What is the difference between captions and subtitles?

The two terms describe the same kind of timed text, but they answer different viewers' problems. The web standard puts the line there. Subtitles are a transcription or translation of the dialogue, for when the sound is available but not understood ¹. Captions cover more: a transcription or translation of the dialogue, sound effects, relevant musical cues and other relevant audio information ².

So a French film with English subtitles helps an English speaker who can hear the French follow the story. A deaf viewer of the same film needs captions, which mark a door slam or a song as well as the words.

The viewer's problem decides which one to make

Ask two questions: can the viewer hear the audio, and can the viewer understand the language? The answers point to one file.

A caption file in the video's own language serves the first two rows at once. A translated subtitle file serves the third row, and it does not serve a deaf viewer, because it leaves out the sounds.

Captions carry the rules; subtitles usually do not

The accessibility rules we checked ask for captions. WCAG success criterion 1.2.2 requires captions for prerecorded video, and it is a Level A criterion ³. The FCC's quality standards for televised captions ask that captioning provide non-speech information, such as the identity of speakers, music, sound effects and audience reaction, to the greatest extent possible ⁴. A subtitle track that carries only dialogue does not give that information, so it does not stand in for captions.

Captions for live audio are a separate criterion. WCAG 1.2.4 requires captions for live audio in synchronized media, and it is a Level AA criterion ⁵.

Closed and open versions change who controls the text

The same text can be delivered in two ways. A closed caption is a separate track that the viewer's player shows only when the viewer turns it on ⁶. An open caption is embedded in the picture and is visible to every viewer ⁷. See closed captions and open captions in the glossary.

For a deaf viewer, a closed track lets the viewer choose whether to see it. For a video that must show the text on every screen, such as a social post with no player controls, open captions do that.

It depends: one file can serve both groups

• Same language, mixed audience. A caption file in the video's language serves deaf viewers and anyone watching without sound. You do not need a second file.
• Another language. A translated subtitle file helps hearing viewers who need the language. Deaf viewers of that language still need captions in it, so the two files are separate jobs.
• Live events. The live criterion applies, and automatic live text is a different trade-off from a checked caption file. See live captions.

What to do

1. Name the viewer. Decide whether they cannot hear, cannot understand, or both.
2. Make captions for a deaf or sound-off audience. Use the video's language, add speaker names where the speaker changes, and tag the sounds that matter to the scene.
3. Make subtitles for a language gap. Translate the dialogue. If some viewers also cannot hear, supply captions too.
4. Pick the file type. Use the SRT file for uploads and desktop tools, or WebVTT for a web player. The question what an SRT file is and how it differs from VTT explains the choice.
5. Review any automatic draft. Machine text needs checking against the audio before you publish. See whether automatic captions meet accessibility rules.

For the full checklist, read the guide to captions and subtitles. The subject as a whole is in transcription.