RE: Magnified Caption Files

Hi John, I agree this is a tricky area.  I do not consider browser zoom to be an assistive technology.  I would agree with the LVTF that we are not concerned with AT magnification here – as any issue would be between the user agent and the AT.  We would be concerned with both browser zoom and other types of changes such as font word/line changes per WCAG 2.1 and changes in font such as those covered by the aforenoted CVAA requirements in the US.

There certainly are limitations as the APA notes – captions can be provided over the video or in a separate area such as below the video.  The size of caption text could increase either though video player settings or by stylesheet changes and having a buffer in place could help with some degree of increase without overlapping key content – but again this would be very tricky to test across videos do to placement of key content and how the narration was captioned, size of the video content such as mini players that are popular on pages, etc.

Ultimately being able to display closed captions in a user controllable way may mean that the user sometimes does something that makes content unreadable --  but this may be their choice.  However author recommended values should still be available if the user chooses not to overwrite them.  If the caption information was available programmatically so it could be in a separate windows/screen or overlayed would give the user the ultimate choice if they choose to override placement and other characteristics.

Jonathan

From: John Foliot [mailto:john.foliot@deque.com]
Sent: Wednesday, February 7, 2018 3:47 PM
To: W3C WAI Accessible Platform Architectures <public-apa@w3.org>; public-low-vision-a11y-tf <public-low-vision-a11y-tf@w3.org>
Subject: Magnified Caption Files

(copying the WCAG Low Vision TF)

All,

As you are possibly aware, we are currently closing off some old comments with the VTT Working Group (with spill-over to the TTML / IMSC Working Group) around the ability to enlarge caption text to support Low Vision users.

Sylvia Pfeiffer responded with the following:

If I understand correctly, you'd like me to add authoring guidance around magnification and its potential impact.

Could it be done with a single paragraph such as:
"Authors of WebVTT caption and subtitle files are encouraged to test the rendering of their files using Assistive Technology. Specifically, the use of magnification tools by low-vision users may require editing their files to allow for sufficient space within cue lines and cue line heights. It is recommended to allow for a 200% magnification without clipping."

My personal opinion is that this is effectively what we seek (Ref: WCAG SC 1.4.4 Resize Text), but before I respond more formally to the GitHub issue (https://github.com/w3c/webvtt/issues/426) I'd welcome some feedback.

LVTF, does this sound right? LV members, have you encountered something like this previously? (the ability to enlarge caption files independent of the video?)

APA - are we comfortable with Sylvia's proposal? Would something like this also meet our needs with the TTML / IMSC group?

Given that the VTT WG are keen on disposing with all comments, I'd like to try and resolve this one fairly quickly.

Thoughts?

JF
--
John Foliot
Principal Accessibility Strategist
Deque Systems Inc.
john.foliot@deque.com<mailto:john.foliot@deque.com>

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