Subtitling is used as a means of translating a medium into another language so that speakers of other languages can enjoy it. In other words, subtitles are translations for people who don’t speak the language of the medium.
Subtitled foreign films are a good example: without subtitles, English-speaking audiences would be unable to follow the plot of a French or Spanish movie. Subtitles are best-suited and most often used for pre-recorded videos, such as movies, TV shows, and employee training videos, etc.
Captioning, on the other hand, is more commonly used as a service to aid deaf and hearing-impaired audiences. They are more adaptable to live broadcasts, such as news broadcasts, sporting events, and live TV shows.
Captions are a text version of the spoken part of the medium. They are in the language of the medium rather than a translation to another language. They can either be open or closed; closed captions can be turned on or off whereas open captions are part of the video itself and cannot be turned off.
Usually, captions appear as white text within a black box, appearing a second or two after the spoken words.