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My ACTION-2080 - Review EME Section 8.5 Supported Media

From: John Foliot <john.foliot@deque.com>
Date: Wed, 24 Aug 2016 09:34:30 -0500
Message-ID: <CAKdCpxyN+d_K+RvGhMsYL60dd3u4y-8rp3J9KU2WBBRD=fUAqQ@mail.gmail.com>
To: W3C WAI Accessible Platform Architectures <public-apa@w3.org>
Colleagues,

I have reviewed the referenced section of the EME CR document here:
https://www.w3.org/TR/encrypted-media/#media-requirements

Conclusion: there does not appear to be any accessibility issues with the
EME spec and access to content such as captions, video descriptions or
similar support materials.

*******************
Section 8.5.1: Unencrypted Container - contains a MUST NOT requirement that
states that the video wrapper format (for example .mp4) MUST NOT be
encrypted, and that only the encoded video (in, for example the h.264
codec) be encrypted, which is then contained within the media wrapper. For
in-band captions (etc.) they would be transported within the unencrypted
wrapper, so here there is no actual issue: the end-user system can access
the caption file from the media wrapper.

Section 8.5.2: Interoperably Encrypted - contains a MUST statement that
insists that *IF* additional content contained within the media wrapper
requires encryption, that it uses the same encryption scheme as the video
asset. Thus, when the authenticated user is decrypting their video stream,
the decryption of the support materials would ostensibly happen at the same
time, using the same key and CDM.

Finally, Section 8.5.3: Unencrypted In-band Support Content - contains a
SHOULD NOT requirement that states (direct quote): "In-band support
content, such as captions, described audio, and transcripts, SHOULD NOT be
encrypted."

This section further contains a MUST requirement (again, directly quoted):
"Implementations that choose to support encrypted support content MUST
provide the decrypted data to the user agent to be processed in the same
way as equivalent unencrypted timed text tracks."


It is my observation and opinion that the EME Task Force have addressed the
concerns the HTML5 Accessibility Task Force raised in the face-to-face
meetings we had with them in 2013 (
https://www.w3.org/2013/04/23-html-wg-minutes.html#item12)

This closes my ACTION 2080

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

Advancing the mission of digital accessibility and inclusion
Received on Wednesday, 24 August 2016 14:34:59 UTC

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