The Social Network is not a 1.78:1 movie, it is 2.35:1 but your TV screen is 1.78:1. This movie will always have black bars top and bottom unless you zoom it with your TV's or player's controls or manually crop it with DVDFab when converting. This means it is 1920x820 or so when decoded and cropped to convert only the active video. Note that when you zoom or crop you are giving up content on each side of the image in exchange for a full screen, a poor tradeoff with many movies.
DVDFab should not encode black bars on the sides, if it is, it is not being cropped correctly.