“Eroica!” follows the Eroica Trio (cellist Sara Sant'Ambrogio, pianist Erika Nickrenz and violinist Adela Pena) through a hectic year of touring, while also badgering composer Kevin Kaska to complete the triple concerto he's writing for them. The pressure on Kaska is enormous (Sant'Ambrogio: “Beethoven's the only one who has been able to do it”), and filmmaker Alan Miller's tight pacing makes it visceral.