I wouldn't use "ablaufen" for a film, except in a very technical sense.
Most of the time, it's just "laufen":
Läuft der Film schon? (In both senses: Läuft der Film schon in den Kinos in Deutschland? Läuft die Verstellung um 19:30 h schon?)
Der Film "Metropolis" läuft mittwochs um 19:30 h im Metropol-Kino.
Bitte lassen Sie Ihre Handys aus, während der Film läuft.
You can use "ablaufen" in a narrow mechanical sense with actual film, saying that it is being spooled off from one reel.
Der Film läuft von der vorderen Spule ab, läuft durch den Projektor, und wird auf die hintere Spule aufgerollt.
However, you can also just trust in the preposition "von" to convey that:
Der Film läuft von der vorderen Spule durch den Projektor auf die hintere Spule.
"Ablaufen" is also often used in the sense of "to proceed" for events that follow a plan or all kinds of processes, but I wouldn't normally use it in that way for a film:
"Wie läuft der erste Schultag ab?"
Die Hochzeit lief anfangs noch ab wie geplant. Aber dann ...
Your second example is again a technical one, the thread is running off the spool. You can use either "laufen" or "ablaufen" for this. "Ablaufen" just puts a bit more emphasis on the fact that the thread is coming off the spool or that is starts at the spool. Your example sentences both work, and to me there is no semantic difference between them.
There's a lot of other uses of "ablaufen", as you have seen in DWDS.