RE: TTML2/TTML1 Backwards compatibility analysis

This is definitely a good exercise – thanks Cyril.  A few comments:


  1.  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”;
  2.  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
  3.  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.

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<mailto:cconcolato@netflix.com>>
Date: Saturday, 14 October 2017 at 01:09
To: "public-tt@w3.org<mailto:public-tt@w3.org>" <public-tt@w3.org<mailto:public-tt@w3.org>>
Subject: TTML2/TTML1 Backwards compatibility analysis
Resent-From: <public-tt@w3.org<mailto: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<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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