Add audio description in SMIL 1.0
SM6 is a sufficient technique when used with G173, the general technique for a described version of a movie, and it covers both of the criteria shown above. This is ordinary audio description rather than the extended kind. The difference is one constraint. The description has to fit in the gaps in the dialogue, so nothing pauses and the running time does not change. A parallel audio stream carries the description alongside the main soundtrack, and the user turns it on. Note the partner technique, because it is what separates this pair from SM1 and SM2. G173 goes with ordinary description and G8 goes with the extended kind, and choosing between them is really choosing whether your soundtrack has room. The published test allows for description that is simply always on, which is open description, and that conforms too. If you are not publishing SMIL, the modern shape is a selectable described audio track on an HTML5 video.
How we find it in an audit
A reviewer watches with the picture, then listens without it. Everything that went missing gets written down. Names on screen, a location caption, a chart, a facial reaction that changes what a line means. Then we look for a description track and, if there is one, judge whether it covers that list. Automated tools can tell you no described track was published. Whether the description that exists is any good is a human watching a film with a notepad, and it is the only method there is.
How affected users experience it
A blind viewer follows the dialogue perfectly and misses the film. Two people stop talking and something happens. A caption gives the date and place and nobody reads it aloud. The demonstration works, and the reason it worked was visible rather than spoken. Description written into the pauses fixes all of that without asking anybody to watch a different version, which is why it is the option most viewers prefer when it is offered.
Passes vs. fails
Passes
<par>
<video src="tour.mp4"/>
<audio src="soundtrack.mp3"/>
<audio src="described.mp3"/>
</par>
<!-- The description track plays in parallel, inside the gaps in the dialogue. -->Fails
<par>
<video src="tour.mp4"/>
<audio src="soundtrack.mp3"/>
</par>
<!-- One audio stream. Everything shown and not said is lost. -->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.
- G8sufficientProvide a version with extended audio descriptions
- G58sufficientPut the media alternative link beside the media
- G69sufficientProvide a full transcript of the media
- G78sufficientOffer a selectable audio description track
- G173sufficientOffer a described version of every video
- G203sufficientDescribe talking-head video with static text
This guide is our interpretation of W3C technique SM6: Providing audio description in SMIL 1.0. 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.