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Category: Visual and Media Accessibility

Synchronized Media

Also known as: Time-based Media (synchronized), Audio-Video Media
Simply put

Synchronized media is audio or video content that is combined with another format for presenting information, such as captions that appear alongside spoken words or descriptions timed to match what is happening on screen. A common example is a video with speech that includes synchronized captions and, where needed, audio descriptions. Making such content accessible generally means providing alternatives so that people who cannot hear the audio or see the video can still access the information.

Formal definition

As defined in the W3C WCAG glossary, synchronized media is audio or video synchronized with another format for presenting information and/or with time-based interactive components. Under WCAG Guideline 1.2 (Time-based Media), synchronized media triggers requirements that vary by success criterion and conformance level, including captions (a synchronized visual and/or text alternative for both speech and non-speech audio information) and audio description for prerecorded video content; for example, Success Criterion 1.2.3 addresses providing either an alternative for time-based media or an audio description for prerecorded synchronized media. Section 508 guidance similarly emphasizes that speech content should have accessible captions synchronized to appear at approximately the same time as the corresponding audio. Practitioners should confirm which specific success criteria and levels (A, AA, AAA) apply to their context, as detailed requirements differ across WCAG versions and criteria; this entry is informational and not legal advice.

Why it matters

Synchronized media, video with sound, audio paired with visuals, or media combined with interactive components, carries information through channels that not every user can perceive. A person who is deaf or hard of hearing cannot access spoken dialogue and meaningful sound without captions, while a person who is blind or has low vision may miss critical visual information that is never spoken aloud. When synchronized media is used for training, marketing, education, government services, or entertainment, failing to provide accessible alternatives can exclude significant audiences from information that others receive automatically.

Under WCAG Guideline 1.2 (Time-based Media), synchronized media triggers a range of requirements that vary by success criterion and conformance level. For example, captions provide a synchronized visual or text alternative for both speech and non-speech audio information, and audio description addresses visual content in prerecorded video. Because AA is the level most commonly cited as a target in accessibility programs and in various settlements and agency guidance, organizations that publish video or audio content should understand which specific criteria and levels apply to their context.

Meeting these criteria is not only a matter of technical conformance but also of usability and, potentially, legal exposure. Providing captions and descriptions helps ensure the underlying information is actually available to people using assistive technology, though conformance alone does not guarantee an accessible experience for every user or immunity from legal claims. Requirements also differ across WCAG versions, so teams should confirm current applicable criteria and consult qualified legal counsel for compliance questions; this entry is informational and not legal advice.

Who it's relevant to

Content and Media Producers
Teams that create video and audio content need to plan for captions and, where required, audio description as part of production workflows. Understanding that captions must convey both speech and non-speech audio information, and appear synchronized with the corresponding audio, helps producers scope this work accurately rather than treating it as an afterthought.
Accessibility Engineers and QA Testers
Practitioners verifying conformance must confirm which specific WCAG success criteria and levels (A, AA, AAA) apply to a given piece of synchronized media, since requirements differ across criteria and WCAG versions. Automated tools detect only a portion of issues, so manual review and assistive technology testing are needed to confirm captions and descriptions actually work for users.
Compliance Officers and Legal Counsel
Those assessing risk should recognize that AA is the level most commonly cited as a target and that Section 508 guidance addresses synchronized captions for federal contexts. Because detailed requirements evolve through WCAG versions, regulation, and case law, and because conformance does not guarantee immunity from claims, organizations should consult qualified legal counsel for jurisdiction-specific questions.
UX Designers and Product Teams
Designers integrating media into interfaces should account for controls to access captions and descriptions and for the possibility of time-based interactive components. Meeting success criteria supports, but does not by itself guarantee, a usable experience for people relying on captions or audio description.

Inside Synchronized Media

Audio Component
The sound portion of the media, which may include spoken dialogue, narration, music, and meaningful sound effects that carry information relevant to understanding the content.
Visual Component
The video or visual portion of the media, presented in a time-based sequence that is coordinated with the audio track.
Time-Based Synchronization
The defining characteristic in which audio and visual elements are presented together in a coordinated timeline, so that what a user sees and hears occurs in the intended relationship.
Captions
A text-based, time-synchronized alternative for the audio content that conveys dialogue and meaningful sounds, commonly used to make audio accessible to users who are deaf or hard of hearing. WCAG addresses captions through success criteria at Level A (prerecorded) and Level AA (live).
Audio Description
Additional narration inserted into pauses in the dialogue to describe important visual information for users who are blind or have low vision. WCAG includes related success criteria for prerecorded synchronized media.
Transcript
A text representation of the media content that may combine both the audio and descriptions of visual information, providing an alternative that can be read or accessed with assistive technology.

