Subtitles or captioning are textual versions of the dialog in films and television programs, usually displayed at the bottom of the screen. They can either be a form of written translation of a dialog in a foreign language, or a written rendering of the dialog in the same language—with or without added information intended to help viewers who are deaf and hard-of-hearing to follow the dialog. Sometimes, mainly at film festivals, subtitles may be shown on a separate display below the screen, thus saving the film-maker from creating a subtitled copy for perhaps just one showing. In the United States, television subtitling for the deaf and hard-of-hearing is closed captioning.
Today professional subtitlers usually work with specialized computer software and hardware where the video is digitally stored on a hard disk, making each individual frame instantly accessible. Besides creating the subtitles, the subtitler usually also tells the computer software the exact positions where each subtitle should appear and disappear. For cinema film, this task is traditionally done by separate technicians. The end result is a subtitle file containing the actual subtitles as well as position markers indicating where each subtitle should appear and disappear. These markers are usually based on timecode if it is a work for electronic media (e.g. TV, video, DVD), or on film length (measured in feet and frames) if the subtitles are to be used for traditional cinema film.
The finished subtitle file is used to add the subtitles to the picture, either directly into the picture (open subtitles); embedded in the vertical interval and later superimposed on the picture by the end user with the help of an external decoder or a decoder built into the TV (closed subtitles on TV or video); or converted to tiff or bmp graphics that are later superimposed on the picture by the end user (closed subtitles on DVD).
Subtitles can also be created by individuals using freely-available subtitle-creation software like Aegisub and then hardcode them onto a video file with programs such as VirtualDub in combination with VSFilter which could also be used to show subtitles as softsubs in many software video players.