Captions on Website Video: Who Uses Them and What WCAG Asks
A service video without captions loses more viewers than most businesses expect. Here is what WCAG requires, what the research on captions shows, and how to add a captions track that browsers and players can actually use.
Many business websites now carry at least one video: a founder explaining the service, a short walkthrough of a process, or a client testimonial. Those videos are usually planned around the picture. The sound, which holds most of the message, is treated as something every viewer will hear. Plenty of viewers won’t. Some are deaf or hard of hearing, some are reading a page in a second language, and some are watching on a phone in a quiet office with the sound off.
Captions are synchronized text that carries a video’s speech and its meaningful non-speech sounds. This article sets the Web Content Accessibility Guidelines (WCAG) beside a research review on how captions affect comprehension, a large UK audience survey, and browser documentation from MDN, to explain who captions serve, what the standard asks for, and what a working setup looks like.
Who a missing caption actually excludes
The obvious audience is people who are deaf or hard of hearing, and for them a video without captions is simply a video without its audio. WCAG states the purpose of its captions requirement in exactly those terms: to let people who are deaf or hard of hearing follow synchronized media.
The audience turns out to be much wider. In 2006 Ofcom, the UK communications regulator, published research for its review of television access services. It estimated that over 7.5 million UK adults, about 18% of the adult population, had used subtitles at least once, and that over 6 million of them had no hearing impairment.
Research on comprehension points in the same direction. In a 2015 review in Policy Insights from the Behavioral and Brain Sciences, Morton Ann Gernsbacher of the University of Wisconsin–Madison brought together evidence from deaf education, second-language learning, adult literacy, and reading research. She reports that more than 100 empirical studies show captions improve comprehension of, attention to, and memory for video. The benefit is strongest for people watching in a non-native language, people learning to read, and people who are deaf or hard of hearing, but the review finds it extends to highly literate, hearing adults as well.
What goes wrong without them
- The message lives only in the sound. A testimonial or a “how we work” video is mostly speech, so a viewer without audio sees faces and stock footage but gets none of the content.
- Second-language visitors fall behind. A service business serving a mixed-language area loses the viewers who would follow written English more easily than spoken English.
- Muted viewing becomes a dead end. Without an earlier click or tap on the site, browsers generally let a video start on its own only when it is muted, so a video that autoplays often begins without sound, the condition in which captions matter most.
What WCAG asks for
WCAG groups its video requirements under Guideline 1.2, Time-based Media. The success criteria most relevant to a typical business site are these:
| Success criterion | Level | What it requires |
|---|---|---|
| 1.2.1 Audio-only and Video-only (Prerecorded) | A | A text alternative for audio-only content, and a text or audio alternative for video with no sound |
| 1.2.2 Captions (Prerecorded) | A | Captions for all prerecorded audio in synchronized media |
| 1.2.3 Audio Description or Media Alternative (Prerecorded) | A | A description of important visual information, or a full text alternative |
| 1.2.4 Captions (Live) | AA | Captions for live audio, such as a streamed event |
| 1.2.5 Audio Description (Prerecorded) | AA | Audio description of important visual information |
The W3C’s Understanding document for 1.2.2 clarifies what counts. Captions include dialogue, but they also identify who is speaking and carry meaningful sounds, such as music or a sound effect the story depends on. Leaving out some dialogue or an important sound effect is listed as a failure of the criterion (failure F8).
There is one narrow exception. Captions are not needed when the video is a media alternative for text: it presents no more information than the text already on the page, and it is clearly labeled as such. A spoken version of a written process description can qualify. A testimonial with new information usually does not.
How captions work in the browser
On a site that hosts its own video, the HTML <track> element attaches timed text to a <video> element. The text lives in a separate WebVTT file (.vtt), a plain-text format of timestamps and cue lines.
<video controls playsinline poster="/media/process-poster.jpg">
<source src="/media/our-process.mp4" type="video/mp4" />
<track default kind="captions" srclang="en" label="English" src="/media/our-process.en.vtt" />
</video>Three details in that markup matter more than they look.
- The
kindvalue. MDN’s reference distinguishescaptions, meant for when sound is unavailable or not clearly audible and including sound effects and other relevant audio, fromsubtitles, meant for when the sound is heard but not understood. Ifkindis left out, the browser treats the track as subtitles. - The
defaultattribute. It enables the track unless the viewer’s own preferences point to a more suitable one. Only one track per video may carry it. - The file’s origin. MDN notes that the
.vttfile must come from the same origin as the page unless the video element sets acrossoriginattribute. A captions file on a separate media domain can fail to load without any visible error.
A third-party player such as YouTube or Vimeo handles the track for you, but the captions still have to be written or reviewed. WCAG’s sufficient techniques accept either closed captions, which the viewer can switch on and off, or open captions burned into the picture. Closed captions are usually the better choice, because viewers who do not need them can turn them off, and many players let viewers change their size or style.
“If the sound carries the message, the captions are the message for anyone who can’t hear it.”
— Windware Studio Practice Note
Autoplay and the muted hero video
Background video in a homepage hero is a different case. MDN’s autoplay guide explains that browsers generally block autoplay for media with audible sound, while muted media or media with no audio track is not affected. That is why most hero videos are muted loops with no meaningful audio.
A silent, decorative loop does not need captions, because there is no audio to caption. It still falls under another rule: WCAG 2.2.2, Pause, Stop, Hide (Level A), requires a way to pause, stop, or hide moving content that starts automatically, lasts more than five seconds, and is shown alongside other content. A visible pause control meets that need.
Limits and tradeoffs
Automatic captions are tempting, and they are improving, but they are not yet a finished product. Gernsbacher’s 2015 review noted that captions from automated speech recognition were “not yet without interfering error.” YouTube’s own help page still advises creators to add professional captions first and to review automatic ones, because they can misrepresent speech through mispronunciations, accents, dialects, or background noise. For a service business, a misheard price, product name, or legal term is a real cost, so an edit pass is worth budgeting for.
The evidence also has limits worth stating. Ofcom’s figures describe UK television audiences in 2006, not website visitors today, and the research Gernsbacher reviews comes largely from educational and broadcast settings. Together they show that captions serve a broad audience; they do not measure how many visitors to a particular business site watch muted.
Finally, captions solve the sound problem, not the picture problem. A video that shows important information only visually, such as a diagram with no narration, also needs a description or text alternative under criteria 1.2.1, 1.2.3, and 1.2.5.
The studio approach: a captions checklist
Before publishing a video
- Decide whether the video adds information beyond the page text; if it does, it needs captions.
- Start from a transcript or automatic draft, then edit it for names, prices, and terms.
- Include speaker names when it is not obvious who is talking, and note meaningful sounds.
- Publish the full transcript on the page as well, which also helps visitors who prefer to read.
When building the player
- Use
<track kind="captions">withsrclangand a readablelabel, not the defaultsubtitleskind. - Serve the
.vttfile from the same origin, or setcrossoriginon the video. - Keep player controls visible so viewers can switch captions on and resize them.
- Give any autoplaying, muted background video a visible pause control.
- Watch the published video once with the sound off, start to finish.
Practical takeaways for your next website
- Caption every prerecorded video that speaks; WCAG 1.2.2 makes it a Level A requirement.
- Edit automatic captions before publishing; the platforms that generate them recommend it.
- Mark the track as
captions, notsubtitles, so it carries sound cues as well as dialogue. - Treat muted autoplay as the normal case, since browsers mostly block autoplay with sound.
- Add a pause control to moving hero video, and a text alternative where the picture carries the information.
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