Glossary
What are closed captions?
By the KeyMo team · Updated
Closed captions are captions a viewer can switch on or off, because the text is stored apart from the picture instead of being part of it. Open captions are part of the video image and always show. For clips posted to social apps, the choice mostly comes down to who controls the look: you or the viewer.
Closed versus open
| Closed captions | Open captions | |
|---|---|---|
| How they are stored | As a separate text track or file | Drawn into the video image |
| Viewer can turn off | Yes, in players that support it | No |
| Who sets the look | The player; W3C notes most web video uses white text in a black box | The editor |
| Typical formats | WebVTT, SRT, TTML | None; they are pixels |
| Editing later | Replace the file | Re-export the video |
W3C's Web Accessibility Initiative puts it plainly: most captions are closed, and open captions are always displayed and cannot be turned off. WCAG 2.2 lists both providing open captions and providing closed captions as sufficient techniques for its prerecorded captions criterion.
Where the term comes from
The FCC describes closed captioning on television as the audio portion of a program displayed as text on screen, for people who are deaf or hard of hearing. Its rules for TV require captions to be accurate, synchronous, complete and properly placed. The FCC's internet page adds a limit worth knowing: its online captioning rules cover programming shown on TV in the U.S. with captions, and consumer-generated media is not required to be captioned unless it was shown on TV with captions. That is a statement of what the FCC page says, not legal advice for your channel.
Caption files and what YouTube does with them
| Format | YouTube's note |
|---|---|
| SubRip (.srt) | Basic version only, plain UTF-8; fine for beginners because it needs only basic timing |
| WebVTT (.vtt) | "In initial implementation"; positioning supported, styling limited to bold, italic and underline |
| TTML (.ttml) | "In partial implementation"; styling and positioning supported |
| SCC (.scc) | Named as YouTube's preferred file when captions are CEA-608 based |
The practical lesson: a clean caption file may lose its styling in a player. If you want a particular look, a file is the weak route. See SRT vs VTT and the glossary entries for SRT file and VTT.
Which to use for clips
- Need the viewer to choose, or need accessibility on a long video: ship a closed caption file as well.
- Need a designed look that survives every app: use open captions, because the style is part of the image.
- Posting the same clip to several apps: open captions behave the same everywhere; closed ones depend on each app's support.
- Not sure: keep an open version for social and a closed-caption file for the full-length original.
Common mistakes
- Treating automatic captions as finished. YouTube says to review and edit them, and W3C says they usually need significant editing to meet accessibility needs.
- Thinking open captions alone fully serve accessibility. WCAG describes captions as covering speaker identity and meaningful sound, not only words.
- Covering the speaker's face or on-screen text. WCAG says captions should not obscure relevant information.
- Assuming one app's menu works like another's. Each app labels its own caption controls.
Where KeyMo fits
KeyMo's captions are open captions. You pick one of 12 styles, or none, and the words become part of each vertical clip. This page does not claim a separate caption-file export. If you need a closed-caption file for the full episode, make one with a captioning tool and keep KeyMo for the short clips. The neighbouring entries on open captions and subtitles cover the other terms.
Sources: Captions/Subtitles, W3C Web Accessibility Initiative (checked 11 October 2026); Web Content Accessibility Guidelines (WCAG) 2.2, W3C (checked 11 October 2026); Closed Captioning on Television, FCC (checked 11 October 2026); Captioning of Internet Video Programming, FCC (checked 11 October 2026); Supported subtitle and closed caption files, YouTube Help (checked 11 October 2026); Use automatic captioning, YouTube Help (checked 11 October 2026).