I believe they are trying to say that they made their movie off of what was only home movies. Because: they had made- they made from what was to have been- from what were strictly home movies- only home movies New sentence: They made from what were only home movies **We changed the "was" to "were" because "was" had "to have been" in front of it so it didn't need to match "home movies" since "have been" matched it however, since I took out the "to have been" the verb became closer to "home movies" and we need to match "home movies" and "was" ***I tried to break it down, just remember that past/present/future perfect can, most of the time, be conjugated in simple past/present/future Hope this helps^^ Have a nice day!

Yuck. Terrible sentence. Okay. There was an hour-long film. They made this film. They had footage that was supposed to be JUST for home movies (aka private movies). They made this film from that footage, and then they showed it to people. Look at the sentence in blocks of words. "[They showed the hour-long film] [they had made from] [what was to have been] [strictly home movies]." The "what was to have been" means "what should have been". In very few words, they made an hour-long public movie out of film footage instead of using it to make private movies.