{minutes} TTWG Meeting 2014-12-18

Thanks all for attending today's TTWG meeting, and for your work over the past year.

Minutes for today's meeting, in HTML format are at http://www.w3.org/2014/12/18-tt-minutes.html

In text format:


      [1] http://www.w3.org/

                Timed Text Working Group Teleconference

18 Dec 2014

   See also: [2]IRC log

      [2] http://www.w3.org/2014/12/18-tt-irc


          nigel, glenn, tmichel, Mike, pal, Andreas





     * [3]Topics
         1. [4]This meeting
         2. [5]Action Items
         3. [6]Issues
     * [7]Summary of Action Items

   <trackbot> Date: 18 December 2014

   <scribe> scribeNick: nigel

This meeting

   nigel: introduces agenda
   ... Is there any other business?

   pal: I'd like to review the TTML2 timeline and the IMSC 1
   timeline if there's time at the end, and perhaps
   ... start to think about IMSC 2 timeline.
   ... and how long it takes to complete PR review, i.e. PR -> Rec
   ... This is because there are other organisations that are
   considering using those specs.

Action Items


   <trackbot> action-359 -- Thierry Michel to Draft a message re
   imsc 1 cr test suite and implementation and a list of bodies to
   send it to. -- due 2014-12-18 -- OPEN


      [8] http://www.w3.org/AudioVideo/TT/tracker/actions/359

   tmichel: I sent the message, and copied to the member-tt list
   and I sent it to all the people that are listed
   ... on our charter as liaison and the others to whom Nigel sent
   the wide review messages, and two
   ... coordination groups.
   ... I copied pal, plh, nigel and dsinger.

   close action-359

   <trackbot> Closed action-359.


   <trackbot> action-360 -- Nigel Megitt to Send liaison request
   on behalf of w3c ttwg to arib -- due 2014-12-18 -- OPEN


      [9] http://www.w3.org/AudioVideo/TT/tracker/actions/360

   nigel: I have begun drafting this and have addresses for the
   recipients - they have requested a paper
   ... document requesting the liaison. I have more to do on this.



   <trackbot> issue-21 -- window anchor points not supported? --
   pending review


     [10] http://www.w3.org/AudioVideo/TT/tracker/issues/21

   glenn: I haven't received any comments on any of the issues
   that I've marked as Pending Review
   ... I guess most likely people haven't had a chance to dive
   into it. I suggest we close this and if an issue
   ... arises then it can be filed.

   close issue-21

   <trackbot> Closed issue-21.


   <trackbot> issue-236 -- Character spacing, i.e. letter-spacing
   -- pending review


     [11] http://www.w3.org/AudioVideo/TT/tracker/issues/236

   glenn: this is based on the CSS attribute of the same name, so
   should be quite straightforward.
   ... This was to define a property to control tracking and to
   allow the tracking value to be
   ... specified, a typographic term that refers to the spacing
   between characters. There's a
   ... related issue called kerning. It turns out that one of the
   Japanese deployed specifications has
   ... an attribute to turn on and off kerning. Japanese doesn't
   usually use kerning, but it may be
   ... useful for embedded latin scripts. To support that we need
   to have a property font-kerning
   ... as specified in the CSS3 font module - I'll add an issue
   for that.

   <scribe> ACTION: glenn Raise an issue for font-kerning in TTML2
   [recorded in

   <trackbot> Created ACTION-362 - Raise an issue for font-kerning
   in ttml2 [on Glenn Adams - due 2014-12-25].

   close issue-236

   <trackbot> Closed issue-236.


   <trackbot> issue-237 -- Inline space -- pending review


     [13] http://www.w3.org/AudioVideo/TT/tracker/issues/237

   glenn: This allows the author to define a space in the inline
   progression direction.

   close issue-237

   <trackbot> Closed issue-237.

   nigel: Last week we could not close a number of issues related
   to the ttm:item solution.
   ... There has been some discussion - I'd like us to get to
   sufficient consensus for FPWD, even if
   ... later we modify it based on further discussion, e.g. prior
   to CR.

   glenn: There were 2 issues raised - one related to validation
   of the content of the item element,
   ... noting that we don't have a constraint that all spec items
   can be validated by XML Schema.
   ... Though I guess that a constraint based on the content type
   of ttm:item based on the name
   ... and a lookup may be validatable using Schema 1.1.

   nigel: Really?

