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Category: Visual and Media Accessibility

Time-based Media Alternatives

Also known as: Alternative for Time-based Media, Media Alternative
Simply put

A time-based media alternative is a text-based document that describes what happens in audio or video content, so that people who cannot hear or see the media can still get the same information. It provides a running account of the dialogue, sounds, and visual events in the media. This helps make prerecorded audio and video content perceivable to a wider range of users.

Formal definition

Under WCAG Guideline 1.2 (Time-based Media), an alternative for time-based media is a text-based (though not necessarily text-only) document that provides a running description of all information in synchronized media, presenting equivalent information for audio, video, or audio-video content. It is the mechanism referenced in success criteria such as 1.2.8 Media Alternative (Prerecorded), which is a Level AAA criterion in WCAG 2.1 that also applies to video-only media, as well as Level A provisions for prerecorded audio-only and video-only content under 1.2.1. The alternative should convey dialogue, non-speech audio cues, and visual events in a form accessible to users who cannot access the original media. Note that specific success criteria and their conformance levels differ across WCAG versions, and conformance with these criteria supports but does not by itself guarantee an accessible experience; manual and assistive technology testing remain necessary. This entry is informational and not legal advice.

Why it matters

Audio and video content can present significant barriers for people who cannot hear or see the media. A person who is deaf or hard of hearing may miss spoken dialogue and important non-speech sounds, while a person who is blind or has low vision may miss visual events that carry meaning. Someone who is deafblind may be unable to access either channel. A time-based media alternative addresses these gaps by providing a running, text-based account of what happens in the media, so that the same information can be reached in a form the user can perceive and, when needed, render through assistive technology such as a screen reader or refreshable braille display.

Providing a media alternative also supports flexibility beyond a single group of users. Because the alternative is text-based, it can be read at the user's own pace, translated, searched, or referenced without playback, which benefits people in situations where playing audio or video is impractical. For content owners, offering equivalent information helps make prerecorded material perceivable to a wider audience and supports conformance with WCAG Guideline 1.2.

It is important to keep expectations realistic. Meeting a WCAG success criterion related to media alternatives supports accessibility but does not by itself guarantee an accessible experience for every user, and it does not guarantee legal compliance. Automated tools cannot fully verify whether an alternative conveys equivalent information; manual review and assistive technology testing remain necessary. This entry is informational and not legal advice, and readers should consult qualified counsel regarding specific obligations.

Who it's relevant to

Content creators and video producers
Teams producing prerecorded audio, video, or synchronized media are responsible for supplying an alternative that conveys dialogue, meaningful sounds, and visual events. Building this into the production workflow makes it easier to present equivalent information rather than retrofitting it later.
Accessibility engineers and QA testers
Those verifying WCAG conformance need to confirm that a media alternative actually presents equivalent information, not just a partial transcript. Because automated checks cannot fully evaluate equivalence, manual review and assistive technology testing are required to confirm the alternative works as intended.
UX designers and content strategists
Designers decide how the text-based alternative is presented and located so users can find and use it. Because the alternative is text-based, it can also be read at the user's pace, searched, or referenced without playback, which informs how it is surfaced in the interface.
Compliance officers and legal counsel
Those assessing organizational obligations should understand where media alternatives fit within WCAG Guideline 1.2 and the differing conformance levels across versions. Conformance supports accessibility goals but does not by itself guarantee legal compliance; specific requirements evolve through regulation and case law and warrant review with qualified counsel.

Inside Time-based Media Alternatives

Time-based Media
Content that presents information over time, including audio-only, video-only, audio-video, and combinations of these with interactive components. WCAG uses this category to group media whose content unfolds temporally rather than statically.
Text Transcript
A text-based equivalent of the audio and, where applicable, visual content of time-based media. Transcripts support users who are deaf, hard of hearing, or who cannot process audio, and can also aid users of assistive technology and those in low-audio environments.
Captions
Synchronized text representing spoken dialogue and important non-speech audio (such as sound effects and speaker identification). WCAG addresses captions for prerecorded content and, at higher conformance levels, for live content.
Audio Description
Narration added to describe important visual information not conveyed through the main audio track, benefiting users who are blind or have low vision. WCAG includes success criteria for audio description of prerecorded synchronized media.
Sign Language Interpretation
Interpretation of audio content into sign language, addressed at the WCAG AAA level for prerecorded synchronized media rather than at AA.
Media Alternative (Full Text Alternative)
A time-synchronized or document-based text alternative that conveys equivalent information to the media, used to satisfy certain success criteria depending on whether the media is a media alternative for text or standalone content.

Common questions

Answers to the questions practitioners most commonly ask about Time-based Media Alternatives.

