'Souvenir' enjoyably but dawdlingly traces career of infamously bad opera singer

Florence Foster Jenkins -- the socialite-turned-soprano -- has a solemn warm-up routine. Looking religiously intent, she flexes and massages her jaw. She touches her fingers delicately to her ribs, as if readying her breath support. She draws an invisible plumb line upwards from the top of her scalp, perhaps imagining that her posture aligns with a star. Then she, for lack of a better word, sings.