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Re: Captions not in Text-Format


From: Steve Green
Date: Sep 2, 2022 8:39AM

The WCAG definition of captions includes images of text embedded in video. The WCAG definition of an image of text states "text that has been rendered in a non-text form (e.g., an image)", which obviously fails the level AA success criterion 1.4.5 (Images of Text) even though the definition does not specifically mention video content. If you are only aiming to meet WCAG level A, this does not matter.
See https://www.w3.org/TR/WCAG21/#dfn-captions and https://www.w3.org/TR/WCAG21/#dfn-images-of-text

The WCAG level AAA success criterion 1.2.8 is specifically designed to address the requirements of people with both visual and hearing impairments. It requires that you provide all of the information in the synchronized media (both visual and auditory) in text form, presumably because this can be used with appropriate output devices such as Braille displays.

The WebVTT file would not usually be sufficient to meet SC 1.2.8 because it is not likely to contain the information that is presented visually in the video. The file also contains all the timing information, which would result in a lot of noise for screen reader users whether they are using audio output or a Braille display.

Steve Green
Managing Director
Test Partners Ltd

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Subject: [WebAIM] Captions not in Text-Format

Captions may be provided in a caption-file OR as pure graphic in a video.
The definition says: "synchronized visual and/OR text alternative."

So pure graphical captions pass SC 1.2.2 and 1.2.4.

But what about people who are hard of hearing AND visually impaired?

And what about SR users who want to find out the correct spelling of an unknown term or name?

"For optimum accessibility, provide a separate caption file of the description of visual information."

( <https://www.w3.org/WAI/media/av/captions/>

1. Are graphical captions an issue for SC 1.4.5 Images of text? Neither the
Understanding examples nor techs suggest that.

2. Is there any other SC that covers the problem?

3. Is a caption file (WebVTT, .) the obvious text alternative regarding to SR support?

Thanks for clarification!