Audio description (described video) is a separate narration track that describes important visual elements - actions, scene changes, on-screen text - in the gaps between dialogue, so blind and low-vision viewers can follow the content. It is the visual-accessibility counterpart to captions.
Delivering it means carrying an additional audio track through the encoding ladder, packaging, and player, with UI to select it, plus the production work of authoring the descriptions. Audio description is increasingly mandated by accessibility law for certain content and is part of the broader accessibility obligation - alongside captions and WCAG conformance - that OTT platforms must plan for rather than retrofit.