   glenn: It would have to have name -> type dereferencing logic.
   I haven't tried it.
   ... The other issue is regarding the value definition of names.
   Nigel proposed that we should
   ... find a way to [scribe misses audio]. The most appropriate
   mechanism I think is to use
   ... the xml namespace mechanism, to allow a prefix to qualify
   the name, where the prefix
   ... can be resolved to a URI that doesn't have to be reused
   every time (i.e. it's inherited). So I
   ... propose to change the syntax of name to NCName or an
   unqualified name - if an unqualified
   ... name then it would be implied to be within the TTML
   namespace definition, e.g. the "TT
   ... metadata items namespace". For people who want to define an
   alternate namespace for a
   ... defining authority or classification scheme, then e.g.
   "ebuttm:" could be used and then
   ... somewhere in the document associate that namespace with the
   prefix. Then the name value
   ... in ttm:item would be name="ebuttm:whatever". That's my
   suggested way to handle name
   ... extension mechanisms and to have a shorthand for the prefix

   Andreas: In general I think that's a reasonable concept
   proposal, and will be worth reviewing.
   ... For me, this is a complete concept to integrate metadata in
   TTML without dependent on the
   ... TTML publication process. I can see the reasoning to find a
   way to handle metadata independently
   ... of the rest of the specification. I don't want to block the
   FPWD process though I think it
   ... does need more review. I think this should be put into the
   WD and should be reviewed by
   ... e.g. EBU to see how it matches with the current mechanism.
   Regarding validation, it would
   ... be good to have a position about it, how important current
   validation mechanisms are for
   ... standardisations of new items. From a practical view some
   validation mechanisms are more
   ... used than others. I'd welcome other views on this as well
   as mine - are there other users
   ... whose workflow depends on validation?

   glenn: Thinking of the practical consequences of e.g. using XSD
   formally, and then we say that
   ... we're going to interpret every TTML constraint that can be
   expressed in XSD then that would
   ... be quite a task even for TTML1. For example the rules on
   the timing expression and a variety
   ... of other expressions are just xs:string because writing out
   a regular expression or schema
   ... syntax for some of the more complicated attributes may be
   extremely difficult - e.g.
   ... length and time expressions. Regardless of RNC or XSD we
   didn't go as far as possible. We
   ... ended up incorporating some of those - e.g. textDecoration
   has all possible combinations
   ... enumerated in the schema, but in other cases it's
   difficult. The practical consequences of
   ... pushing XML schema more. And we didn't have TTV for example
   available at that time. There's
   ... a place for validators and verifiers that can go further
   than schema validators.

   pal: For metadata that is purely descriptive, why even create
   an equivalent in TTML2 and not
   ... just encourage metadata to be added in foreign namespaces?

   glenn: We don't say anything about that - we imply that it's a
   reasonable approach. The reason
   ... I chose to try to pull in the existing metadata that I
   could find between SMPTE-TT and EBU-TT
   ... was because I think a lot of it has general utility to TTML
   and having it defined in one place
   ... is a good thing to do. If we had gone down that path in
   TTML1, when we reviewed some
   ... specific metadata items from Dublin Core and MPEG-7 we
   decided we weren't ready to
   ... define them. Since then we've deployed, different groups
   have proposed specific metadata
   ... items and I think now's the time to bring them into TTML
   unless there's a good reason not to.
   ... That allows them to be commonly used.

   pal: I appreciate the goal. I see a danger: e.g.
   CEA608CaptionService. The definition of that item
   ... is substantively different than RP2052-10 that's supposed
   to be equivalent. How can we
   ... avoid confusion between those two parameters that look like
   they're supposed to be the same?

   atai: I see the same danger for EBU-TT vocabulary.

   glenn: I want to know what the difference is because I tried to
   stay faithful to the existing
   ... definitions where I put the prefix cea on them - I added
   that prefix because I recognised
   ... that the way it was defined in the RP you referred to was
   quite specific to CEA608 and I
   ... didn't think it was appropriate to make it more generic. I
   haven't yet refined the value type
   ... definition to be more refined than e.g. xs:string. You can
   view all of the xs:string ones as a
   ... "tbd" to plug in the more specific definition.

   pal: Okay, I still see the danger of having two metadata
   definitions that could both be present
   ... and have different values.

   glenn: I'm expecting a translation process. It's possible just
   to reference RP2052 directly,
   ... but then we'd define very few values or have to normatively
   reference downstream specs,
   ... which I've commented on before. We could argue that RP2052
   is not downstream from TTML2
   ... but from TTML1 so technically that might not be a circular
   reference, but if it ever changed
   ... to refer to TTML2 then I'd still have that concern.

