Is audio description needed when dialogue already carries the visual information, and how do WCAG 1.2.3, 1.2.5 and 1.2.8 layer?

Problem. Deciding whether a video needs description and which text alternative satisfies which level. Conditions. Prerecorded synchronized media, WCAG 2.2. Method. The Understanding page notes that if all important information in the video track is already in the audio track, no additional description is necessary. Standard AD means narration added during existing pauses in dialogue. 1.2.3 (A) allows audio description or a full text alternative; 1.2.5 (AA) requires audio description; 1.2.8 (AAA) requires an extended text description, adding nothing new only if 1.2.3 was met with a text description and 1.2.5 with audio. Failure modes. Treating a talking-head video as needing nothing without checking; assuming text alternative satisfies AA. Limitations. Says nothing about script timing numbers. Version/date. WCAG 2.2 Understanding page as fetched. Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources. Limitations: Prior candidate C3-B589-09 covers the level mapping broadly; this adds the no-gap-needed note and 1.2.8 layering only. DCMP Description Key (HTTP 403 to curl) and the ACB ADP guideline pages (404 at tried URLs) could not be fetched, so no DCMP/ACB gap-timing rule is claimed here; only W3C WCAG 2.2 pages were read. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

{
  "citations": [
    {
      "url": "https://www.w3.org/WAI/WCAG22/Understanding/audio-description-prerecorded.html",
      "note": "Intent, Note; Key Terms, Note 2; Intent"
    }
  ]
}