Perceivable · 1.2 Time-based Media

Extended Audio Description (Prerecorded) WCAG 1.2.7 · Level AAA

Where natural pauses in a prerecorded video's audio are too short for audio description to convey the visual content, the video must pause while extended description plays, so no important visual information is lost.

Level
AAA
Since
WCAG 2.0
Principle
Perceivable
Guideline
1.2 Time-based Media
Try the live demo All criteria Checklist

Live demo

Hear a fast tutorial with extended description

The same task, done two ways: switch between the version that passes and the one that fails, or put them side by side. Everything in the box is live, so try it with a keyboard, a pointer or a screen reader.

Press play and listen without looking. In Passes the video stops while each screen is described; in Fails the descriptions have to fit into gaps that are too short.

Live example

Passes

Turn on two-step sign-in

A fast tutorial from your bank's help center.

What happened

    Why it passes

    The video pauses while each description is read, then carries on. A blind viewer hears which option to pick, what the code screen shows and where the backup codes are.

    Why it fails

    The trainer barely pauses, so the descriptions either talk over him or leave details out. A blind viewer misses which option to choose and what "press this" means.

    Examples

    Code that fails, and the fix

    Four examples, each one running: the usual ways this criterion fails, and code that passes. Listen to them, measure them, or copy the code.

    01What changes 5 lines

    Fails

    Descriptions spoken over a playing video

    Live preview

    JavaScript
    const video = document.querySelector("#two-step-video");const track = video.textTracks.getTrackById("desc");track.mode = "hidden";track.addEventListener("cuechange", () => {  const cue = track.activeCues[0];  if (cue) speechSynthesis.speak(new SpeechSynthesisUtterance(cue.text));});

    The description is spoken while the video keeps playing. Where the gaps in the speech are short, it talks over the trainer or runs into the next screen.

    Passes

    Video pauses while each description is read

    Live preview

    JavaScript
    const video = document.querySelector("#two-step-video");const track = video.textTracks.getTrackById("desc");track.mode = "hidden";track.addEventListener("cuechange", () => {  const cue = track.activeCues[0];  if (!cue) return;  video.pause();  const line = new SpeechSynthesisUtterance(cue.text);  line.addEventListener("end", () => video.play());  speechSynthesis.speak(line);});

    When a description cue starts, the video pauses, the description is read in full, and the video carries on when it ends.

    Passes

    Description track the script reads

    Live preview

    HTML
    <video id="two-step-video" controls src="/help/two-step.mp4">  <track kind="captions" src="/help/two-step.en.vtt" srclang="en" label="English">  <track id="desc" kind="descriptions" src="/help/two-step.desc.vtt" srclang="en" label="Audio description"></video>

    The descriptions sit in their own text track, so they can be as long as they need to be; the script above pauses the video to read each one.

    Passes

    Separately edited extended version

    Live preview

    HTML
    <video controls src="/help/two-step.mp4"></video><p><a href="/help/two-step-extended.mp4">Watch with extended audio description</a></p><p>This version runs 8 minutes instead of 6. The picture holds still while each screen is described.</p>

    The extended version was edited to freeze the picture during each description, so it runs longer but leaves nothing out.

    Why it matters

    Who it helps

    Blind and low-vision people get complete descriptions of fast or dense videos, such as training material, where standard description would have to leave details out.

    W3C: Understanding 1.2.7

    • Level AAA

      Level AAA is the highest level. It is not required for whole sites, but it is worth meeting where you can.

    • In WCAG versions

      Part of WCAG 2.0 since December 2008, and of every version after it.

      WCAG 1.0 checkpoints: 1.3, 1.4

    • Where it is required

      No law on this site requires Level AAA criteria for whole sites.

    How to test

    Checking it

    A few concrete steps. Automated tools find some failures; most need a person.

    1. Watch the audio-described version and note any visual information skipped because the pauses were too short.
    2. Confirm that where pauses cannot fit the description, the video freezes while extra description plays and then resumes.

    Common failures

    Where it breaks

    • Standard description squeezed into short gaps leaves out on-screen steps or text.
    • Descriptions talk over the dialogue instead of pausing the video to make room.

    Related