영화 필름의 가장자리에 소리를 직접 기록하여 영상과 음향을 동기화하는 방식.
A method of recording sound directly onto a motion picture film strip, ensuring synchronization with the images.
예문:
"The transition from silent movies to SOF technology changed the way stories were told on screen."
"Engineers developed various SOF systems to improve the fidelity of optical soundtracks."