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Perceivable WCAG 1.2.7

1.2.7 Extended Audio Description (Prerecorded)

Where pauses in foreground audio are insufficient for audio descriptions, extended audio description must be provided by pausing the video to allow complete descriptions of visual content.

Level AAA Moderate WCAG 2.0 (new) WCAG 2.1 WCAG 2.2

What this rule means

WCAG 1.2.7 addresses situations where the natural pauses in a video's audio track are too short to fit adequate audio descriptions. In these cases, the video must be paused to allow the description to play, then resumed önce the description is complete. This is known as "extended audio description."

This Level AAA criterion builds on 1.2.5 by removing the constraint that descriptions must fit within natural pauses. It ensures that even dialogue-heavy or fast-paced content can be fully described for blind and low-vision users.

Why it matters

Many videos — particularly educational content, documentaries, and dramatic productions — have continuous dialogue or narration with few natural pauses. Standard audio description (1.2.5) cannot adequately describe complex visual content when there is no room in the audio timeline. Extended audio description solves this by temporarily freezing the video.

Without extended audio description, blind users watching dialogue-heavy content with significant visual elements receive an incomplete experience. The descriptions are either crammed into inadequate spaces or omitted entirely.

Related axe-core rules

No axe-core rules address extended audio description. This criterion requires manual testing and human judgment about the adequacy of existing pause durations for audio descriptions.

How to test

  1. Identify prerecorded videos where standard audio description cannot fit all necessary visual information into natural pauses.
  2. Verify that an extended audio description option is available.
  3. Play the video with extended audio description enabled.
  4. Confirm that the video pauses automatically to allow descriptions to complete before resuming playback.
  5. Verify that all critical visual information is described, even for scenes with continuous dialogue.
  6. Check that the user experience is not jarring — transitions between paused and playing states should be smooth.

How to fix

Implement a custom video player that supports pausing for extended descriptions:

class ExtendedAudioDescPlayer {
  constructor(videoEl, descriptions) {
    this.video = videoEl;
    this.descriptions = descriptions; // sorted by time
    this.synth = window.speechSynthesis;
    this.video.addEventListener("timeupdate", () => this.check());
  }

  check() {
    const t = this.video.currentTime;
    const desc = this.descriptions.find(
      d => Math.abs(d.time - t) < 0.5 && !d.played
    );
    if (desc) {
      this.video.pause();
      desc.played = true;
      const utterance = new SpeechSynthesisUtterance(desc.text);
      utterance.onend = () => this.video.play();
      this.synth.speak(utterance);
    }
  }
}

const player = new ExtendedAudioDescPlayer(
  document.querySelector("video"),
  [
    { time: 5.0, text: "A complex diagram shows the network topology with six interconnected nodes.", played: false },
    { time: 22.0, text: "The screen splits into four quadrants, each showing a different camera angle.", played: false },
  ]
);

For server-side implementation, create an alternate version of the video with built-in pauses:

<div role="region" aria-label="Video with extended audio description">
  <video controls>
    <source src="/lecture-extended-ad.mp4" type="video/mp4" />
    <track kind="captions" src="/lecture-captions.vtt" srclang="en" default />
  </video>
  <p>This version includes extended pauses for complete audio descriptions.</p>
</div>

<p>
  <a href="/lecture-standard.mp4">Watch standard version (without extended descriptions)</a>
</p>

Common mistakes

  • Assuming standard audio description is always sufficient without evaluating the actual pause durations.
  • Implementing extended description in a way that causes audio/video synchronization issues when playback resumes.
  • Not providing a toggle to switch between standard and extended description modes.
  • Pausing the video at awkward moments that disrupt the viewing experience unnecessarily.
  • Using only text-to-speech for extended descriptions without professional narration for quality content.

Resources