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

Hi Nigel,

My input.

>that the test for earlier and
> later is not precisely enough defined.
> Do you mean to compare the byte locations of the opening tag of the elements in the flattened document structure, for example?

Sure. I am not convinced we need to be this specific. AFAIK the only
means in TTML for a first element to 'reference' a second element is
using xml:id, and a <p> cannot contain another <p>.

Please propose specific text if you are not happy with the current text.

> It is also unclear in the new wording (list item 2) how an ISD ³maps² to a
> content element.

What about:

"""
given two Intermediate Synchronic Documents A and B with presentation
times TA and TB, respectively, TA is not greater than TB if A includes
a p element that occurs earlier in the document than any p element
that B includes;
"""

>Did the 3rd ISD above 'map' to p2?

No.

Thanks,

-- Pierre



On Wed, Aug 13, 2014 at 11:35 AM, Nigel Megitt <nigel.megitt@bbc.co.uk> wrote:
> Hi Pierre,
>
> I¹ve added a note to ISSUE-330, quoted here for convenience:
>
> The updated text uses phrases such as Œearlier/later in the document¹ -
> this does not address my original concern, that the test for earlier and
> later is not precisely enough defined. Do you mean to compare the byte
> locations of the opening tag of the elements in the flattened document
> structure, for example?
>
> It is also unclear in the new wording (list item 2) how an ISD ³maps² to a
> content element. An ISD is typically constructed from multiple elements
> simultaneously. There seems to be an assumption that an ISD can only
> relate to a single p, which is such a significant constraint that I wonder
> if it was intended.
>
> Take this example:
>
> <p id="p1" begin="00:01:00" end="00:02:00">
> [some stuff]
> </p>
> <p id="p2" begin="00:01:30" end="00:01:45">
> [some other stuff]
> </p>
>
> We have here the following ISDs:
> 1. 00:01:00 containing p1
> 2. 00:01:30 containing p1 and p2
> 3. 00:01.45 containing p1
> 4. 00:02:00 containing nothing
>
> Is this progressively decodable? Did the 3rd ISD above 'map' to p2? It
> doesn't itself contain p2: it simply has its timing derived from p2.
>
>
> Kind regards,
>
>
> Nigel

On Tue, Aug 12, 2014 at 5:02 PM, Pierre-Anthony Lemieux
<pal@sandflow.com> wrote:
> 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 Wednesday, 13 August 2014 11:57:04 UTC