Diegetic sound refers to any audio that is present within the visuals of a trailer, such as dialogue between characters or ambient sounds. This helps audiences understand relationships and set the atmosphere. Non-diegetic sound includes music and effects that are not visually source, which help create suspense. Voiceovers are sometimes used in comedies and animations to convey jokes or the plot, as graphics alone may not be enough to engage audiences in the short trailer format. Dan Skinner explains that voiceovers were once common but are now less so, as trailers rely more on visuals to lead viewers through the content.