In silent movies, when the actors portray a dialog, you can see their mouths move – but of course you can’t hear what they say. Are these just random mouth movements? Do they actually follow a script that’s related to the movie’s plot? Or are they chit-chatting with each other on some unrelated subject? My lip-reading skills are apparently not good enough.
Related question: Is there a name for the “slides” shown at various intervals in a slient movie to tell the audience what’s happening onscreen at the moment?
Depended entriely on the director. Some were very strict and the actors worked from a script (some perfoemrs even prided themselves on speaking, French, say, if they were playing a Frenchperson).
Other directors gave the cast an overview of what sort of things will be said or are happening, and the dialogue was improvised.
But no one used “random mouth movements,” and anyone who cursed or gossiped got tons of irate (or amused) mail from lip-readers.
The titles are usually called “subtitles,” though the technically correct term is “intertitles.”