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{minutes} TTWG Meeting 2017-03-09

From: Nigel Megitt <nigel.megitt@bbc.co.uk>
Date: Thu, 9 Mar 2017 17:28:35 +0000
To: "public-tt@w3.org" <public-tt@w3.org>
Message-ID: <D4E73D59.3A188%nigel.megitt@bbc.co.uk>
Thanks all for attending today's extended TTWG meeting. Minutes can be found in HTML format at https://www.w3.org/2017/03/09-tt-minutes.html

In text format:


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

                Timed Text Working Group Teleconference

09 Mar 2017

   See also: [2]IRC log

      [2] http://www.w3.org/2017/03/09-tt-irc


          Andreas, Dae, Glenn, Nigel, Pierre, Thierry





     * [3]Topics
         1. [4]This meeting
         2. [5]IMSC
         3. [6]TTML
         4. [7]AOB
     * [8]Summary of Action Items
     * [9]Summary of Resolutions

   <scribe> scribe: nigel

This meeting

   Nigel: We have one main issue to discuss for IMSC, though Mike
   sent his regrets.

   Andreas: I won't be able to join next week.

   Nigel: Okay lets get the views from here then and discuss it
   briefly without fully concluding
   ... until Mike has been able to contribute.
   ... That's all on IMSC. On TTML2 we have a number of issues to
   ... I don't think there are any other main agenda topics, I can
   give an update under AOB
   ... on my trip to CSUN last week.
   ... There's been some progress on moving WebVTT to the next
   working draft but I don't
   ... think that's an agenda item for us today. You'll have seen
   David's encouragement by email
   ... to review and look at the dispositions.
   ... Any other business, or specific points to raise?

   Dae: For IMSC 1.next we are introducing fillLineGap? Will this
   carry forward to TTML2?

   Nigel: Yes we need the semantic in TTML2, and I believe that
   Glenn has begun some work
   ... on it in TTML2.

   Dae: There's no support for it in CSS yet though?

   Nigel: No, I did raise an issue on CSS.

   Pierre: I started a wiki listing CSS features that are needed
   for subtitles. I encourage us to
   ... lobby for this.

   Nigel: +1

   Andreas: A question for Nigel as BBC representative: It's clear
   that BBC guidelines have a
   ... clear requirement documented for this feature. Could this
   be brought to the awareness
   ... of the CSS WG? I think it is nowhere more obvious than in
   the BBC guidelines. It is just
   ... an example but you made a strong point for it too.

   Nigel: Yes absolutely, very happy to do that.



     [10] https://github.com/w3c/imsc/wiki/TTML2-features-for-inclusion-in-IMSC2

   Pierre: That's the list of TTML2 features for inclusion in

   Nigel: There's no pointer to which features are or are not
   doable in CSS?

   Pierre: No, I started doing that with textEmphasis but I
   haven't with anything else.
   ... I can help with the mapping but ultimately Glenn is the
   expert there in terms of TTML2,
   ... so it requires his participation.

   Glenn: If you're talking about CSS mapping I have no interest
   in doing that.

   Dae: I don't mind volunteering to take a first go at this
   because most of the features have
   ... a straightforward mapping or fallback. I wonder how robust
   the fallback has to be?

   Glenn: My solution to mapping to HTML is to map to SVG in HTML.

   Nigel: To an extent that does not fully resolve the problem
   since CSS affects the presentation
   ... of text in SVG in any case and may be used to make it more

   Glenn: I don't recognise that, metadata can be added to SVG to
   make it accessible.

   Nigel: Since IMSC2 is a subset of TTML2 then any features that
   we want to be in IMSC2 need
   ... to be in TTML2. If we need IMSC2 to be mapped to CSS then
   we need to make sure the
   ... fallbacks and limitations are clear.

   Glenn: We decided some time ago to make HTML/CSS mapping
   orthogonal to TTML2
   ... development.

   Dae: I will aim to do a first draft of the CSS mapping before
   next week's meeting.

   Glenn: I don't disagree that it is useful to know where the
   challenges are. If there are tweaks
   ... that can be made to make things a little easier I don't
   generally object to doing that.

   Nigel: We need to pragmatic here - if we are forced to wait for
   a normative reference to
   ... a CSS spec for everything then we will be waiting for a
   long time.

   Dae: I think this is about a fallback in some cases.

   Pierre: For example what is the CSS equivalent of fontShear?

   Glenn: There is none.

   Pierre: We should note it then.

