There’s nothing wrong with a musical playing it straight. Marc Anthony wears the pants and his producer/co-star and wife, Jennifer Lopez, sticks to dresses in El Cantante. But there’s no kick in this by-the-numbers biopic, in which Anthony plays Héctor Lavoe, a salsa singer from Puerto Rico who hit Manhattan in the 1960s and became a global sensation until cocaine, heroin and complications from AIDS ravaged his voice by 1985 and finally ended his life in 1993. Lopez plays Héctor’s hectoring wife, Puchi, who tells his story in flashback. What a downer. El Cantante (“The Singer”) unfolds like every dreary Hollywood saga about a star’s fall. Director/cowriter Leon Ichaso (Piñero), failing to make the vital connection between Hector’s life and his art, focuses on the domestic battles. The louder Puchi yells, the more Hector recedes. The film comes alive only when the singer sings, especially when matched on the Fania label with trumpet maestro Willie Colón (John Ortiz). The gifted Anthony invests Lavoe’s music with a passion that honors both their talents.