media-alternative-transcript-evidence
Time-based media: transcript or text alternative evidence
Finds audio and video elements where a transcript or other text alternative is not strongly evidenced in the page content. This rule is conservative and reports cantTell when evidence is missing or cannot be verified.
Applies to. Any eligible <audio> or <video> element in the composed DOM.
Expectation. If a strong transcript/text-alternative signal is present (e.g., aria-describedby binding to a visible transcript block, or a nearby clearly labeled Transcript section/link), no occurrence is reported. Otherwise, the rule reports cantTell (insufficient evidence) for that media element.
Examples
<video src="talk.mp4" controls aria-describedby="t1"></video><div id="t1">Transcript: Welcome to today's talk...</div>
`aria-describedby` binds to text explicitly identified as a transcript — strong evidence.
<video src="talk.mp4" controls></video>
No transcript or text-alternative evidence was found near the media element; the engine can't confirm one doesn't exist elsewhere on the page, so this is conservative, not a fail.