Re: TTML2/TTML1 Backwards compatibility analysis

Hi Cyril,

> I did not see the changes in TTML2 that would affect style inheritance. I may have missed it,
> so if anyone could point to those differences, it'd be very useful.

See https://github.com/w3c/ttml1/issues/220 .

>  displayAspectRatio, but it is a new TTML2 feature, I'm assuming it was meant
> to be pixelAspectRatio. Covered in my document. Have I missed anything?

IMSC1 specifies ittp:aspectRatio [1]

[1] https://www.w3.org/TR/ttml-imsc1/#ttp-aspectRatio

Best,

-- Pierre

On Wed, Oct 18, 2017 at 1:57 PM, Cyril Concolato <cconcolato@netflix.com> wrote:
> Thank you Mike for the feedback. See my comments inline.
>
> On Wed, Oct 18, 2017 at 8:52 AM, Michael Dolan <mike@dolan.tv> wrote:
>>
>> This is definitely a good exercise – thanks Cyril.  A few comments:
>>
>> The analysis is not clear about whether it covers documents, processors
>> (in general) or presentation processors. The concern is about presentation
>> processors, which is complicated by explicit potential for variations
>> (available fonts, etc.). Some qualifications are needed of the form “all
>> allowed variations being equal”;
>
> In this exercise I was concerned with how a TTML1 document (not containing
> any TTML2 feature) would be rendered by a TTML2 presentation processor, in
> particular if the rendering would be an acceptable results according to
> TTML1. So this includes all variations allowed per TTML1.
>
>>
>> Our editor came to a different conclusion (there are compatibility issues)
>> with specific examples on a recent call, so we need to resolve that. Perhaps
>> these are captured in the orange highlight (or should I say #FFA500 ; and
>
> From the 10/12 call, I can see:
> - lineHeight. Covered in my document.
> - displayAspectRatio, but it is a new TTML2 feature, I'm assuming it was
> meant to be pixelAspectRatio. Covered in my document.
> Have I missed anything?
>
> I'm concerned about:
> - Pierre's words:
> "basic things like lineHeight style inheritance."
> I did not see the changes in TTML2 that would affect style inheritance. I
> may have missed it, so if anyone could point to those differences, it'd be
> very useful.
>
> - Glenn's words:
> "There are layers that affect every feature - it's not simple than just
> talking about
> ... individual style features."
> I'd like to understand what this means. I understand that there are general
> aspects that affect every feature (like style resolution) or relationships
> between style features (like DAR vs. PAR) but I didn't see "layers that
> affect every feature" differently between TTML1 and TTML2.
> Glenn, can you clarify? or give an example?
>
>
>> Without consensus of an explicit stated goal of presentation processor
>> backwards compatibility, it doesn’t mean it won’t break before publication
>> as a Rec or be unintentionally vague; But we can’t seem to bring ourselves
>> to make such a statement for some reason despite an agreement in principle 2
>> meetings ago to do so (and my assignment to propose TTML2 spec language).
>> But maybe this exercise will make everyone more comfortable doing that.
>
> Hopefully that should help the discussion stay focused and avoid discussing
> for hours broad statements.
>
> Regards,
> Cyril
>>
>>
>>
>> Regards,
>>
>>                Mike
>>
>>
>>
>> From: Nigel Megitt [mailto:nigel.megitt@bbc.co.uk]
>> Sent: Tuesday, October 17, 2017 10:00 AM
>> To: Cyril Concolato <cconcolato@netflix.com>; public-tt@w3.org
>> Subject: Re: TTML2/TTML1 Backwards compatibility analysis
>>
>>
>>
>> Thanks Cyril,
>>
>>
>>
>> I think it's very useful to focus on the concrete differences rather than
>> the abstract – we may find that we can resolve them.
>>
>>
>>
>> I've added this (practical compatibility issues between TTML1 and TTML2)
>> to Thursday's agenda.
>>
>>
>>
>> The URL in your email had an error in: the correct one should be
>> https://docs.google.com/document/d/1Ri7RBBsbIK9SRxA1KsHRejXbYBuL4CRRrbmEZRbwZpg/edit?usp=sharing
>>
>>
>>
>> In the meantime if everyone interested in this could look at the document
>> and comment/edit it etc that would be very helpful.
>>
>>
>>
>> Kind regards,
>>
>>
>>
>> Nigel
>>
>>
>>
>>
>>
>> From: Cyril Concolato <cconcolato@netflix.com>
>> Date: Saturday, 14 October 2017 at 01:09
>> To: "public-tt@w3.org" <public-tt@w3.org>
>> Subject: TTML2/TTML1 Backwards compatibility analysis
>> Resent-From: <public-tt@w3.org>
>> Resent-Date: Saturday, 14 October 2017 at 01:11
>>
>>
>>
>> Hi all,
>>
>>
>>
>> Following yesterday's call, I started an analysis of the possible
>> backwards compatibility issues of TTML2 vs TTML1. The results are here:
>>
>>
>> https://docs.google.com/document/d/1Ri7RBBsbIK9SRxA1KsHRejXbYBuL4CRRrbmEZRbwZpg/edit?usp=sharing
>>
>>
>>
>> This is my analysis, and it might contain errors, oversights. If it is the
>> case, feel free to comment on it.
>>
>>
>>
>> With the current status, it looks to me that there is no real backwards
>> compatibility issue, in the sense that a TTML2 processor would produce a
>> result, when processing a TTML1 document, that would be acceptable with what
>> the TTML1 spec indicates.
>>
>>
>>
>> HTH,
>>
>> Cyril
>>
>>
>>
>>
>>
>>
>>
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Received on Wednesday, 18 October 2017 21:11:38 UTC