Autoplay control and flashing content
Controls that stop unwanted motion and limits that keep blinking or flashing content from creating distraction or seizure risk.
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What it is
Autoplay control means people can pause, stop, or hide content that starts moving or updating without their request. Flashing content adds a separate safety limit: WCAG 2.3.1 permits no more than three flashes in any one-second period unless the flash is below its defined size and intensity thresholds. This protects people with photosensitive seizure disorders, while pause controls also help people who cannot read or concentrate beside constant movement. The reason the limit exists is a 1997 Pokemon episode whose red and blue strobe sequence sent hundreds of Japanese children to hospital in one evening.
Reach for it with carousels, background video, animated ads, blinking alerts, live tickers, and auto-refreshing panels. Under WCAG 2.2.2, moving, blinking, or scrolling content that starts automatically, lasts more than five seconds, and runs alongside other content needs a way to pause, stop, or hide it. Automatically updating content shown alongside other content needs the same controls or a way to set its update frequency. A real pause button should stop the underlying media or animation, not merely cover it.
Gotcha: muted autoplay is a browser permission workaround, not an accessibility control. The video is still moving. prefers-reduced-motion is useful as an automatic default, but it does not replace an on-screen control. Avoid rapid flashing entirely when you can; checking the precise WCAG flash thresholds takes analysis, not a designer's visual guess.
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Audit this interface for content that starts or changes on its own. Add a visible, keyboard-operable pause or stop button for every autoplaying video, carousel, ticker, looping animation, and auto-refreshing panel; the control must call HTMLMediaElement.pause(), cancel the Web Animations API Animation, or stop the actual update timer. Start nonessential motion paused under @media (prefers-reduced-motion: reduce), but keep the manual control available. Remove rapid blinking where possible. Otherwise verify WCAG 2.3.1 Three Flashes or Below Threshold by running the clip through PEAT, the free Photosensitive Epilepsy Analysis Tool from the Trace Center, or a broadcast Harding test, never by eye, and keep the rate at no more than three flashes in any one-second period. Report each autoplaying or flashing element, its risk, and the control or removal you implemented.