A voiceover is the non-diegetic use of a character or omnipresent narrator talking over the visuals of a film or television show. This voiceover can be existential, like in Terrence Malick movies, or it can be directly related to what’s happening on the screen, like in Casino. No matter which voiceover you use, you have to make sure it carries the story and doesn’t over-explain what we’ve already seen.