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AW: Call for Consensus (CfC): APA Comment on Media Hints

From: Gottfried Zimmermann \(Lists\) <zimmermann@accesstechnologiesgroup.com>
Date: Wed, 7 Jul 2021 17:30:12 +0200
To: "'Janina Sajka'" <janina@rednote.net>, "'Accessible Platform Architectures Administration'" <public-apa-admin@w3.org>
Message-ID: <0c3301d77344$fa92bd10$efb83730$@accesstechnologiesgroup.com>

Best regards,

-----Ursprüngliche Nachricht-----
Von: Janina Sajka (janina@rednote.net) <janina@rednote.net> 
Gesendet: Dienstag, 6. Juli 2021 21:12
An: Accessible Platform Architectures Administration
Betreff: Call for Consensus (CfC): APA Comment on Media Hints


This is a Call for Consensus (CfC) to the Accessible Platform
Architectures (APA) Working Group testing whether we have group
consensus on comments and suggested edits on the MediaStreamTrack
Content Hints draft specification, at

<beginning of suggested comment>


APA comments on the MediaStreamTrack Content Hints draft specification, at


*Content hint attributes defined in this specification will benefit
consumers who rely on assistive technology (AT) and personalization. *The
specification notes its focus on end-users' experience: "Adding a media
-content hint provides a way for a web application to help track consumers
make more informed decision[s]...." Content authors can author contentHint
 with the experience of AT users in mind, or UAs acting on behalf of
users.  This specification's introduction would be a good place to
clarify this as a further benefit of content hints. Content authors may
author content hints with AT in mind. In addition, we encourage User Agents
to make this hint available to downstream consumers via API,

*The specification make no mention of hints regarding support files
audio descriptions) that often accompany media content, either linked to it
in HTML externally (using the <track> element) or furnished 'in-band',
e.g., contained within the .MP4 wrapper (HasCaptions: T/F,
HasAudioDescription: T/F). If either return True, THEN they need to be
exposed in the UI: essentially as 'active' buttons in the Controls. Such
support files can be critical to the accessibility of a media track, as for
example when an American Sign Language video is supplied seperately, but
linked. Did the WG consider whether hints could also usefully convey
whether the media content has such supporting files?

Regarding Section 4: *The specification's hints could address more directly
some common **audio and video formats that are often encountered with
content that has been made accessible. *For clarity, such formats could
propose hints such as these (these are examples for clarity only, we leave
you to define such hints):

*For Audio, an additional hint to indicate the presence of
audio-description *(or some similar label as you find appropriate).
Audio-description is audio that resembles speech-recognition, but does not
contain data for the purpose of speech recognition by a machine.
Audio-description is audio that resembles "speech" but it will likely not
be appropriate to apply noise suppression or boost intelligibility of the
incoming signal.

In the language of the specification (4.1) , "A track with content
hint "audio-description"
should be treated as if it contains audio data, without background noise,
describing in words the activity in the video."

*For Video, an additional hint to indicate the presence of transcription
embedded in the video*, e.g., motion-with-transcription (or some similar
label as you find appropriate). motion-with-transcription would refer to a
motion video that has, embedded, transcription data, either a
picture-in-picture showing a sign language interpreter, or text captions
embedded in the video.

In the language of the specification (4.2): A content hint of
motion-with-transcription should be treated such that one region of the
video frame has details that are extra important, and in that region that
significant sharp edges and areas of consistent color can occur frequently
(the area with sign language interpretation, or the area with onscreen
captioned text). This screen region would optimize for detail in the
resulting individual frames rather than smooth playback. Artefacts from
quantization or downscaling should be avoided.

*Regarding section 5, the degradation preference does not address regions.*
Picture regions may be very significant for accessibility. Consider a video
with sign language interpretation embedded (e.g., in the upper right
corner), or a video with captions "burned-in" or embedded (e.g., in the
bottom of the picture area). (While APA does not advocate for such embedded
captions, they are common particularly on social media where the default
user behavior is audio "off." These regions would benefit from different
encoding decisions than the rest of the frame.  Regions may be encoded and
decoded quite differently: for example in AVC, "it is also possible to
create truly lossless-coded regions within lossy-coded pictures." *We would
find it useful and supportive of accessible content to make this
information available as an RTCDegradationPreference.*

Lastly, how are these hints communicated? We note that MP4 files can
contain metadata as defined by the format standard, and in addition, can
contain Extensible Metadata Platform (XMP) metadata. (source::


Correct these two typos:

   - Abstract: change "make more informed decision" to either "make a more
   informed decision" or "make more informed decisions"
   - Section 2. change "they appear" to "it appears"

Add to the introduction that content hint attributes defined in this
specification will benefit consumers who rely on assistive technology (AT)
and personalization.

The WG to ensure that the specification covers use cases with support
files, and that hints can be provided for those files.

In section 4, ensure that hints support the use-cases mentioned above.

In section 5.2 ensure that the specification supports regions particularly
when such regions are important for accessibility.

   <end suggested 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, Wednesday 14 July.

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


We thank Lionel Wolberger for reviewing this specification on our behalf
and for helping lead our teleconference discussions on this

Janina and Becky


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, 7 July 2021 15:37:26 UTC

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