WebVTT captions are timed text stored in a plain-text .vtt file. Each cue has a start time, an end time and text, which a video player can display in sync with playback. In HTML, add the file as a <track> inside a <video> element. WebVTT is a text-track format, not a video format.
What a WebVTT file contains
A WebVTT file begins with the header WEBVTT, followed by cue blocks. A cue associates text with a time range; optional cue settings can affect its presentation. The text may include speaker information or simple emphasis.
WEBVTT
00:00:01.000 --> 00:00:03.000
[Door closes]
00:00:03.200 --> 00:00:05.000
<v Maya>Hello, everyone.The W3C WebVTT specification states: “A WebVTT file must only contain data of one kind, never a mix of different kinds of data.” For example, keep captions and chapters in separate files and tracks rather than combining them in one VTT file. WebVTT can carry captions, subtitles, chapters, audio descriptions or metadata, depending on how the player or HTML track identifies the data. W3C WebVTT specification.
Captions or subtitles: choose by content
The important distinction is what the text communicates, not just the track label. Captions include dialogue and relevant audio information such as sound effects or musical cues. Subtitles commonly provide dialogue only, often as a translation for viewers who can hear the audio. Terminology varies by region.
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If a sound matters to understanding the video, include it in the text. For instance, a meaningful door slam could be represented as [Door closes]; dialogue alone would not convey that event. W3C WAI notes that a track labeled “subtitles” can still meet a caption criterion in some cases if it includes relevant audio information. Its HTML technique is one documented way to meet WCAG, not a mandatory implementation method. W3C WAI technique H95.
Add an external VTT file to an HTML video
First save the VTT file somewhere the page can load, then add a <track> element inside the <video> element:
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<video controls>
<source src="/media/lesson.mp4" type="video/mp4">
<track
kind="captions"
src="/media/lesson.en.vtt"
srclang="en"
label="English captions"
default>
</video>kind="captions"identifies a track intended as captions. Choose the track kind that matches its content.srcis the path to the VTT file. It must resolve correctly from the page where the video is embedded.srclangidentifies the track language, using a language code such asen.labelprovides a user-facing name for the track, such as “English captions.”defaultmarks a preferred track when user preferences do not select a better match. Use it on no more than one track per video.
For another language, add another track with its own VTT file, language code and clear label. MDN documents WebVTT as the format for HTML text tracks. MDN: The <track> element.
Author cues in a file or create them with JavaScript
External VTT file
A plain-text VTT file is the direct option for most pages: write the header and cues, host the file, and reference it with <track>. It is easy to review independently of the page and to maintain as a separate asset.
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JavaScript text tracks
Developers can also create a text track in JavaScript, set its mode and add VTTCue objects. This can be useful when cues need to be generated or managed dynamically, but it requires code to construct and maintain the timing and text. MDN documents the TextTrack and cue APIs. MDN: TextTrack.
Styling cue text
The CSS ::cue pseudo-element can style cue text. Do not rely on ::cue-region for region-specific styling: MDN reports that browsers do not support it. Check the target browsers and player rather than assuming every styling behavior is available. MDN: ::cue.
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Check the captions before publishing
- Validate the file structure. Confirm the first line is
WEBVTTand that each cue has a valid start and end time. - Check the file path. Load the page and verify the video can retrieve the VTT file at the
srcURL. - Review language and label. Make sure
srclangidentifies the cue language and the label clearly tells viewers what they are selecting. - Watch the video with the track enabled. Check synchronization, spelling, speaker identification and relevant non-speech audio.
- Test the actual player. Confirm track selection and default behavior in the browser and player you intend to use. HTML documentation describes the element, but behavior should be verified in your own target setup.
- Keep each file to one data kind. Use separate files and tracks for other languages or kinds of text data.
Optional metadata guidance for archives and collections
For archival or collection workflows, the Federal Agencies Digital Guidelines Initiative (FADGI) lists version 2.0 of its Guidelines: Embedded Metadata in WebVTT Files, dated September 1, 2026. The guidance addresses provenance, administrative history and context for WebVTT captions, subtitles and descriptive audio. Metadata can help users and collection administrators understand the data kind, origin, and when, where and how it was made. This is specialized collection guidance, not a universal requirement for a standard web caption track. FADGI: Guidelines for Embedded Metadata in WebVTT Files.
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