SM7Sufficient technique WCAG 1.2.3 WCAG 1.2.5 Level A Human testing required

Add audio description in SMIL 2.0

SM7 is a sufficient technique when used with G173, filed against both criteria above, and it is SM6's method in SMIL 2.0. The description fits in the gaps in the dialogue and rides alongside the main soundtrack as a stream the viewer switches on. The first step of the published test is finding the control that switches it on. That is where implementations usually go wrong. A described track nobody can find is a described track nobody uses. W3C's own worked example for this one names the RealMedia player, which is a fair indication of when the technique was written. That is not an argument against the accommodation, only against the container. Audio description matters exactly as much as it did. The delivery today is a described audio track on an HTML5 video, or a described version published beside the original with the link somewhere a viewer will meet it.

How we find it in an audit

We look for the control before we look at the content, because a description track a viewer cannot enable has not been delivered. So three questions come first. Where is the switch, is it reachable from the keyboard, and does a screen reader announce what it does. Then the description itself gets watched and graded against a list of what the picture carries that the soundtrack does not. Scanners can confirm the absence of a track and stop there. Judging coverage is a person watching the whole film.

How affected users experience it

Two things go wrong. Only one is about the film. The first is missing description, where the visual story is simply absent. The second is description that exists behind a control nobody can operate, which is worse in one specific way. The site has done the expensive part, paid a describer, produced the track, and then hidden it behind a menu that needs a mouse. The viewer gets the same experience as a site that never bothered, and the site believes it has solved the problem.

Passes vs. fails

Passes: narration speaks the visuals. Fails: the offer is never spoken.

Passes

<par>
  <video src="briefing.mp4"/>
  <audio src="soundtrack.mp3"/>
  <audio src="briefing-described.mp3"/>
</par>
<!-- The player exposes the description stream as a switch the viewer can find. -->

Fails

<par>
  <video src="briefing.mp4"/>
  <audio src="soundtrack.mp3"/>
</par>
<!-- No description stream, and no control to ask for one. -->

How this gets tested

The W3C publishes test rules that define what a checker looks for here.

Video element visual content has accessible alternativeA tool finds candidates, you decide
Video element visual content has strict accessible alternativeA tool finds candidates, you decide

Other ways to satisfy this rule

13 guides on this site are filed under 1.2.3 Audio Description or Media Alternative (Prerecorded). W3C lists this one as sufficient for that rule only alongside G173, so the pair is what passes and neither half does on its own.

This guide is our interpretation of W3C technique SM7: Providing audio description in SMIL 2.0. W3C publishes its techniques as guidance rather than as the standard, and says so on every one of them. The success criterion is what conformance is measured against, and a technique is one documented way to meet it.