RE: Timed tracks

I don’t see that burning the captions into the video is required, and as John says that prevents AT from accessing the text. Browsers are capable of setting up walls for things like iframes; that is the level of protection that is required.

Given that the page author will have access to the video timeline, they will of course be able to superimpose anything they like; and turning on and off the caption stream is fine. What I want to avoid is inadvertent leakage, especially when they come from different source to the HTML.

Explicit control through something like a pseudo element to set the baseline styles in the captions could be reasonable, since the captions would have the option of overriding that. TTML is fairly well set up to support something like that.

From: rocallahan@gmail.com [mailto:rocallahan@gmail.com] On Behalf Of Robert O'Callahan
Sent: Friday, April 23, 2010 5:49 AM
To: John Foliot
Cc: Sean Hayes; Philippe Le Hegaret; Ian Hickson; public-html@w3.org
Subject: Re: Timed tracks

On Fri, Apr 23, 2010 at 4:25 PM, John Foliot <jfoliot@stanford.edu<mailto:jfoliot@stanford.edu>> wrote:
Robert O'Callahan wrote:
> Burning captions into the video stream is the most
> effective way to achieve that goal, and even that
> isn't foolproof.
Robert, when you say "burned in" are you referring to time-stamp text files
included in the media wrapper, of converted to a binary format (.scc) and
merged with the video asset as pixel data?  If it is the later, it makes it
impossible to repurpose that text to AT like screen readers and Braille
refresh bars.

Yes, the latter. I agree it's not desirable. However, it's the best way to achieve Sean's goal of not allowing an HTML page author to "undermine" the captions. Personally I think that shouldn't be a goal...

Rob
--
"He was pierced for our transgressions, he was crushed for our iniquities; the punishment that brought us peace was upon him, and by his wounds we are healed. We all, like sheep, have gone astray, each of us has turned to his own way; and the LORD has laid on him the iniquity of us all." [Isaiah 53:5-6]