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[Bug 27054] Accessibility Concerns

From: <bugzilla@jessica.w3.org>
Date: Thu, 30 Oct 2014 18:37:33 +0000
To: public-html-a11y@w3.org
Message-ID: <bug-27054-3290-1KuFzywPiU@http.www.w3.org/Bugs/Public/>
https://www.w3.org/Bugs/Public/show_bug.cgi?id=27054

--- Comment #7 from David Dorwin <ddorwin@google.com> ---
(In reply to Henri Sivonen from comment #6)
> (In reply to John Foliot from comment #3)
> > While I will ask an engineer more involved with the technical aspects of
> > CDMs to weigh in if I am incorrect, it is our understanding that the
> > encryption is done at the media-wrapper layer, and once the wrapper is
> > "unlocked" all of the piece-parts (including any in-band support content)
> > would be exposed to the existing APIs in exactly the same fashion as
> > unencrypted content.
> 
> This is not a correct assumption in general. EME has been designed to allow
> arrangements where the DRM subsystem performs more steps than merely
> decryption in order to hide things from the browser engine.
> 
> Note that I'm not claiming that anyone is actually planning to a) let
> caption tracks [that are actually separate tracks as opposed to being U.S.
> TV captioning-compatible data inside an MPEG-2 video track] be encrypted and
> b) not let the decrypted caption track flow into the browser engine.

Would either of you like to propose text to address these concerns? Maybe we
should file a separate sub-bug specifically for text track issues.

> (In reply to David Dorwin from comment #5)
> > EME assumes encryption is on blocks within the media container.
> 
> While this may be the assumption and what every implements in practice, is
> there actually something in the spec that prohibits the encryption being a
> wrapper around the media container? (Not that it's relevant for this
> bug--just pointing out how many things EME doesn't actually specify, AFAICT.)

Good point. What restrictions do we need to place on the media? Maybe open a
separate bug for this since it's not specifically an accessibility issue. Also,
if you find other underspecification issues, please file bugs for those too. A
number of assumptions were not clearly documented, and we've been trying to
address those.

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Received on Thursday, 30 October 2014 18:37:34 UTC

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