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Media Requirements--Sec. 2.8 Sign Translation

From: John Foliot <jfoliot@stanford.edu>
Date: Wed, 30 Jun 2010 14:27:34 -0700 (PDT)
To: "'HTML Accessibility Task Force'" <public-html-a11y@w3.org>
Message-ID: <008501cb189b$0e290d40$2a7b27c0$@edu>
Sign Translation (6 comments)




Q: Decoding and rendering multiple streams is even more difficult with
video than with audio. Video decoding hardware used in many mobile devices
is not able to decode more than one video stream simultaneously.

A: Make this requirement a SHOULD requirement for browsers.  Strong
authoring guidance for content creator will mitigate situations where
user-agents are unable to support multiple video streams (WCAG) - for
example, on mobile devices that cannot support multiple streams, authors
should be encouraged to offer 2 versions of the media stream, including
one with signed captions burned into the media

Comment: describe better the two cases: of picture in picture (where the
background portion of the sign video is visible to the user), and alpha
blended; where only the signer and no background is mixed onto the main
video. Note that SL could also be in a separate window frame to the main
video (main video for example being resized, this is sometimes done in TV


(SL-1) Support sign language video either as a track as part of a media
resource or as an external file. 

Q: I think you need to support multiple tracks for different sign
languages if they are available and allow the user to specify which one is

A: this would be addressed using <trackgroup>, as it is done for multiple
languages for captions


(SL-2) Support the synchronized playback of the sign language video with
the media resource.


(SL-3) Support the display of sign language video either as
picture-in-picture or alpha-blended overlay, as parallel video, or as the
main video with the original video as picture-in-picture or alpha-blended

Q:  (SL-3) What is "as parallel video"? "as picture-in-picture or
alpha-blended overlay" and "as the main video with the original video as
picture-in-picture or alpha-blended overlay" also seem to mean exactly the
same thing, am I missing something?

A: Either: 2 videos are played in synch, and placement (including
alpha-blends) is handled by CSS. Parrallel video means 2 discrete videos
playing in synch with each other (

Q: Note that <track> may not be the solution for this, rather linking
several <video> elements together seems like a more reasonable solution if
the video tracks are from separate resources.

A: It is preferable to have one discrete <video> element contain all
pieces for synch purposes


(SL-4) Support multiple sign language tracks in several sign languages. 

(SL-5) Support the interactive activation/deactivation of a sign language
track by the user.


John Foliot / Eric Carlson
Received on Wednesday, 30 June 2010 21:28:09 UTC

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