Autoplay

Autoplay is any feature that begins playback without the reader specifically asking for it, whether the request is spelled as an autoplay attribute in markup or as a script calling play(). The word used to describe a promise browsers kept. It no longer does. Sound requires user activation, meaning a click, a tap or a keypress inside the page, so an unmuted request is refused and the promise play() hands back is rejected instead. A muted request is granted. That single fork is the whole of the modern policy, and it is why the term has quietly come to mean a silent moving picture rather than playback.

The policy rewrote the interfaces around it. Because sound is off, the picture has to carry the entire message, which is why feeds ship a text track or burn the words into the frame (see captions) and why the poster frame stopped being a formality: it is the only thing a reader judges the clip by before deciding to grant the gesture. It is also why a muted loop with no controls is a moving image rather than a video player, and why the one control such a clip really owes is the one that turns the sound on, since that tap is the activation the browser was waiting for. Vendors add a wrinkle worth knowing: a reader who watches media on a site often enough may earn autoplay with sound there, so a feature that works on your own machine can be refused on everyone else’s.

Getting permission is not the same as being welcome. Playback that nobody asked for is motion nobody asked for, and the reader who has said so through prefers-reduced-motion has said it about your hero loop too. The sharpest version of the cost is flashing content, where an autoplaying cut can reach a rate that triggers seizures in a reader who never pressed play. The web’s two answers are written as success criteria rather than as advice. WCAG 1.4.2 covers sound, and the term for satisfying it is audio control. WCAG 2.2.2 covers anything moving for more than five seconds, and the term there is pause, stop, hide. Autoplay is the behaviour; those two are the remedies, and a design that ships the first without either of the others has shipped a defect.

The honest uses are narrow and they share a shape: the reader arrived for the media. A clip opened in a lightbox may start on its own, because opening it was the gesture. A short muted loop standing in for an animated illustration is fair, given a way to stop it. What is never fair is sound, on any page, on the strength of a request the reader did not make.