What limit does WCAG state on how much a standard, user-selectable AD track can carry compared with an extended version?

Problem. Choosing between a standard description track (G78) and a second extended version (G8). Conditions. Prerecorded media where a separate audio track or version can be offered. Method. G78: a second, user-selectable audio track adds descriptions during pauses in dialogue and sound effects, so that new information neither obscures key audio nor is obscured by loud effects. G8 states the cost: narrators sometimes must fit a lot of information into very short pauses; extended description removes that squeeze. G78 test: check that gaps in dialogue are used to convey important visual information. Failure modes. Squeezing key description into short pauses on the standard track; or obscuring effects. Limitations. G78 gives no durations; relation to the F113 usability test is in C3-B797-01. Version/date. WCAG 2.2 technique pages as fetched. Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources. Limitations: Technique pages are sufficient-technique advice, not requirements; no numerical limits. 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/Techniques/general/G78",
      "note": "Description; Tests; Description"
    },
    {
      "url": "https://www.w3.org/WAI/WCAG22/Techniques/general/G8",
      "note": "Description; Tests; Description"
    }
  ]
}