   Glenn: We have not done that in the past. For example in TTML1
   XSL-FO does not support
   ... all the semantics, and there's a note that declares that
   such unmappable semantics exist.
   ... We did not let that gate us for TTML1.

   Pierre: In the scope of IMSC1 features there is in fact a clear
   mapping via XSL-FO to CSS.
   ... XSL says what the differences are between it and CSS.
   That's the case for TTML1 now and
   ... it made the mapping clear and easy to do.

   Glenn: It's under ยง9.3.3 under synchronic flow processing, a
   note about there being no
   ... XSL counterpart.
   ... We've had to go beyond XSL-FO and CSS in TTML2 due to new
   requirements that
   ... still are not satisfied in CSS land.

   Andreas: What we need to acknowledge is that since TTML1
   started as a standard the
   ... importance of CSS mapping has increased in general in the
   domain and for members and
   ... for W3C. For IMSC1 and IMSC2 there may be the situation
   where the industry will not
   ... support a feature without a clear CSS mapping, so I can
   support that for everything we
   ... want to include especially in IMSC we should do everything
   we should do to make it
   ... work with web technology.

   Pierre: Are you opposing doing the mapping work Glenn?

   Glenn: I am not opposing it, I just don't think it is a
   necessary part of TTML2 and can be
   ... done elsewhere.

   Pierre: So you will not object to that or to PRs on TTML2?

   Glenn: Sure, I will consider PRs on TTML2.
   ... The other question that is deeper is that during that
   mapping process there may be a
   ... suggestion to make changes in TTML2, and that's reasonable,
   but we have to ask ourselves
   ... the practical question if waiting for that to be completed
   could become a blocking or gating factor for wide review.
   ... If during the WR process progress is made on this then we
   can look at that and decide
   ... if we want to make any changes as we come to CR to
   accommodate that.

   Nigel: [draws this discussion to a close]



     [11] https://github.com/w3c/imsc/issues/213

   Nigel: I am not sure what the outstanding points are with this
   that need to be discussed.

   Andreas: I think the last edit from Pierre would be fine. Nigel
   you brought in an extra
   ... issue which is how far you give a recommendation or
   requirement for how far foreign
   ... namespace content should be defined. My view is this is not
   in scope of IMSC or TTML
   ... so would not be necessary, but it is just a recommendation
   so I wouldn't object to it.

   Nigel: It's even weaker than that - it's an informative note
   only to say that it is a good idea
   ... to define a content specification but I agree that we
   cannot force people to make good
   ... implementations!
   ... It's in a pull request:


     [12] https://github.com/w3c/imsc/issues/217

   Pierre: Now Mike has told me he wants to be specific about
   exactly which elements
   ... support foreign namespace elements and which do not, but I
   do not want to rewrite
   ... TTML1!

   Nigel: There are 3 new things since last time:
   ... 1. If we should remove the exception for the tt element?
   ... 2. Clarify that foreign namespace attributes are permitted
   on all TTML1 elements.
   ... 3. Add an informative note about good practice for content

   Pierre: I think there's a dispute that has not been resolved
   where Mike wants to introduce
   ... consideration of XML Schema validation.

   Nigel: I think that's further than we should go.

   Andreas: First I thought we do not need to be as specific as in
   TTML1 but now when I look
   ... at it maybe it would be good to document it wherever it is,
   because for example
   ... <style> does not allow <tt:metadata> as a child element,
   which differs from what the
   ... EBU group does, and has done for years, so there are people
   making mistakes on this.

   Pierre: So you're supporting Mike's idea of explicitly listing
   the elements where metadata
   ... is permitted?

   Andreas: I can understand not wanting to put too much in the
   IMSC spec but somewhere
   ... it should be documented.

   Pierre: My reluctance is simply that it requires interpretation
   of TTML1, which I typically
   ... recommend we don't do, but if we feel it is useful and Mike
   thinks so then maybe it
   ... is enough.

   Nigel: I really like the way it is done now by referring to
   Table 3 in TTML1.

   Pierre: It is wrong though because for example <head> permits
   metadata. Maybe we should
   ... for simplicity just list the elements directly.

   Nigel: OK, I'm fine with listing in an informative note the
   elements. That's probably a service
   ... to the world.

   Pierre: In that case I'm happy to do it.

   Nigel: The second point is to be clear that foreign namespace
   attributes are permitted on
   ... all TTML1 elements.
   ... I think if we are going to summarise what TTML1 permits we
   should do it accurately.
   ... I went to the trouble of checking TTML1 and in fact every
   element defined in that spec
   ... permits foreign namespace attributes.

