uses it a couple of times in the film, in very different ways, and in both instances the mood she establishes is wistful and assured.