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Re: ISSUE-310 (progressivelyDecodable needs hierarchical definition): Forward reference rule doesn't take into account child elements [TTML IMSC 1.0]

From: Pierre-Anthony Lemieux <pal@sandflow.com>
Date: Tue, 12 Aug 2014 17:02:56 +0200
Message-ID: <CAF_7JxCg284mE7N7dFHcG2rUrrj+qD=T5t0rnmk1uAtzAwQ1yw@mail.gmail.com>
To: Timed Text Working Group <public-tt@w3.org>
Addressed at https://dvcs.w3.org/hg/ttml/rev/80f2493f9079

Best,

-- Pierre

On Wed, May 21, 2014 at 1:10 PM, Timed Text Working Group Issue
Tracker <sysbot+tracker@w3.org> wrote:
> ISSUE-310 (progressivelyDecodable needs hierarchical definition): Forward reference rule doesn't take into account child elements [TTML IMSC 1.0]
>
> http://www.w3.org/AudioVideo/TT/tracker/issues/310
>
> Raised by: Nigel Megitt
> On product: TTML IMSC 1.0
>
> The definition of ttp:progressivelyDecodable [1] could be interpreted as describing an impossible scenario as it requires that no element references another element occurring later in the document. It does not define "later" to mean 'after the close tag'.
>
> Since the computed time for a content element may depend on the computed times of its children, and those children are defined later (bytewise) in the document than the opening tag this possibly unintended interpretation would result in all documents being invalid if progressivelyDecodable is "true".
>
> However, if the "after the close tag" clarification is added then the concept becomes meaningless because validation would require waiting until </body> which would negate the utility of the attribute. Something needs to be added that references the hierarchical structure of the document when interpreting this attribute.
>
> Incidentally there is also a typo somewhere because the attribute is described alternately as being in ttp: namespace and imsc: namespace, and both shouldn't be true.
>
> [1] http://www.w3.org/TR/ttml-imsc1/#ttp-progressivelyDecodable
>
>
>
Received on Tuesday, 12 August 2014 15:03:49 UTC

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