Subtitles are text derived from either a transcript or screenplay of the dialog or commentary in films, television programs, video games, and the like, usually displayed at the bottom of the screen, but can also be at the top of the screen if there is already text 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 to help viewers who are deaf or hard of hearing to follow the dialog, or people who cannot understand the spoken dialogue or who have accent recognition problems.

The encoded method can either be pre-rendered with the video or separate as either a graphic or text to be rendered and overlaid by the receiver. The separate subtitles are used for DVD, Blu-ray and television teletext/Digital Video Broadcasting (DVB) subtitling or EIA-608 captioning, which are hidden unless requested by the viewer from a menu or remote controller key or by selecting the relevant page or service (e.g., p. 888 or CC1), always carry additional sound representations for deaf and hard of hearing viewers. Teletext subtitle language follows the original audio, except in multi-lingual countries where the broadcaster may provide subtitles in additional languages on other teletext pages. EIA-608 captions are similar, except that North American Spanish stations may provide captioning in Spanish on CC3. DVD and Blu-ray only differ in using run-length encoded graphics instead of text, as well as some HD DVB broadcasts.

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. Television subtitling for the deaf and hard of hearing is also referred to as closed captioning in some countries.

More exceptional uses also include operas, such as Verdi's Aida, where sung lyrics in Italian are subtitled in English or in another local language outside the stage area on luminous screens for the audience to follow the storyline, or on a screen attached to the back of the chairs in front of the audience.

The word subtitle is the prefix sub- ("below") followed by title. In some cases, such as live opera, the dialog is displayed above the stage in what are referred to as surtitles (sur- meaning "above").

Tools

We have written and collected some software that can be used for the pre- and post-processing of ASR. The description of the software and the possibility to download, can be found in the Software developed by our team (left).