WebVTT is a time-aligned text format for HTML media. For video accessibility, use it to provide an accurate, clearly labeled caption track that includes dialogue and meaningful non-speech audio—not just a transcript of spoken words. Adding a valid .vtt file is only one part of the work: its text must match the audio, its cues must appear at the right moments, and the player must let viewers find and use the track.
What WebVTT does
WebVTT (Web Video Text Tracks) is an external text format for timed cues associated with HTML audio or video. The W3C specification covers captions, subtitles, chapters and other metadata uses; for accessibility work, its most familiar role is supplying captions or subtitles. A WebVTT file does not create a transcript or captions automatically. It stores text and timing that a media player can present alongside the video. W3C’s WebVTT specification describes the format and its cue types.
WebVTT is not itself a guarantee of accessible media. The words, timing, track labeling, visual presentation and playback controls all affect whether viewers can use the captions.
Captions and subtitles are not quite the same
Terminology varies by region, so track purpose and language labels matter more than relying on the word “captions” or “subtitles” alone.
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- Captions communicate dialogue and meaningful audio information, such as a sound effect, music cue or speaker change. They are intended to help people who are deaf or hard of hearing follow the audio content.
- Subtitles commonly render dialogue in another language and may not include non-speech sounds. A translation-only track should not be assumed to provide the same information as captions.
W3C’s Web Accessibility Initiative (WAI) describes WebVTT as the most common web caption format and also names SRT and TTML as alternatives. Which format to use depends on whether the target player accepts it and supports the features your captions need; the format name alone does not establish compatibility. WAI’s captions and subtitles guidance explains the distinction and discusses caption creation.
How to add a WebVTT captions track to HTML video
Place a <track> element inside the <video> element. Set kind="captions", point src to the WebVTT file, identify the track language with srclang, and give viewers a readable label.
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<video controls>
<source src="lesson.mp4" type="video/mp4">
<track kind="captions" src="lesson-en.vtt" srclang="en" label="English">
</video>This follows the pattern in WAI’s H95 technique for using the track element, which recommends checking that the video has a captions track in the language used in the video. For another language, use the appropriate language code and a label that makes the track’s language and purpose understandable. If you offer several tracks, label each so viewers can distinguish them.
The markup only connects a file to the media. It does not verify the caption text, guarantee that the file can be loaded by a particular player, or make an inaccessible player accessible. Check the deployed video and controls as well as the source.
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What a WebVTT file looks like
A basic file begins with the WEBVTT header. Each cue has a start and end time separated by -->, followed by the text to show during that interval. This example illustrates a speaker annotation and a sound cue:
WEBVTT
00:00:01.000 --> 00:00:03.000
<v Narrator>Welcome to the lesson.
00:00:03.500 --> 00:00:05.000
[door closes]The voice annotation identifies the speaker. The bracketed sound description is an editorial example, not a mandatory notation: the goal is to convey relevant audio information clearly. The specification defines WebVTT syntax and cue behavior; consult it when creating more complex tracks or using styling. W3C WebVTT specification.
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Make captions accurate, timed and readable
Automatic captions can be a starting point, but WAI advises editing them for accuracy. Review the captions against the actual media rather than treating an automatically generated transcript as finished.
- Check the words against the audio. Correct misheard speech, names and other errors that change meaning.
- Include meaningful audio beyond dialogue. Add relevant sound effects, music cues or other audio information needed to understand what is happening. Identify speakers when doing so helps viewers follow the exchange.
- Review timing and line breaks while watching. Cues should correspond to the moment their audio occurs, and segmentation should be easy to follow. The cited WAI guidance does not establish a numeric reading-speed, timing or line-length threshold, so do not treat an unsupported number as a universal rule.
- Check the track in the player. Confirm the captions option is available, the language and label are clear, and the displayed text stays readable during playback.
- Consider contrast and placement. Video imagery changes from scene to scene, so text that looks clear over one frame may disappear over another. W3C’s WebVTT guidance calls attention to text and background as well as the video’s colors; avoid styling that makes captions hard to read or hides important visual content.
Caption editing software or a captioning service can help with production, but neither removes the need to review the finished track in context. WAI specifically advises editing automatic captions for accuracy. WAI captions/subtitles guidance.
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What captions do not provide by themselves
Captions convey audio information. They cannot explain a chart, action or other important visual detail that is not spoken aloud. Depending on the video, viewers may also need audio description or another form of visual description, a descriptive transcript, sign language, or an accessible player. A descriptive transcript can combine dialogue and other audio text with descriptions of visual information. WAI’s overview of accessible audio and video covers these complementary approaches.
Choose the additional format based on what the video communicates visually and who needs access to it. Captions are an important part of an accessible video, not a substitute for every other access feature.
Choosing a caption file format
WebVTT is a common choice for web captions, but SRT and TTML are also used. The available guidance does not establish platform-by-platform compatibility or a feature ranking among them. Before choosing, check the target player’s accepted formats, the caption or subtitle features your project needs, and how your workflow will support editing and translation. Whichever format you use, make sure the delivered track is correctly labeled and usable in the player. WAI’s format guidance names these alternatives; WAI H95 demonstrates the HTML track connection.
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