RE: confusion in 1.2.3 Audio Description or Media Alternative (Prerecorded)

From: Rakesh Paladugula [mailto:rakesh.paladugula@deque.com]
Sent: Sunday, May 15, 2016 2:37 AM

I am going through Understanding 1.2.3 Audio Description or Media Alternative (Prerecorded) at https://www.w3.org/TR/UNDERSTANDING-WCAG20/media-equiv-audio-desc.html this morning. Under the header Intent of this Success Criterion I found the following sentence
One approach is to provide audio description of the video content. The audio description augments the audio portion of the presentation with the information needed when the video portion is not available.

The last wording * video portion is not available* is really confusing me. I am in the opinion that it should be *Video portion does not convey the important information* or similar wording.
Am I missing something here? Can someone help me understand this better.

People who can’t perceive the video portion need spoken descriptions that convey in audio the important information provided in the video track.
The typical example (but not the only example) would be a person who is blind, for whom the video track is not perceivable.


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