Audio description is a secondary narration track inserted into natural pauses in a video — or played over the content in an extended version — that describes what is happening on screen for learners who are blind or have low vision. WCAG 2.1 AA Success Criterion 1.2.5 requires audio description for all pre-recorded video content where the visual track conveys information not present in the audio alone. In e-learning, this typically applies to demonstration videos, software walkthroughs, and diagram-heavy instructional content where a sighted viewer understands the lesson partly through what they see rather than hear. Audio description is either recorded by a narrator reading a prepared script and mixed with the original audio, or generated synthetically via text-to-speech with lower naturalness. The production challenge is that inserting description requires either natural pause space in the original video or the creation of an extended audio-description version where the video is paused mid-scene to fit the narration. This makes retrofitting audio description to existing content expensive; the best practice is to write scripts with sufficient verbal explanation from the start, reducing the visual-only information that would need description. Audio description is distinct from captions, which address the hearing-impaired; together they form the dual accessibility requirement for most pre-recorded learning video.
