In the Back to the Future clip, Marty McFly gets stuck in the year 1955 and is looking for someone to help him get back to his original year of 1985. The person who Marty ends up recruiting to help him is the man who sent him back there in the first place, Doc Brown. Marty knew him in the future and had to catch up Doc’s memory with the futuristic tech he came in. Some diagetic sound I heard was the TV static around the beginning of the clip. While Marty was adjusting the screen to show Doc a video from the future, the TV was staticky and mixed in with the character’s voices. A nondiagetic sound would be the music that began to play at around the two and half minute mark. It’s just there for the viewer to hear and the emotion of music often matches the emotion of the characters.