Common questions

Answers to the questions practitioners most commonly ask about Synchronized Media.

Do captions and audio descriptions cover the same accessibility need for synchronized media?
No. These address different needs and different audiences. Captions provide a text-based equivalent of the audio track, primarily supporting people who are deaf or hard of hearing by conveying speech, speaker identification, and meaningful sounds. Audio descriptions address the visual channel, providing spoken narration of important visual information for people who are blind or have low vision. Because they serve distinct sensory needs, providing one does not satisfy the requirement for the other. Under WCAG, captions and audio description are covered by separate success criteria, and synchronized media that conveys both meaningful audio and meaningful visual information generally needs to address both.
Is an automatically generated transcript or auto-caption enough to make synchronized media accessible?
Not on its own. Automatically generated captions and transcripts frequently contain errors in wording, punctuation, speaker identification, and timing, and they typically omit non-speech sounds that may be important. For synchronized media, captions generally need to be accurate, properly synchronized with the audio, and to include relevant non-speech information. Auto-generated output is commonly used as a starting draft, but manual review and correction are typically needed to meet accessibility expectations. Automated tools also do not produce audio descriptions of visual content, which may be a separate requirement.
When does synchronized media require captions versus a transcript?
The appropriate approach generally depends on whether the media is time-based and whether it combines audio with synchronized visual content. Synchronized media that includes an audio track commonly requires captions so that the audio information is available in text while the media plays. Transcripts are often used as a supplement and, for certain content types, as an alternative. Which specific WCAG success criteria apply depends on factors such as whether the content is prerecorded or live and whether it is audio-only, video-only, or true synchronized media, so review the relevant criteria for your content type. This is general guidance and not a substitute for evaluating your specific content.
How do I decide whether audio description is needed for a video?
Audio description is generally needed when important information is presented visually and is not already conveyed through the existing audio track. If a video's narration or dialogue already describes the relevant on-screen action, additional description may be minimal or unnecessary. When key visual details, such as actions, text on screen, or scene changes, are not spoken, audio description helps convey that information to users who cannot see the screen. Reviewing the video for visual-only information that carries meaning is a common way to make this determination.
What conformance level should I target for synchronized media captions and descriptions?
Level AA is the level most commonly cited as a target in accessibility programs and in many settlements and guidance, though the specific level you should target depends on your obligations and context. Requirements for captions and audio description are distributed across success criteria at different levels within WCAG, so identifying the exact criteria that apply to your media type and your chosen conformance level is important. Because obligations can vary by jurisdiction and context, consult qualified legal counsel and current agency guidance when determining your target.
Does providing captions and audio description guarantee the media is accessible and legally compliant?
No. Meeting the relevant success criteria for captions and audio description reduces barriers but does not by itself guarantee an accessible experience for all users or immunity from legal claims. Quality matters, captions must be accurate and synchronized, and descriptions must convey the meaningful visual information. Manual review and testing with assistive technology are generally needed, since automated tools detect only a portion of issues and cannot fully assess caption accuracy or description quality. This entry is general information and not legal advice.

Common misconceptions

Synchronized media only refers to videos with sound.
The term describes any presentation that coordinates an audio component with a visual component along a shared timeline. The key attribute is the synchronized, time-based relationship between the two, which affects which accessibility techniques (such as captions and audio description) apply.
Adding captions makes synchronized media fully accessible and compliant.
Captions address one part of accessibility, primarily for users who are deaf or hard of hearing. Users who are blind or have low vision may also need audio description or an equivalent alternative. Meeting individual WCAG success criteria does not by itself guarantee a fully accessible experience for all users or immunity from legal claims.
Automatically generated captions are sufficient to meet accessibility requirements.
Automated tools may produce errors and typically do not reliably capture speaker changes, meaningful sounds, or accurate wording. Manual review and correction are generally needed, and automated processes detect only a portion of potential issues.

Best practices

Provide synchronized captions that accurately convey spoken dialogue and meaningful sounds, and review automatically generated captions manually for accuracy before publishing.
Add audio description for prerecorded synchronized media so that important visual information is available to users who cannot see the screen.
Offer a transcript that combines audio and visual information as an additional text alternative that can be read or accessed with assistive technology.
Identify the target WCAG version and conformance level for your project, noting that Level AA is the level most commonly cited as a target and that some criteria for synchronized media appear at Level A while others appear at Level AA.
Test synchronized media with manual review and assistive technology in addition to automated checks, since automated testing detects only a portion of accessibility issues.
Consult qualified legal counsel and current agency guidance to confirm which authority applies to your context, as requirements evolve through regulation and case law and this guidance is not legal advice.