This is very very old, probably from the '80s, if not before. I happened to watch it several years ago and it is extremely probable it is a telefilm, part of some sort of series.
Unfortunately, only few details remain in my memory.
It is a science fiction - horror setting.
There is a movie crew that is filming a horror movie about an invisible monster that goes around killing people.
So, they are going to film a scene in a bedroom with an actor, and they tell him to lay in the bed, and after some time struggle a bit in a frantic way, and then lay still (all alone, since the monster is invisible, so the actor must fake the aggression).
Obviously (for us right now), when they check the actor, after the filming, they discover he is really dead, probably strangled but I don't remember.
Afterwards, they review the movie, I think on cinema screen and not on a monitor, and they see some strange white shadows hovering on the actor at the time of the attack.
Suddenly, while they are surprised, all the members of the crew die one by one, and the final scene is the cinema screen totally white with a shadow on it of some humanoid monster.
I think they called the monster a generic name, like the being, or the creature, or the thing.