Re: Formal Object to any new CR of IMSC1

On Fri, Dec 11, 2015 at 2:51 AM, Nigel Megitt <>

> Glenn,
> I do not think this is a helpful move.
> To recap the GitHub issue discussion:
> Since IMSC defines two profiles of TTML the normative fallback defined in
> TTML1 applies in the absence of any other defined behaviour.

That won't work, since in the EBU-TT-D case, it would be wrong to apply the
DFXP Transformation Profile.

> Furthermore the mechanisms for specifying either of the two profiles are
> coincident with the ttp:profile attribute as defined in TTML 1 and the
> presence  of ebuttm:conformsToStandard with the appropriate value for
> EBU-TT-D also indicates IMSC text profile conformance.
> So this objection does not appear to be well formed, in that the assertion
> that no fallback behaviour is defined is false.

Clearly by "no fallback" I mean no fallback that yields an IMSC profile. So
in that sense my point stands.

> At the very least, IMSC is no worse than TTML1 in this respect, a topic
> which was much discussed at our recent face to face meeting.

Without a determination of IMSC profile that yields either text or image
profile, it is not possible to process a document that purports to be an
IMSC conforming document since processor conformance is defined in terms of
knowledge of the applicable profile.

> Finally, it is clear that we do not have consensus for an IMSC specific
> algorithm, which by the way would further fragment the processing of
> generic TTML documents since any such processor would have to be configured
> somehow to expect one of either TTML or IMSC to know which rules to use. It
> is clear that IMSC is intended to be a profile of TTML and not a separate
> format in its own right.

But that [any such processor would have to be configured somehow to expect
one of either TTML or IMSC to know which rules to use] is manifestly true
already, with or without an IMSC specific algorithm.

> I hope these arguments will persuade you to consider other options.

>From my perspective, both you and Pierre are not attempting to address my
comment substantively. I have proposed one possible fallback algorithm, I'm
willing to entertain other algorithms as long as they produce one of two
answers: IMSC text or IMSC image profile and do not require pre-parsing the
entire document.

Until that occurs, my objection stands.

> Kind regards
> Nigel
> > On 11 Dec 2015, at 00:37, Glenn Adams <> wrote:
> >
> > Unless and until a fallback profile is mandated normatively in IMSC1,
> SKYNAV formally objects to any new CR being published.
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Received on Friday, 11 December 2015 16:04:15 UTC