Do captions and a transcript together satisfy every WCAG requirement for a video?
Not necessarily. Captions address the audio content for people who are deaf or hard of hearing, but WCAG also addresses visual information conveyed in the video through audio description or a media alternative for time-based media. For prerecorded video that contains meaningful visual content not otherwise available in the audio track, WCAG 1.2.5 (Audio Description, Level AA) commonly applies, and a text transcript alone may not cover the synchronized nature of the content. The specific requirements depend on the media type (audio-only, video-only, or synchronized) and the conformance level being targeted. Meeting these success criteria supports accessibility but does not by itself guarantee an accessible experience for all users or legal compliance; manual review and testing with assistive technology are generally also needed.
Is a text transcript always an acceptable substitute for captions?
Generally no, at least not for synchronized media at the AA level. A transcript can serve as an alternative for audio-only or video-only content, and WCAG 1.2.1 (Level A) addresses those cases. However, for synchronized media, captions are commonly required under WCAG 1.2.2 (Captions, Level A) because they present content in time with the audio, which supports users who rely on the visual context and timing. A transcript is often a valuable supplement but does not, on its own, replace synchronized captions for most video-with-audio content. The applicable requirement depends on the media type and the conformance level you are targeting.
How do I decide whether a video needs audio description?
Consider whether important visual information is presented that is not already conveyed in the existing audio track. If the narration or dialogue already describes what is shown, additional audio description may not be needed. If meaningful visual content (on-screen text, actions, charts, or scene changes) is not otherwise available to someone who cannot see the screen, audio description or a media alternative is commonly indicated. WCAG addresses this through criteria such as 1.2.3 (Level A) and 1.2.5 (Level AA). A practical step is to review the video with the visuals hidden and note what information is lost.
Can automated tools verify that time-based media alternatives are adequate?
Only to a limited degree. Automated testing can flag the absence of a caption track or a transcript link, but it generally cannot assess whether captions are accurate, properly synchronized, or complete, or whether audio description conveys the necessary visual information. Evaluating the quality and accuracy of these alternatives typically requires manual review, including watching or listening to the content and, where relevant, testing with assistive technology. Automated checks detect only a portion of potential issues.
What is the difference between open captions and closed captions, and when should I use each?
Closed captions can be toggled on or off by the user and are commonly delivered through a separate track that the media player renders. Open captions are permanently rendered into the video image and cannot be turned off. Closed captions are often preferred because they give users control and can support multiple languages, but open captions may be used where the delivery platform does not reliably support a caption track. Either approach can support the intent of WCAG caption criteria; the choice often depends on the platform, distribution method, and user needs.
How can I provide audio description when re-recording a narration is not feasible?
One commonly used approach is to author the video so there are natural pauses long enough to insert descriptions of key visual content, allowing standard audio description to fit within the existing timeline. Where that is not possible, an extended audio description (which pauses the video to allow longer descriptions) or a full media alternative for time-based media, a text document combining dialogue and descriptions of visual content in sequence, may serve the purpose. The appropriate option depends on the content and the conformance level you are targeting; planning for description needs during production generally reduces later rework.

Common misconceptions

Automatically generated captions are sufficient to meet accessibility requirements.
Auto-generated captions frequently contain errors in wording, punctuation, speaker identification, and non-speech audio. Meeting WCAG expectations generally requires captions that accurately represent the audio, which typically means human review or correction. Automated tools detect and produce only a portion of what is needed, and manual verification is commonly required.
A transcript alone satisfies all time-based media requirements.
A transcript may address some criteria, but synchronized media generally also requires captions and, for visual content, audio description. The appropriate alternatives depend on the media type and the targeted WCAG version and conformance level; a transcript does not by itself cover synchronized visual information for sighted needs or timing needs met by captions.
Providing media alternatives guarantees legal compliance.
Conformance with specific WCAG success criteria is distinct from legal compliance and from real-world usability. WCAG is a technical standard published by the W3C, while obligations under laws such as the ADA are shaped by regulation, agency guidance, and case law. Meeting criteria does not guarantee an accessible experience for every user or immunity from claims; consult qualified legal counsel for jurisdiction-specific questions.

Best practices

Identify the media type (audio-only, video-only, or synchronized audio-video) first, then determine which alternatives apply, since captions, audio description, and transcripts serve different needs.
Provide accurate, human-reviewed captions rather than relying solely on auto-generated output, ensuring they include speaker identification and important non-speech audio.
Include audio description for significant visual information in synchronized media that is not otherwise conveyed through the main audio track.
Offer a complete text transcript for time-based media to support users who cannot access audio or video and to provide a searchable, navigable alternative.
Confirm which WCAG version and conformance level you are targeting, noting that some alternatives such as sign language interpretation are addressed at the AAA level rather than AA.
Verify alternatives through manual and assistive technology testing in addition to automated checks, since automated testing detects only a portion of media accessibility issues.