48-Hour Call for Consensus (CfC): Proposed TTML Comments


This is a Call for Consensus (CfC) to the Accessible Platform
Architectures (APA) Working Group proposing the following review
response on:

ttml profiles for internet media subtitles and = captions 1.2  

This draft response was first posted to APA on 22 January last at:
It's language has been tweaked by yours truly.

<begin draft comment>

1.)    Reference to WCAG 2.1:  

We appreciate the addition of section
<https://www.w3.org/TR/2019/WD-ttml-imsc1.2-20191128/#wcag-applications> D.1
WCAG Considerations and its content.  This is very helpful.  We would, though,
like to change the phrasing "WCAG 2.1 recommends" to "WCAG 2.1 requires",
because the WCAG success criteria are normative requirements rather than

2.)    Requested Additional WCAG 2.1 References:  

In addition to the guidelines and success criteria you already reference, we
would like to see references to the following WCAG 2.1 success criteria that are
also applicable to the TTML profiles specification:

	a.        <https://www.w3.org/TR/2018/REC-WCAG21-20180605/#contrast-minimum> Success Criterion 1.4.3 Contrast (Minimum) (applying to the text-only profile)

	b.        <https://www.w3.org/TR/2018/REC-WCAG21-20180605/#non-text-contrast> Success Criterion 1.4.11 Non-text Contrast (applying to the image-only profile)

	c.        <https://www.w3.org/TR/2018/REC-WCAG21-20180605/#language-of-page> Success Criterion 3.1.1 Language of Page (using the xml:lang attribute)

	d.        <https://www.w3.org/TR/2018/REC-WCAG21-20180605/#language-of-parts> Success Criterion 3.1.2 Language of Parts (using the xml:lang attribute)

3.)    Reference to MAUR:  We also appreciate the addition of section D.2 MAUR
Thank you. We trust the MAUR will continue helpful to the wider community.

4.)     With respect to the
<https://www.w3.org/TR/2019/WD-ttml-imsc1.2-20191128/#altText> 7.12.2 altText
named metadata item, this is directly related to the accessibility requirement
of having an alternate text version for images (<https://www.w3.org/TR/2018/REC-WCAG21-20180605/#non-text-content> Success Criterion 1.1.1
Non-text Content). Could you add a note here saying something like: "Note:
Authors are encouraged to provide text alternatives for every non-decorative
image and/or compound image set by using the altText named metadata item. This is
necessary for making the image in the document accessible to persons with (visual)
disabilities, thus complying with
<https://www.w3.org/TR/2018/REC-WCAG21-20180605/#non-text-content> W CAG
2.1 success criterion 1.1.1 (Non-text content)."

5.)    Suggested Introduction Section for First-Time Readers: The document
would be easier to read and understand for first-time readers if it had an
introduction that guided the reader to a better understanding of its content.
Such an introduction could serve to introduce the reader to items such as the

	a.       Why are profiles needed for text-only and image-only captions/subtitles?

	b.       What are typical use cases for image-only captions/subtitles?

6.)    There is a general issue with the way that an author specifies layout
characteristics of captions and subtitles, such as font size, font family,
line height, background and positioning.  It should be made clear that authors
can and should define the viewport and text characteristics, but these
definitions may be overridden by the user by setting up their user agent to
better meet their particular needs as users (cf. MAUR, 3.7 Requirements on the
use of the viewport
For example, a user with vision impairment who also requires caption support
may want to have all captions displayed in the lower third of the screen with
a large font, disregarding the definition of various viewports and font types
defined by the author.  We recommend adding a note to the spec to advise
authors that  the final rendition of their document may not follow their
specified styling and positioning, but follow user-defined styling and
positioning instead.

7.)     <https://www.w3.org/TR/2019/WD-ttml-imsc1.2-20191128/#forced-content>
Section C. Forced content: This seems like a temporary solution to us.
Mightn't it be better to define semantic layers of information so that each
layer could be made visible and invisible at runtime as appropriate for the
user?  For example, the user might want to see either speech-only (subtitles),
narration speech only (parts of subtitles), foreign-language speech-only
(parts of subtitles) or some combination of these.


***Action to Take***

This CfC is now open for objection, comment, as well as statements of
support via email. Silence will be interpreted as support, though
messages of support are certainly welcome.

If you object to this proposed action, or have comments concerning this
proposal, please respond by replying on list to this message no later
than 23:59 (Midnight) Boston Time, Tuesday 25 February.

NOTE: This Call for Consensus is being conducted in accordance with the
APA Decision Policy published at:


Our thanks to Dr. Gottfried Zimmerman for reviewing the TTML
specification and providing us with his recommended response above as
logged in.  Action-2224<https://www.w3.org/WAI/APA/track/actions/2224>.


Janina Sajka

Linux Foundation Fellow
Executive Chair, Accessibility Workgroup:	http://a11y.org

The World Wide Web Consortium (W3C), Web Accessibility Initiative (WAI)
Chair, Accessible Platform Architectures	http://www.w3.org/wai/apa

Received on Wednesday, 19 February 2020 20:37:39 UTC