ISSUE-338: inconsistent implicit duration of singleton span in sequential container

inconsistent implicit duration of singleton span in sequential container

State:
OPEN
Product:
TTML 1.0
Raised by:
Glenn Adams
Opened on:
2014-08-26
Description:
The implicit duration of an anonymous span child of a sequential container is explicitly defined to be zero (section 10.4); however, the implicit duration of an explicit singleton (i.e., non-nested) span in the same context

Here is an example, where I ignore whitespace to aid in viewing. Given a fragment:

<p timeContainer="seq">
Foo
<span>Bar</span>
Baz
</p>

Generating anonymous spans to wrap text nodes:

<p timeContainer="seq">
<span xml:id="anon1">Foo</span>
<span>
<span xml:id="anon2">Bar</span>
</span>
<span xml:id="anon3">Baz</span>
</p>

Applying timing semantics as presently defined to resolve implicit duration:

<p timeContainer="seq" durImplicit="indefinite">
<span xml:id="anon1" durImplicit="0">Foo</span>
<span durImplicit="indefinite">
<span xml:id="anon2" durImplicit="indefinite">Bar</span>
</span>
<span xml:id="anon3" durImplicit="0">Baz</span>
</p>

Here, anon2 is assigned an indefinite implicit duration because its parent is an explicit span which defaults to 'par' time containment semantics. Since SMIL requires a seq container that contains an indefinite duration child to also be indefinite, then that indefinite propagates up the node tree.

This seems counterintuitive. I propose to resolve by a slight change in 10.4 from the current text:

"if the anonymous span's parent time container is a parallel time container, then the implicit duration is equivalent to the indefinite duration value as defined by [SMIL 2.1]; if the anonymous span's parent time container is a sequential time container, then the implicit duration is equivalent to zero"

to read:

"if the anonymous span's nearest explicit time container ancestor is a sequential time container, then the implicit duration is equivalent to zero; otherwise, it is equivalent to the indefinite duration value as defined by [SMIL 2.1]"

and add the following Note

"Note: An element is an explicit time container if it specifies a timeContainer attribute."

Reworking the above example with the new text, we get:

<p timeContainer="seq" durImplicit="0">
<span xml:id="anon1" durImplicit="0">Foo</span>
<span durImplicit="0">
<span xml:id="anon2" durImplicit="0">Bar</span>
</span>
<span xml:id="anon3" durImplicit="0">Baz</span>
</p>

The resolution of this issue also needs applied to TTML2.
Related Actions Items:
No related actions
Related emails:
  1. {agenda} TTWG Meeting 4/9/2014 (from nigel.megitt@bbc.co.uk on 2014-09-03)
  2. ISSUE-338: inconsistent implicit duration of singleton span in sequential container [TTML 1.0] (from sysbot+tracker@w3.org on 2014-08-26)

Related notes:

Continuing the first sentence of the description:

"... is assigned indefinite, an apparent inconsistency."

Glenn Adams, 26 Aug 2014, 17:57:40

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David Singer <singer@apple.com>, Nigel Megitt <nigel.megitt@bbc.co.uk>, Chairs, Thierry Michel <tmichel@w3.org>, Philippe Le H├ęgaret <plh@w3.org>, Staff Contacts
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