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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: Nigel Megitt <nigel.megitt@bbc.co.uk>
Date: Fri, 23 May 2014 16:30:54 +0000
To: Pierre-Anthony Lemieux <pal@sandflow.com>
CC: Timed Text Working Group <public-tt@w3.org>
Message-ID: <CFA532A5.1E488%nigel.megitt@bbc.co.uk>
Hi Pierre,

On 23/05/2014 16:56, "Pierre-Anthony Lemieux" <pal@sandflow.com> wrote:

>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.

Agreed.

>
>> > 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.

I suppose this is a matter of perspective - I see what you mean that you
could create a new 'super-profile' that has higher value complexity
parameters, and existing IMSC documents would conform to it. It just seems
a lot of effort to go to just to be able to draw glyphs on the screen more
quickly, when the rest of the document structure is identical.

>>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?

Yes it would - actually I'd like a more open mechanism to specify
alternate sets of values but this would help too.

>
>> 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.

Understood - I meant this in the context of a minimal processor profile
not as written in the current working draft.

Kind regards,

Nigel

>
>
>
>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
>>
>>
>>



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Received on Friday, 23 May 2014 16:31:25 UTC

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