Re: Objections to TPAC resolutions on IMSC1.1

All,

This is a situation in which we do not currently seem to have consensus. It appears that two camps exist, with mutually incompatible visions for how the IMSC 1.1 and TTML2 specifications should incorporate some features.

Be reminded that W3C consensus means we have to find a solution that everyone can accept, even though it might not be the one that everyone thinks is the best alternative.

To summarise the technical issue as I understand it:

* IMSC 1.0.1 includes extensions not in TTML1, defined using syntax in namespaces not defined by TTML1
* We want to support the requirements met by those extensions in IMSC 1.1
* We want to support the requirements met by those extensions in TTML2
* We want IMSC 1.1 to be a subset of TTML2 – there are varying degrees of strength about this amongst the group members, i.e. some want all non-TTML2 features to be deprecated, others are happy to continue with non-deprecated extensions.
* It is important to some (maybe all) members that IMSC 1.1 processors be able to process IMSC 1.0.1 documents
* We discussed but rejected creating an IMSC 2 that is a pure subset of TTML2 and does not natively support IMSC 1.0.1
* It is important to some (but not all) members that TTML2 defines all features in its own namespace
* The idea of adopting extensions into TTML2 and making them features with no change to their existing namespace was discussed but not adopted. There was a formal objection on the grounds that all TTML features must be defined in the TTML namespace. There was also a process point that we would need to seek permission from EBU for inclusion of EBU namespace extensions.

During the TPAC 2017 face to face meeting (minutes<https://www.w3.org/2017/11/09-tt-minutes.html>) we resolved one of two approaches for each feature:

1. In TTML2: include a new feature in a TTML namespace. In IMSC 1.1: deprecate the IMSC 1.0.1 extension AND include the TTML2 feature AND provide a mapping from the deprecated extension to the new feature.
2. In TTML2: do not include a new feature. In IMSC 1.1: include the IMSC 1.0.1 extension.

Netflix has objected to some of those resolutions within the WG's review period defined under the Decision Policy in the Charter. I have received no other objections within that period (which expires at the end of the working day today, California time). I have updated and where necessary reopened the relevant GitHub issues indicating the objection.

* The idea of synonyms or aliases was raised (disclosure: by me), discussed but not adopted, i.e. TTML namespace syntax for features where each feature is a functional equivalent or superset of an IMSC 1.0.1 extension, and both may be supported in IMSC 1.1 with a mapping to the canonical TTML2 equivalent. The synonym may additionally be noted informatively in TTML2. The key negative point was that it would encourage the use of both sets of syntax in many documents with no clear end point to the practice and no practical benefit. However I cannot recall any formal objection, nor find one in the minutes.

The Netflix objection essentially requests that this latter model be adopted, whilst deprecating the IMSC 1.0.1 extensions.

Given that I cannot recall any formal objection to the synonym/alias proposal requested by Netflix, I'd like to check if we actually have consensus to adopt it already, i.e. if despite it not being everyone's favourite option, it is something that everyone can nevertheless live with.

Does anyone object to any of the Netflix proposals? If so, please be specific about the nature of the objection. This will help us to construct new proposals.

This topic will be on the agenda for next week's call (November 30th), but if possible I would like to have a sense of the conclusion or any as yet unraised concerns before the meeting. If anyone would like a call with me or others to discuss this informally ahead of the meeting, I am happy to support that, and can be available on Monday 1600-1700 UK time, Tuesday 1630-1730 UK time or Wednesday 1500-1730 UK time.

Nigel


From: Cyril Concolato <cconcolato@netflix.com<mailto:cconcolato@netflix.com>>
Date: Wednesday, 15 November 2017 at 18:55
To: TTWG <public-tt@w3.org<mailto:public-tt@w3.org>>
Subject: Objections to TPAC resolutions on IMSC1.1
Resent-From: <public-tt@w3.org<mailto:public-tt@w3.org>>
Resent-Date: Wednesday, 15 November 2017 at 18:56


Dear TTWG experts,


Following TPAC, Netflix would like to inform the group that it is not satisfied with some of the resolutions regarding IMSC1.1 and objects to them. Netflix thinks that two important goals must be satisfied in defining TTML2 and IMSC1.1:

- IMSC1.1 must be a strict-subset of TTML2, aside from deprecated features. We believe it is bad practice for W3C to define two TTML-based standards, at the same time, which are not compatible with each other.

- TTML2 must limit its normative references to Web Platform standards. We believe it is bad practice to have to compile multiple sources of information outside of the Web Platform to implement the standard.


Netflix asks for the following actions:

a) Marking ittp:activeArea deprecated in IMSC1.1, using a reference to IMSC1.0.1 and no definition in IMSC1.1, in favor of ttp:activeArea, restricted to using two-component values such that ttp:activeArea can be used to do no more than IMSC1.0.1 ittp:activeArea.

b) Marking ittp:aspectRatio deprecated in IMSC1.1, using a reference to IMSC1.0.1 and no definition in IMSC1.1, in favor of ttp:displayAspectRatio. There does not seem to be a need for restricting ttp:displayAspectRatio.

c) Marking itts:forcedDisplay deprecated in IMSC1.1, using a reference to IMSC1.0.1 and no definition in IMSC1.1, in favor of a combination of 'condition' and 'tts:visibility', with the appropriate restrictions on condition such that it remains simple to implement, while at the same time offering more flexibility than forcedDisplay.

d) Adding the definitions of itts:fillLineGap, ebutts:linePadding and ebutts:multiRowAlign to TTML2, with no change to the semantics, but in the TTML namespace; and marking the itts/ebutts version as deprecated in IMSC1.1.

e) IMSC1.1 should indicate that when TTML2 features are used in the same document at the same time as their non-TTML2 equivalent and deprecated features, the TTML2 features prevail. This insures that future versions of IMSC can effectively remove the features marked as deprecated.


Netflix believes that this approach provides clearly designed, forward looking standards, reducing the complexity of the TTML ecosystem.


Netflix is aware that this requires an effort of the TTML community as follows:

- IMSC1.0.1 renderers do not need to be updated, unless they need to support Japanese features. The changes required by the proposed dual syntax and deprecation model are minor compared to them, as they can be implemented using aliases or simple transforms.

- Authoring tools already supporting IMSC1.0.1 do not need to migrate to the TTML2 syntax, as renderers are required to support both. They only need to be updated to support Japanese features. They would need to be updated when the deprecated features are removed in a future version.

- Specs need to be updated. Netflix is willing to update the TTML2 and IMSC1.1 specs as proposed above.

- Test suites need to be updated. For each of the features above, 2 additional tests need to be provided: one with the TTML2 flavor and without the IMSC1.0.1 flavor; and one with both (testing the override model). Netflix is willing to contribute these tests.


We suggest adding these points to the next meeting's agenda.


Best regards,

Cyril