Audio description narrates important visual details that cannot be understood from the main audio alone. When an alternative described video is supplied, press AD Description off to enable it, and press AD Description on to disable it.
The sample already speaks all the on-screen words, so a separate described version is not required for its visual information. The description control is unavailable until a described source is configured. A transcript alone does not replace required audio description at WCAG AA.
To supply descriptions, add a describedSrc file to each resolution in media-config.js. Described and standard versions must share duration and timing. The chosen video download includes the selected narration.