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.
What a finding reports.
evidence.strength: how strong the transcript signal found near the media is:none(transcriptNotDetected) orweak(transcriptEvidenceUnverified).evidence.method: what was found:none,anchor-unverified(a transcript link to a part of the same page that does not look like a transcript) orexternal-link(a transcript link to another page, which is not followed).evidence.transcriptLinkHref(a weak signal): the transcript link'shref.evidence.transcriptNodeSelector(a weak signal): a selector for the transcript link.evidence.notes: short English notes on what was found. Empty when nothing was.
These data.details fields help to read and reproduce a finding. Apart from reasonCode and the few fields Output schema names as stable, they are not a stable contract: a field may be renamed or dropped in a minor release, so don’t build on them.
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.
How to check
When this rule can’t decide, it reports cantTell and leaves the question to a person. Each question it can ask is listed here under its reason code, with the steps to answer it. A finding carries the same steps as howToCheck, in the scan’s language. See Output schema.
transcriptNotDetected
- Find the audio or video player the report names and play it, noting whether it has sound, pictures or both.
- Look next to the player and elsewhere on the page for a transcript or a link to one.
- If it is a video with no sound, an audio version that describes everything shown also counts, as long as you can find it and play it from the page with the keyboard.
- Compare the alternative you found with the media and check that it gives the same information: speech, important sounds and what is shown.
Pass. A transcript or text alternative is on the page or linked next to the player and gives what the media gives; or a video with no sound has an audio version that gives the same information; or the media is itself an alternative for text on the page and is labelled as such.
Fail. Prerecorded audio-only media has no transcript, or prerecorded video-only media has neither a transcript nor an audio version with the same information, which fails WCAG 1.2.1.
transcriptEvidenceUnverified
- Find the link next to the player the report names (the report gives its href).
- Follow the link and check that it leads to a transcript of this media.
- If the link is not a transcript, the media may still have one elsewhere on the page or, for a video with no sound, an audio version that describes what is shown. Look for it before deciding.
- Compare the alternative you found with the media and check that it gives the same information: speech, important sounds and what is shown.
Pass. The link, or another transcript on the page, gives what the media gives; or a video with no sound has an audio version that gives the same information.
Fail. Neither the link nor anything else on the page gives the media's information as text, or, for a video with no sound, as audio, which fails WCAG 1.2.1.