to be distributed to the audience. Open subtitles are added directly to recorded video frames and thus cannot be removed once added. On the other hand, closed subtitles are stored separately, allowing subtitles in different languages to be used without changing the video itself. In either case, a wide variety of technical approaches and formats are used to encode the subtitles.

Third, subtitles need to be displayed to the audience. Open subtitles are always shown whenever the video is