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Re: ISSUE-346: Need ttp:mediaDuration parameter [TTML2]

From: Glenn Adams <glenn@skynav.com>
Date: Thu, 25 Sep 2014 07:15:43 -0600
Message-ID: <CACQ=j+eE_ian3UiAw1qkEPvdHDqT_KnDm8qzs1y0w=s-HGCqgg@mail.gmail.com>
To: Nigel Megitt <nigel.megitt@bbc.co.uk>
Cc: John Birch <John.Birch@screensystems.tv>, Timed Text Working Group <public-tt@w3.org>
On Thu, Sep 25, 2014 at 4:11 AM, Nigel Megitt <nigel.megitt@bbc.co.uk>
wrote:

> No processing requirements that use ttp:mediaDuration are stated either in
> the ttp:mediaDuration section at [1]  or anywhere else in the document,
> right now.


Be patient, it will be.


> Taken in isolation this would suggest that it is metadata and
> should not be in the parameter namespace, however I think it is merely a
> reflection of work in progress.
>
> [1]
> https://dvcs.w3.org/hg/ttml/raw-file/default/ttml2/spec/ttml2.html#paramete
> r-attribute-mediaDuration
>
> My expectation is that, regardless of how they are calculated, the
> effective media begin time and media end time will be used to define the
> temporal period within which any ISDs should be created for display
> alongside the related media, and that mediaDuration would therefore be
> referenced in the Intermediate Synchronic Document Construction process at
> [2]. There's an editorial note on that section - possibly when that note
> has been resolved into spec text this will become clearer.
>
> [2]
> https://dvcs.w3.org/hg/ttml/raw-file/default/ttml2/spec/ttml2.html#semantic
> s-region-layout-step-1
>
> I've proposed in the "Issue-270 and Issue-335" thread that starts at [3]
> that this period might better be defined explicitly in terms of mediaBegin
> and mediaEnd parameters expressed in the time base of the document. If
> mediaDuration is needed and the time base and marker modes permit time
> calculations (e.g. it is not SMPTE - discontinuous) then it can be
> calculated as (mediaEnd - mediaBegin).
>
> [3] http://lists.w3.org/Archives/Public/public-tt/2014Sep/0065.html
>
>
> I'm interested in the requirement/use case though: when you say "allows
> time values within a document to be 'offset' relative to the start of
> associated media", what calculations are you envisaging that a processor
> should perform, exactly, and in what circumstances might they be useful?
>
>
> Kind regards,
>
> Nigel
>
>
> On 25/09/2014 10:38, "John Birch" <John.Birch@screensystems.tv> wrote:
>
> >I am uncertain about the 'requirement' for a duration parameter?
> >What is the current situation... does TTML1 work as if the media duration
> >is 'indefinite' ?
> >In which case what additional benefit does having a defined duration
> >bring?
> >
> >Of far more importance (IMHO) is a media start value - that allows time
> >values within a document to be 'offset' relative to the start of
> >associated media.
> >
> >Best regards,
> >John
> >
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> >P Before printing, think about the environment-----Original Message-----
> >From: Timed Text Working Group Issue Tracker
> >[mailto:sysbot+tracker@w3.org]
> >Sent: 21 September 2014 13:35
> >To: public-tt@w3.org
> >Subject: ISSUE-346: Need ttp:mediaDuration parameter [TTML2]
> >
> >ISSUE-346: Need ttp:mediaDuration parameter [TTML2]
> >
> >http://www.w3.org/AudioVideo/TT/tracker/issues/346
> >
> >Raised by: Glenn Adams
> >On product: TTML2
> >
> >In order to perform ISD processing, it is necessary to know the duration
> >of root external extent. When associate with a related media object, this
> >is the simple duration of the related media object. If this is known at
> >authoring time, then it is an important parameter that should be
> >specified. I propose defining a ttp:mediaDuration parameter attribute
> >that takes either an offset-time form of a time expression or the keyword
> >"indefinite", where the latter is used (or implied) when no related media
> >object exists or its simple duration is unknown or indefinite. If this
> >parameter is not specified, then it would be treated as if indefinite
> >were specified.
> >
> >
> >
> >
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Received on Thursday, 25 September 2014 13:16:29 UTC

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