"Film at 11" is an idiom from television news broadcasting, where the viewer is informed that footage of a breaking news story will be screened later that evening. 11 o'clock is the traditional timeslot for late evening local news broadcasts in the Eastern and Pacific time zones of the United States. Television news gathering originally involved crews using 16 mm film which would be processed at the station, and had to be edited before it could be aired. The time taken for this process meant that the pictures of an early evening event would only be available in time for the late newscast.
The purpose of these "Film at 11" promotions was usually to oversensationalize the story so that a fearful public would tune in and increase the program's ratings. This is a later interpretation of the idiom, as news broadcasts were not counted in ratings during the time 16mm film was used in newsgathering and hence promotions typically took the form of "newsflashes" or "special reports" which simply conveyed the facts of the story.
The phrase itself became obsolete with the advent of videotape as the medium of choice for news reporting.
The phrase entered popular culture in the 1970s, often describing ordinary or mundane events with an implication that said events were being overly sensationalized.
The phrase is also often used as a short-hand expression akin to "tell you later."