Open captions are captions that are permanently rendered into the video picture, so every viewer sees them and nobody can turn them off. In video accessibility, open captions provide a text version of dialogue and meaningful sounds for deaf and hard-of-hearing viewers, and because they are part of the image, they work on any screen and in any player.
The defining feature is where the text lives. Closed captions travel as a separate data track that the player renders on request, while open captions are burned in during rendering or encoding. That difference decides how flexible, searchable and adjustable the captions are.
How open captions are produced
Open captions begin as an ordinary timed caption file, such as SRT, WebVTT or SCC, or as captions authored directly in an editing timeline. At export, the editing or encoding software draws the text onto each frame at the given timecodes, so the result is a single video stream with the captions inside the pixels.
Because the text becomes image content, every typographic choice is fixed at render time: font, size, color, background box, position and line breaks. This gives the producer complete control over appearance but removes all control from the viewer.
| Step | Task | Quality check |
|---|---|---|
| Transcription | Accurate text of speech and sounds | Verbatim accuracy, speaker changes |
| Segmentation | Split text into caption events | Natural phrase breaks, two lines maximum |
| Timing | Set in and out points | Synchronized with speech and shot changes |
| Styling | Font, size, box, safe area | Legible on smallest target screen |
| Burn-in | Render text into frames | Review full export before delivery |
Caption content and style parameters
Good open captions follow the same content rules as closed captions: they reproduce dialogue, identify speakers when this is not obvious and describe relevant non-speech sounds such as music, laughter or a door slamming. Captions that omit sound cues are effectively subtitles.
Readability depends on line length, reading speed and contrast. The values below are common working ranges in professional captioning guidelines; individual broadcasters and platforms set their own exact limits.
| Parameter | Common range | Effect |
|---|---|---|
| Lines per caption | 1 to 2, rarely 3 | Limits how much of the picture is covered |
| Characters per line | About 32 to 42 | Short lines read faster on small screens |
| Reading speed | About 15 to 20 characters per second | Too fast and viewers miss text |
| Minimum duration | About 1 to 1.5 seconds | Short events become unreadable |
| Contrast | Light text on a dark box or outline | Legible over bright or busy images |
| Position | Lower third within the title safe area | Moved up to avoid on-screen text |
Because the viewer cannot resize burned-in text, size must suit the smallest likely screen. Text that is comfortable on a television can become illegible on a phone in a social feed, so many producers design open captions primarily for mobile viewing.
Open captions compared with closed captions and subtitles
Open captions, closed captions and subtitles overlap but serve different audiences and delivery paths. Captions assume the viewer cannot hear the audio, while subtitles usually assume the viewer can hear but does not understand the language.
| Format | Visibility | Content | Viewer control |
|---|---|---|---|
| Open captions | Always on, part of the image | Dialogue plus sound cues | None |
| Closed captions | On request, separate track | Dialogue plus sound cues | On or off, often style and size |
| Subtitles | Usually on request | Translated dialogue | Language selection |
| Burned-in subtitles | Always on, part of the image | Translated dialogue only | None |
Closed captions are generally the preferred accessibility solution where the platform supports them, because viewers can adjust them and search engines and assistive tools can read the text. Open captions win when caption support is absent or unreliable.
When to choose open captions
The decision depends on the distribution channel, the audience and the need for flexibility. Many productions deliver both: an open-captioned version for specific outlets and a clean version with a closed caption file for everything else.
| Situation | Recommended choice | Reason |
|---|---|---|
| Social feeds with autoplay muted | Open captions | Text shows even without caption settings |
| Public screens and kiosks | Open captions | No player controls available |
| Cinema accessibility screenings | Open captions | Whole audience sees the same print |
| Streaming and broadcast | Closed captions | Viewer choice and regulatory formats |
| Multilingual distribution | Closed captions or subtitles | One master serves many languages |
Accessibility requirements and pitfalls
Accessibility guidelines such as WCAG 2.2 require captions for prerecorded video with audio at Level A and for live video at Level AA. Open captions can satisfy these requirements when they are accurate, complete and synchronized, but they bring specific risks.
- Errors are permanent; fixing a typo requires a new render and redistribution.
- Text cannot be resized or restyled, which disadvantages viewers with low vision.
- Captions can cover important picture content such as lower thirds or on-screen graphics.
- Re-encoding and scaling can blur thin fonts, so outlines or boxes are safer than plain text.
- Burned-in text is not searchable unless a separate transcript or caption file is also provided.
In plain words
Open captions are words printed directly onto the video, like text painted on a poster. Everyone who watches sees them, and there is no button to hide them.
This makes them reliable: they appear on any screen, even where captions cannot be switched on. The trade-off is that viewers cannot make the text bigger, change its color or turn it off.
A real-world example
A city transport authority produces short safety videos that play on screens in stations and on its social media accounts. Station screens have no audio and no caption controls, and most social viewers scroll with sound off.
The video editor creates an accurate caption file with sound cues such as [train approaching] and burns it in using a sans serif font on a semi-transparent black box, limited to two lines of about 32 characters and placed above the station screens’ ticker area. For the website, the team uploads a clean version with a separate closed caption file so that viewers can resize the text.
The result is that every passenger can follow the safety message without sound, and the authority meets its accessibility commitments on all channels.