Add a sign language video stream in SMIL 2.0
SM14 is a sufficient technique when used with G81, and it is SM13's arrangement in SMIL 2.0. The content video displays in one region while the sign language interpretation displays in another, synchronized with it. As with SM13, what this delivers is interpretation and not captions, and the two are different accommodations for audiences that overlap without matching. G81 is the partner that sets the terms. It asks for an interpreter the player can put in a separate viewport or overlay on the picture, so the viewer keeps some say in where it goes. The published test starts by enabling the control for interpretation, with an allowance for interpretation that is simply always shown. If you are not publishing SMIL, the practical modern shapes are two versions of the film published side by side, standard and signed, or an interpreter composited into a second track the player can bring up.
How we find it in an audit
Reviewers look for a signed version, and where one exists we watch it with a Deaf reviewer rather than grading it ourselves. The mechanical checks come first. Is the interpreter in sync, are they framed so hands and face are both readable, is the control to bring them up something a keyboard can reach. Then the judgment, which is whether the interpretation actually carries the content. That is not a question a hearing auditor can settle, and we do not pretend otherwise.
How affected users experience it
Sign language interpretation is offered far less often than captions. The gap is not about need. It is because interpretation costs more and captions look like they cover it. For a Deaf viewer whose first language is signed, a captioned video is a document to read while watching, and an interpreted video is a film in their own language. Offering both is the honest answer where the content matters enough to justify it, which for public information and safety material it usually does.
Passes vs. fails
Passes
<region id="main"/>
<region id="signer"/>
<par>
<video src="safety.mp4" region="main"/>
<video src="safety-signed.mp4" region="signer"/>
</par>
<!-- The interpreter has a region of their own, and the viewer can bring it up. -->Fails
<region id="main"/>
<par>
<video src="safety.mp4" region="main"/>
<textstream src="safety.rt"/>
</par>
<!-- Captions only. No interpretation offered anywhere. -->Other ways to satisfy this rule
4 guides on this site are filed under 1.2.6 Sign Language (Prerecorded). W3C lists this one as sufficient for that rule only alongside G81, so the pair is what passes and neither half does on its own.
This guide is our interpretation of W3C technique SM14: Providing sign language interpretation through synchronized video streams 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.