Blow Out(1981)

When audio technician Jack Terri is recording sound effects for a movie, he hears a car crash. Just as the car is sinking in the river, Jack pulls the woman inside to safety, but cannot save the other passenger. When he learns that man who drowned was a presidential candidate, he suspects that the wreck was not an accident, but murder. After Jack becomes romantically involved with the woman he saved, he learns that she is part of a scheme to blackmail important men, and he begins to wonder if things are as they appear to be. Jack realizes that he was right about the "accident" when the assassin focuses on him and his girlfriend, and he has to utilize all of his special effects skills to keep them alive.