ISSUE-263: profile feature set may not match intended feature constraints

profile feature set may not match intended feature constraints

State:
CLOSED
Product:
TTML2
Raised by:
Glenn Adams
Opened on:
2013-07-17
Description:
SDP-US makes use of the profile mechanism to define the presentation processor feature set. Section 3 says: "A TTML presentation processor conforms to this profile if it: 1.implements support for the profile definition specified in [Section 9] Features in TTML 1.0 Used in This Profile; and ...". Section 9 contains a TTML profile document. However, many of the TTML features require support for details that appear to be intended to be constrained out in the prose.

For example, Section 5.2 says: "R0013 - A document must not contain a <color> expression value used with the tts:color attribute that does not conform to the #rrggbbaa expression format as defined by [TTML10], Section 8.3.2.". Since this is clearly a document constraint, this is not technically inconsistent with the profile requirement for full support of all tts:color value expressions in the presentation processor as required by #color. However, during the development of SDP-US these document constraints were intended to simplify decoder design. If that is true then referencing #color is an error and a new TTML profile feature or a new SDP-US profile extension must be defined to define the SDP-US specific constraints for tts:color.

If that is not true (the constraints are intended to apply only to conforming documents and not to the presentation processor), then some explanation of the purpose of constraining the document syntax would be informative.

#color is just one example.
Related Actions Items:
Related emails:
  1. {minutes} TTWG Meeting 21/8/2014 (from nigel.megitt@bbc.co.uk on 2014-08-21)
  2. {agenda} TTWG Meeting 21/8/2014 (from nigel.megitt@bbc.co.uk on 2014-08-20)
  3. {minutes} TTWG Meeting 14/8/2014 (from nigel.megitt@bbc.co.uk on 2014-08-14)
  4. {agenda} TTWG Meeting 14/8/2014 (from nigel.megitt@bbc.co.uk on 2014-08-13)
  5. Re: {agenda} TTWG Meeting 7/8/2014 (from pal@sandflow.com on 2014-08-06)
  6. {agenda} TTWG Meeting 7/8/2014 (from nigel.megitt@bbc.co.uk on 2014-08-06)
  7. {agenda} TTWG Meeting 31/7/2014 (from nigel.megitt@bbc.co.uk on 2014-07-30)
  8. {minutes} TTWG Meeting 24/7/2014 (from nigel.megitt@bbc.co.uk on 2014-07-24)
  9. {agenda} TTWG Meeting 24/7/2014 (from nigel.megitt@bbc.co.uk on 2014-07-23)
  10. {minutes} TTWG Meeting 17/7/2014 (from nigel.megitt@bbc.co.uk on 2014-07-17)
  11. {agenda} TTWG Meeting 17/7/2014 (from nigel.megitt@bbc.co.uk on 2014-07-16)
  12. {agenda} TTWG Meeting 10/7/2014 (from nigel.megitt@bbc.co.uk on 2014-07-09)
  13. {minutes} TTWG Meeting 19/6/2014 (from nigel.megitt@bbc.co.uk on 2014-06-19)
  14. RE: {agenda} TTWG Meeting 19/6/2014 (from mdolan@newtbt.com on 2014-06-18)
  15. {agenda} TTWG Meeting 19/6/2014 (from nigel.megitt@bbc.co.uk on 2014-06-18)
  16. {minutes} TTWG Meeting 12/6/2014 (from nigel.megitt@bbc.co.uk on 2014-06-12)
  17. RE: {agenda} TTWG Meeting 12/6/2014 (from mdolan@newtbt.com on 2014-06-12)
  18. Re: {agenda} TTWG Meeting 12/6/2014 (from pal@sandflow.com on 2014-06-11)
  19. Re: {agenda} TTWG Meeting 12/6/2014 (from nigel.megitt@bbc.co.uk on 2014-06-11)
  20. Re: {agenda} TTWG Meeting 12/6/2014 (from pal@sandflow.com on 2014-06-11)
  21. Re: {agenda} TTWG Meeting 12/6/2014 (from nigel.megitt@bbc.co.uk on 2014-06-11)
  22. {agenda} TTWG Meeting 12/6/2014 (from nigel.megitt@bbc.co.uk on 2014-06-11)
  23. {minutes} TTWG Meeting 5/6/2014 (from nigel.megitt@bbc.co.uk on 2014-06-05)
  24. RE: {agenda} TTWG Meeting 5/6/2014 (from mdolan@newtbt.com on 2014-06-04)
  25. {agenda} TTWG Meeting 5/6/2014 (from nigel.megitt@bbc.co.uk on 2014-06-04)
  26. {agenda} TTWG Meeting 29/5/2014 (from nigel.megitt@bbc.co.uk on 2014-05-28)
  27. Update to ISSUE-305 (from nigel.megitt@bbc.co.uk on 2014-05-23)
  28. {minutes} TTML Meeting of 24/10/13 (from glenn@skynav.com on 2013-10-24)
  29. RE: TTML Agenda for 24/10/13 (from mdolan@newtbt.com on 2013-10-23)
  30. TTML Agenda for 24/10/13 (from nigel.megitt@bbc.co.uk on 2013-10-23)
  31. Re: TML Agenda for 06/08/13 (from glenn@skynav.com on 2013-08-08)
  32. [Minutes] TTWG telecon 08/08/2013 (from tmichel@w3.org on 2013-08-08)
  33. Re: TML Agenda for 06/08/13 (from pal@palemieux.com on 2013-08-08)
  34. TML Agenda for 06/08/13 (from Sean.Hayes@microsoft.com on 2013-08-08)
  35. TTML Agenda for 25/07/13 (from Sean.Hayes@microsoft.com on 2013-07-25)
  36. ISSUE-263: profile feature set may not match intended feature constraints [Simple Delivery Profile for Closed Captions] (from sysbot+tracker@w3.org on 2013-07-17)

