ISSUE-263: profile feature set may not match intended feature constraints [Simple Delivery Profile for Closed Captions]

ISSUE-263: profile feature set may not match intended feature constraints [Simple Delivery Profile for Closed Captions]

http://www.w3.org/AudioVideo/TT/tracker/issues/263

Raised by: Mike Dolan
On product: Simple Delivery Profile for Closed Captions

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.

Received on Wednesday, 17 July 2013 19:14:57 UTC