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

On Thu, Sep 25, 2014 at 3:38 AM, 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?
>

The TTML to ISD conversion process will normatively use this parameter. It
is also used by the proposed CP5 for conversion to HTML.


>
> 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.
>

We have an interesting issue here: what are authors using for the origin of
document times. SMIL assumes they are relative to beginning of related
media. However, apparently SMPTE time base authors have been using the
origin of the time line of related meda. But this is unrelated to
ttp:mediaDuration.


>
> 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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