Related notes:

[pal]: profile feature set may not match intended feature constraints

24 Oct 2013, 15:31:03

Raised by Mike Dolan
PAL: P1

Philippe Le Hégaret, 24 Oct 2013, 15:32:57

Implemented in https://dvcs.w3.org/hg/ttml/rev/9a3008473dc8.

Glenn Adams, 24 May 2014, 05:05:53

The rationale for why a TTML profile (e.g. SDP-US, IMSC) wishes to constrain the decoder feature set is out of scope of this issue. The presumption is that it is desirable to be able to do so. Every known profile discussed in this WG does so today.

The problem is that there is no way to represent in the profile syntax that a feature is simply constrained without either: 1) adding a new subset #feature to the core TTML spec (e.g. #color-rgb), or 2) omitting the feature (e.g. #color) and defining an extension (e.g. #mycolor).

The problem with #1 is that requires action by W3C - it is arguably a substantive change to the spec and is thus not practical for those defining profiles. But perhaps we could decide that subset features can be administratively added?

The problem with #2 is that it fails to provide any sort of relationship to the TTML feature that is constrains. If a profile signals the extension #mycolor, there is no way to know that the extension is actually a strict subset of #color and thus any decoder that supported #color would also support #mycolor. Maybe we can add an extension parameter that provides such a relationship, e.g. isASubsetOf="#color". But the problem with that is that a decoder may not understand the extension namespace at all. We'd have to require/encourage decoders to parse all extensions with such a parameter.

Mike Dolan, 28 May 2014, 17:11:52

The implementation cited above in https://dvcs.w3.org/hg/ttml/rev/9a3008473dc8 include two new attributes {extends,restricts} which may be used by a profile designer to declare that a {feature,extension} being defined constitutes an extension or restriction, respectively, of another {feature,extension}. Note that a feature definition cannot extend or restrict an extension; however, an extension may extend or restrict a feature.

Glenn Adams, 19 Jun 2014, 13:16:51

As per meeting of 14th August 2014, and Action-323, reassigning this to TTML2. Will open a new issue to update SDP-US to fall in line with TTML2.

Nigel Megitt, 15 Aug 2014, 10:41:28

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David Singer <singer@apple.com>, Nigel Megitt <nigel.megitt@bbc.co.uk>, Chairs, Thierry Michel <tmichel@w3.org>, Philippe Le Hégaret <plh@w3.org>, Atsushi Shimono <atsushi@w3.org>, Staff Contacts
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