When the musicians marched, it was more of a walk at times, and they did not yet attempt portions of the halftime drill. But from the opening fight songs to Georgia Southern University’s alma mater, through Bruno Mars and a little Puccini, they played with spirit and seeming ease. At the conclusion of a grueling week known as band camp, the Southern Pride Marching Band put on a sneak preview of its 2013 debut shows Aug. 16.