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Success Criterion 1.2.3 - transcripts and audio description

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From: Jason Kiss
Date: Jun 9, 2011 10:48PM

I'm probably just being thick in my reading of this particular Success
Criterion, but I would love to get some input from others on this to help
me.

WCAG 2.0 Success Criterion 1.2.3 [
http://www.w3.org/TR/WCAG20/#media-equiv-audio-desc] says that "An alternative
for time-based media
<http://www.w3.org/TR/WCAG20/#alt-time-based-mediadef>;or audio
description <http://www.w3.org/TR/WCAG20/#audiodescdef>; of the
prerecorded<http://www.w3.org/TR/WCAG20/#prerecordeddef>;
video <http://www.w3.org/TR/WCAG20/#videodef>; content is provided for
synchronized
media <http://www.w3.org/TR/WCAG20/#synchronizedmediadef>;, except when the
media is a media alternative for
text<http://www.w3.org/TR/WCAG20/#multimedia-alt-textdef>;and is
clearly labeled as such."

On the Understanding Success Criterion 1.2.3 page [
http://www.w3.org/TR/UNDERSTANDING-WCAG20/media-equiv-audio-desc.html], Note
1 says "if all of the information in the video track is already provided in
the audio track, no audio description is necessary." On that same page, Note
2 says that "in Success Criterion 1.2.3, authors do have the choice of
providing either an audio description or a full text alternative."

Let's say we have an audio-video clip for which the video track is purely
incidental and adds no additional meaning. In other words, remove the video
track, and all the meaningful content remains in the audio track. Does
Success Criterion 1.2.3 enable someone to say, "Okay, I'm going to provide
an audio description for this video instead of a text transcript, and since
there is no information in the video track to add to an audio description,
I'm all done." For instance, could someone in this case provide an
additional audio description track that is effectively empty or silent, and
reasonably claim that they've complied with 1.2.3?

Or, because there is no meaningful audio description to provide, does 1.2.3
thereby require that a transcript be provided?

I realize that for such an audio-video clip, if properly captioned, all the
meaningful content is available to visually impaired users via the audio
track, and to hearing impaired through the captions. And for the record, I'm
a fan of providing transcripts, even in cases like these where the video
track is mostly irrelevant, because they are generally more complete and
descriptive than audio description to begin with. I am really just wondering
about how to read this particular Success Criterion, which seems a little
ambiguous to me. Am I missing something or reading this wrong?

Thanks.

Jason