One audio description order placed through orders[], with download links once status is complete. Links expire after 8 hours; call again for fresh ones. The callback POSTs this same body. An unknown id is 404. An order placed another way keeps the response shape it was ordered with.

Download types: vtt, txt, json (description text); wav, mp3, ogg (description audio); mp4, mkv (media mixed with the description). Which ones are present depends on the order.