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

Colleagues:

This is a Call for Consensus (CfC) to the Accessible Platform
Architectures (APA) Working Group on our review of the ttml profiles for
internet media subtitles and captions 1.1 specification:

https://www.w3.org/tr/ttml-imsc1.1/

<Begin draft comment>

1. While we appreciate that TTML Profiles for Internet Media Subtitles and Captions 1.1 <https://www.w3.org/TR/ttml-imsc1.1/>  is depending on Timed Text Markup Language 2 (TTML2) <https://www.w3.org/TR/ttml2/> , it should still include an introduction that guides the reader to a better understanding of its content.  Such an introduction could respond to the following questions:

a. Why are profiles needed for text-only and image-only captions/subtitles?
b. What are typical use cases for a image-only captions/subtitles?
c. What is the purpose of a presentation processor, and a transformation processor?

2. 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.  The spec describes the approach of the author specifying a “fixed layout” for captions and subtitles that the user cannot change.  However, it must be possible for the user to overwrite the author’s choice of font size, or background color, for example. This is necessary for accessibility reasons, in the same way that browsers allow the user to change font size and background color.  How can we find a good solution for these conflicting interests between author and user?  We would like to get into a discussion with you on this issue. 

3. Section 2 Documentation Conventions (applies also to Timed Text Markup Language 2 (TTML2) <https://www.w3.org/TR/ttml2/>  section 2.3). For accessibility of the spec, information such as whether an element is deprecated or obsoleted should not be indicated by color (or background color) alone (cf. WCAG 2.0 SC 1.4.1 <https://www.w3.org/WAI/WCAG20/quickref/#visual-audio-contrast-without-color> ). 

4. Section 5.1 General. The method of associating a text profile document instance with an image profile document instance should be specified for interoperability reasons, and not be left open to the specific implementation.  Also, the association should be in both ways, i.e. also from the image profile document instance to the text profile document instance.

5. Section 6 Supported Features and Extensions. All font-related features are prohibited for the image profile. This seems to be an unnecessary restriction if the image profile contains images in SVG format which could be rendered differently based on the author’s choice of font characteristics.

6. Section 7.7.3 itts:forcedDisplay. This seems like a temporary solution. Wouldn’t it be better to define semantic layers of information that each could be made visible and invisible at runtime as appropriate for the user?  For example, the user may want to see either speech-only (subtitles), narration speech only (parts of subtitles), foreign-language speech-only (parts of subtitles) or any combination of them. 

7. Section 7.7.4 itts:altText.  While we see this feature as useful for accessibility purposes, it should be mandatory for images rather than recommended only. As mentioned in the spec, one could take the pertaining text passage from the text profile document instance – but (1) an accompanying text profile is not required, and (2) the alternative text for the image could be different from the textual caption. Therefore, the itts:altText element should always be specified, but it should be empty for decorative images (not clear if a “decorative image” used as a caption makes sense anyway). By requiring an itts:altText for every image, but allowing for an empty element in case of a decorative image, we would align it with the alt attribute in HTML5 for images.

<End Draft Comment>

*       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 23 January.

Janina
 
 APA Tracking Notes

apa-ACTION-2152:
 Assigned to: Gottfried Zimmermann
https://www.w3.org/tr/ttml-imsc1.1/

Draft comments by Gottfried:
http://lists.w3.org/Archives/Public/public-apa/2017Nov/0008.html


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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