   pal: We could resolve that by communicating with SMPTE who
   could act on that. There's
   ... another possibility, which is simply to do nothing, and
   leave those metadata items in SMPTE
   ... and non-normatively point the reader at them.

   glenn: Yes, that's an option, or we could define something that
   points at the SMPTE document
   ... to get the value definition.
   ... (with a normative reference)
   ... Other than the circular reference problem I don't see any
   problem with that.
   ... I also see a value in enumerating the values here, as a
   single point of reference.

   atai: I agree with pal's argument - I would favour a solution
   where the TTWG, SMPTE and EBU
   ... find a way to coordinate their metadata efforts to create
   an interoperable solution without
   ... conflicting definitions or the possibility of confusing
   ... On validation mechanisms, not everything can be validated
   in Schema 1.0 but specific
   ... constraints like the existing of metadata elements could be
   validated with Schema 1.0 and
   ... that would not be the case with the proposed solution.

   mike: It's important that even if there's a general way of
   adding metadata we are clear how to
   ... replicate what's in 2052-10. There may be a transitory
   period where there could be some
   ... confusion, until the responding organisations update their
   specifications to reference the TTML2 work as needed..

   glenn: There's a different point about bringing things into
   TTML and then revising external
   ... specs. The reason I brought these into TTML2 was because
   nigel, mike, andreas and pal had
   ... followed a bunch of issues saying we should support these
   metadata. Now it sounds like you're
   ... saying you don't want a new mechanism.

   mike: For SMPTE and DECE the intent was to sweep the metadata
   into TTML2 and then reference
   ... it, removing the metadata from the SMPTE and DECE. That's
   the long term plan. The requests
   ... from SMPTE and DECE to add these items was for that
   purpose. Provided the semantics are
   ... the same or at least subsettable then that follows the

   atai: I'm not sure about the EBU requests for adding metadata
   vocabulary - I think we have to
   ... go back and look at that. I thought the request was to add
   the metadata in the ebu namespace.
   ... EBU needs to consider this further. Also there have been
   some comments from John Birch
   ... on the list. For me, I would abstain and we can proceed
   with this and then review by other groups.

   glenn: It seems as though all the issues can be surmounted by
   adding more spec text.
   ... If there are semantic discrepancies then they can be fixed.
   I'm not hearing any strong objection
   ... to moving forward with that in the FPWD. I propose closing
   these issues en masse and then
   ... reviewing post FPWD.

   nigel: I was going to make that proposal myself.

   pal: I have a problem - the FPWD doesn't need to be perfect,
   but the definitions should at least
   ... be a superset of the SMPTE ones - that needs to be fixed
   before the FPWD. That doesn't
   ... sound like a lot of work.

   glenn: Please tell me what's broken specifically.

   pal: RP2052-10 section 5.6 has a specific definition of a
   caption service - that doesn't exist
   ... in TTML2.

   glenn: There's an Editorial note to further specify the details
   of the named items.

   nigel: There's clearly some editorial work to be done as
   described by Glenn earlier, as well
   ... as the editorial points on each metadata items.

   glenn: This is a blocker as raised by pal. If we insist on this
   then it will push the dates back
   ... by a month or so. I wanted to get all the main Change
   Proposals marked as implemented.
   ... That doesn't prevent us from dealing with all the issues.

   nigel: I was referring to the technical changes - I think that
   the editorial notes are okay for a FPWD
   ... as long as it's clear where work is needed.

   glenn: I agree with that - or we could remove all the items,
   but I think that would be a disservice.

   nigel: Given the state of this discussion and the outstanding
   technical edits I can't close these
   ... issues at this time, so I'll have to hold them open until
   the new year.
   ... Apologies for not getting to the other business. Wishing
   everyone a good couple of week's
   ... break if you're getting one, and see you in January. Thanks
   for all your work this year.

   glenn: Mele Kalikimaka! - Merry Christmas in Hawaiian!

   nigel: yes, Happy Christmas too. [adjourns the meeting]
   ... Oh, forgot to add, since we closed Issues 236 and 237 we
   can close CP20.

Summary of Action Items

   [NEW] ACTION: glenn Raise an issue for font-kerning in TTML2
   [recorded in

   [End of minutes]

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Received on Thursday, 18 December 2014 16:16:51 UTC