Oscar winners were busy on all fronts at the Brooklyn Academy of Music the other night. While Cate Blanchett performed in her critically acclaimed production of “A Streetcar Named Desire,” Sam Mendes was rehearsing Shakespeare’s “Hamlet” and “The Tempest,” which both open in January, and Pedro Almodovar was introducing his latest movie, “Broken Embraces,” starring Penelope Cruz at the BAM Rose Cinemas before rushing over to the Harvey Theatre to catch Blanchett in “Streetcar.”