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Re: ISSUE-319 (HRM should be a processor compliance test): HRM should be a processor compliance test and allow different levels of complexity for different use cases [TTML IMSC 1.0]

From: Pierre-Anthony Lemieux <pal@sandflow.com>
Date: Fri, 23 May 2014 08:56:32 -0700
Message-ID: <CAF_7JxCLY4tt6ZKDE_-2yDNCcjbyuZ3rUBg0ByoZ=7mS+E51RA@mail.gmail.com>
To: Nigel Megitt <nigel.megitt@bbc.co.uk>
Cc: Timed Text Working Group <public-tt@w3.org>
Hi Nigel,

> so that it can be used to construct maximally complex test documents that compliant
> processors must be able to process successfully, while permitting processors
> to process even more complex documents.

I am not aware of provisions in the specification that prevent
processors from implementing capabilities beyond that required to
process documents that conform to (proposed) IMSC 1.0.

> > This would open up the possibility for future increases in complexity
> by allowing the threshold values for sub-profiles of IMSC to be changed
> to 'greater complexity', in the knowledge that pre-existing IMSC compliant
> documents will be continue to be processable.

Yes. That option exists in my mind.

> Very closely related to this, the HRM (§7) [1] in various places sets threshold
> parameter values using the wording "Unless specified otherwise, the following table
> shall specify..." but there is no mechanism for specifying otherwise

As it stands, the mechanism to specify otherwise would be in a
different specification. In other words, anyone in the world could
write a specification referencing IMSC 1.0 and including a provision
such as "the Normalized image copy performance factor (ICpy) shall be
12".

Would clarifying this in the specification make sense?

> It should be permitted for processors not to be subject to the HRM values at all,

Processors are not subject to HRM constraints, IMSC 1.0 documents are.
As suggested above, processors can choose to implement abilities that
go beyond that required to process IMSC 1.0 documents, e.g. to process
other profiles, including profiles that extend IMSC 1.0.

Best,

-- Pierre


On Fri, May 23, 2014 at 5:54 AM, Timed Text Working Group Issue
Tracker <sysbot+tracker@w3.org> wrote:
> ISSUE-319 (HRM should be a processor compliance test): HRM should be a processor compliance test and allow different levels of complexity for different use cases [TTML IMSC 1.0]
>
> http://www.w3.org/AudioVideo/TT/tracker/issues/319
>
> Raised by: Nigel Megitt
> On product: TTML IMSC 1.0
>
> The Hypothetical Render Model is defined as a content profile constraint, which appears to set a maximum complexity on all documents. It would be better to make it a minimal processor profile constraint, i.e. so that it can be used to construct maximally complex test documents that compliant processors must be able to process successfully, while permitting processors to process even more complex documents.
>
> This would open up the possibility for future increases in complexity by allowing the threshold values for sub-profiles of IMSC to be changed to 'greater complexity', in the knowledge that pre-existing IMSC compliant documents will be continue to be processable.
>
> Very closely related to this, the HRM (§7) [1] in various places sets threshold parameter values using the wording "Unless specified otherwise, the following table shall specify..." but there is no mechanism for specifying otherwise; §4.7 simply states that all sequences "of intermediate synchronic documents SHALL be reproducible..." without providing any reference to an external location where the parameters in the HRM can be set to other values.
>
> One possible solution to this is to introduce a 'complexity level' table and list the current parameter values as, for example 'complexity level 1' and change the wording in §4.7 to state that for use cases that need to specify complexity they must either specify an equivalent table with alternative parameter values or use the default 'level 1' values. It should be permitted for processors not to be subject to the HRM values at all, and there should be scope in future versions of IMSC to add more levels, if there is a strong argument for doing so.
>
> [1] http://www.w3.org/TR/ttml-imsc1/#hypothetical-render-model
>
>
>
Received on Friday, 23 May 2014 15:57:24 UTC

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