What are Accessible Media Types?

What are accessible media types?

Accessible media types are the alternative formats that let people use audio and video without hearing or seeing it: captions and transcripts for sound, and audio description for important visuals. WCAG calls audio and video "time-based media" and covers them in guideline 1.2. The goal is that every person gets the same information, whichever sense they use.

The main formats

• Captions: a synchronized text version of speech and of non-speech sound, such as a door slam or music that matters to the story. W3C separates captions from subtitles: captions are in the same language as the audio, subtitles translate it.
• Transcripts: a text version of the audio, and for video also the visual information. A transcript can be read at the user's own pace, used with a braille display and searched. W3C notes that captions and transcripts hold the same text, so one can be built from the other.
• Audio description: narration added to the soundtrack to describe important visual details that cannot be understood from the main soundtrack alone.
• Sign language: a sign language interpretation of the audio, aimed at users for whom it is a first language.
• Accessible player controls: a player that works with a keyboard and a screen reader, with labelled buttons for play, pause, volume, captions and description.

What WCAG 1.2 requires

Level AA is the usual target in procurement and accessibility law. Separately, SC 1.4.2 (Level A) says audio that starts automatically and runs longer than 3 seconds needs a way to pause or stop it, or to control its volume independently of the system volume. Read the full text in the WCAG guidance on w3.org.

Example

A product demo video shows a presenter clicking through a dashboard while talking. To make it accessible, add captions that include the speech and relevant sounds, and a transcript below the video. Where the presenter says "click here" without saying what, either change the script so the narration carries the information or add audio description. Finally, check that the player can be reached and operated with the keyboard.

Common mistakes

• Relying on auto-generated captions without reviewing names, product terms and punctuation. Automatic output is a starting point, not a finished caption file.
• Captioning speech but leaving out meaningful non-speech sound.
• Treating a transcript as a replacement for captions. They serve different needs, and the criteria ask for captions on synchronized media.
• Describing visuals only in the video and never in the narration, so blind users miss them.
• Autoplaying audio with no pause control.
• Burning captions into the video image, which users cannot resize, restyle or translate.

Accessible media, testing and performance

Media decisions affect users of assistive technology directly, and they sit next to other content rules such as accessible images and accessible color palettes. To record what you meet and what you do not, an accessibility conformance report lists each criterion. Automated tools can flag a missing track element but cannot judge caption quality, so combine them with manual review; the article Why performance testing must include accessibility explains what automated checks can and cannot say. Video-heavy pages are also often slow pages, so track them with LoadFocus page speed monitoring.

FAQ: Accessible Media Types

What is the difference between captions and subtitles?

Captions are in the same language as the audio and include non-speech sound, so they serve people who are deaf or hard of hearing. Subtitles translate the speech into another language and are not by themselves an accessibility accommodation.

Do I need audio description for every video?

Not for every video. WCAG asks for audio description or a media alternative at Level A and audio description at Level AA when important visual information is not available in the soundtrack. If the narration already says everything shown, there is little left to describe.

Is a transcript enough instead of captions?

No, for video with sound WCAG asks for captions. A transcript is a useful addition and is one of the ways to meet the alternative requirements, but it does not replace synchronized captions.

Are live streams covered?

Yes. SC 1.2.4 asks for captions for live audio in synchronized media at Level AA.

Can I use automatic captions?

You can use them as a first draft, then review and correct them. The requirement is that captions are accurate and complete, not that they were produced by a person.