Do not autoplay audio without a stop control
Sound that starts on its own and runs longer than three seconds needs a way to turn it off. A page without one has the defect, and F23 is the documented failure that names it under the audio control rule. Two routes satisfy the rule and most write-ups name only the first. A mechanism to pause or stop the audio counts. So does a mechanism to control that audio's volume separately from the system volume, which is a real option for a media-heavy site and is rarely offered. The placement everybody quotes comes from a different technique rather than from this failure, and it is still right. The control belongs near the beginning of the page, where somebody can reach it before the sound has driven them off. One more thing decides how far the finding reaches. Because autoplaying sound can stop a person using anything else on the page, every part of the page has to meet this rule, third-party embeds included.
How we find it in an audit
Reviewers load the page with the volume up and start counting. Anything past three seconds needs a control, and the control has to be findable without scrolling and operable from the keyboard. Automated tools can find an autoplay attribute, which catches the honest cases and misses everything built in script or loaded inside an advert. So a reviewer sits on the page and listens, third-party frames included, because the rule does not care who wrote them.
How affected users experience it
Autoplaying audio and a screen reader are competing for the same output device. The page starts talking over the software the user navigates with, and the first thing they lose is the ability to find the control that would stop it. Turning the system volume down turns the screen reader down too, so the usual workaround costs them the page. For people with cognitive disabilities the competing sound makes reading much harder, and for anyone using speech input, background audio can break recognition outright.
Passes vs. fails
Passes
<audio src="theme.mp3" controls></audio>
<!-- Plays when the user chooses, and the controls come with the element. -->Fails
<audio src="theme.mp3" autoplay loop></audio>
<!-- Starts on load, never stops, and offers nothing to stop it with. -->How this gets tested
The W3C publishes test rules that define what a checker looks for here.
- Audio or video element avoids automatically playing audioA tool can check this
- Audio or video element that plays automatically has a control mechanismA tool can check this
- Audio or video element that plays automatically has no audio that lasts more than 3 secondsA tool can check this
The other techniques filed under this rule
5 guides on this site are filed under 1.4.2 Audio Control. W3C documents this one as a failure of that rule, so it describes a way the rule gets broken rather than a way to pass it.
This guide is our interpretation of W3C technique F23: Failure of 1.4.2 due to playing a sound longer than 3 seconds where there is no mechanism to turn it off. 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.