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Objections to TPAC resolutions on IMSC1.1

From: Cyril Concolato <cconcolato@netflix.com>
Date: Wed, 15 Nov 2017 10:55:36 -0800
Message-ID: <CAMiyXwBwub6PJ7yd8aoQECNe1wftTaKM7MGg3b-winFCkNyGeQ@mail.gmail.com>
To: TTWG <public-tt@w3.org>
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

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

- 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,

Received on Wednesday, 15 November 2017 18:56:00 UTC

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