   Pierre: The risk is that people should go and read TTML1.

   Glenn: I agree that we should not paraphrase TTML1, it's okay
   to have a generic note saying
   ... to see TTML1.

   Nigel: Summarising, there's a concern that we should not list
   things that are defined in TTML1.
   ... For me, I think we should either summarise correctly or not
   at all.

   Pierre: I think you and Mike are agreed on that.
   ... I will list all the elements that permit foreign namespace
   metadata and change the lsit
   ... of elements in TTML1 that permit foreign namespace

   Nigel: Moving on to the note about content specifications, the
   note I have added is:
   ... "For validation purposes it is good practice to define and
   use a content specification for all foreign namespace elements
   and attributes used within a Document Instance. "
   ... The reason I think we should do this is from going back to
   the text in TTML1 about
   ... validation, you may end up with non-pruned foreign
   namespace elements that should
   ... be validated against a content specification, and this
   provides a small hint to plug that gap.

   Andreas: I will not object, but I would prefer not to do this.
   It could be good practice also
   ... to ignore unexpected content.

   Pierre: I will add that paragraph, update the PR. If Mike is
   happy then we go ahead. If not then maybe the solution is to
   remove that paragraph.
   ... if that also satisfies Mike.

   Nigel: Ok I wouldn't object to that if it gets us to consensus.
   ... OK that's all for IMSC, let's take 2 minutes and come back
   for the next hour on TTML.


   Dae: I'd like to clarify if we are addressing horizontal review
   comments before CR?

   Glenn: When I made that comment I did not plan to have to
   resolve all HR comments prior
   ... to going to WR. I did not mean I would not address them if
   possible. I think it is still an
   ... open issue about if we need to resolve them prior to going
   to WR.

   Nigel: We will need to make a call when we want to resolve to
   publish the WR for WD.

   Pierre: I recommend assigning issues.

   Glenn: I don't object to assigning issues to get more people
   working on them however I
   ... will need to do the merge so that will depend on the effort
   I have to do the editorial tasks.
   ... I have no objection to others preparing PRs. I might
   delegate the merge task to others if
   ... time is limited. I need to have oversight on the final

   Nigel: I don't think we should have a blanket policy on pushing
   all HR issues out to after WR.
   ... We need to be able to take it on a case by case basis.

   Pierre: For issue 233 on HDR that's a blocking issue for
   ... I'm happy to prepare a PR for it.

   Glenn: Sure.


     [13] https://github.com/w3c/ttml2/issues/233

   Pierre: I will prepare a PR for that.

   Nigel: I expect a BBC proposal also, for the non-absolute
   luminance case.
   ... I've assigned that issue to you and me, Pierre.

   Dae: If anyone else feels there is a specific issue that we
   must resolve as soon as possible
   ... then it would be good to make that known.

   Pierre: Assigning issues is an approach that works well, where
   the assignee needs to propose
   ... a disposition.

   Nigel: By the way I have one, the audio description one:


     [14] https://github.com/w3c/ttml2/issues/195

   Pierre: We need to document any deferred issues and agree them
   in the group based on the rationale.

   Nigel: On the AD issue I have done the pre-editing work to
   define the semantics and Glenn
   ... is in progress on the editing.

   Pierre: For the TTML1 issues that flow into TTML2 also then in
   my view they all must be
   ... resolved. They're bugs.

   Glenn: I have probably different criteria for bugs.

   Pierre: There are a bunch of "discussed and agreed" issues.

   Glenn: They're well up on my priority list and I'm trying to
   get through them whether they
   ... are labelled as bugs or not.
   ... I'm working on the 58 issues marked TTML2WR but I have no
   objection to anyone
   ... else assigning themselves to an issue.

   Pierre: An efficient solution is not to ignore issues and
   respond to them sooner otherwise
   ... things will get worse in the future and people might get

   Glenn: I'm not trying to make any decisions for the group by
   the way, I'm just labelling
   ... what I am working on.

   Pierre: I have to leave now.

   Nigel: By the way Andreas left before the TTML agenda item too.

   Dae: I would like to raise the bopomofo issue


     [15] https://github.com/w3c/ttml2/issues/253

   Glenn: This refers to a particular script which is used in
   Taiwan to annotate Chinese
   ... in pedagogical works. I would not expect it to be seen in
   subtitling except possibly in
   ... educational programmes for children. It is only really used
   when teaching children in
   ... Taiwan how to read Chinese.

   Nigel: I think we should put this on hold until Richard's
   request to @bobbytung gets a
   ... response, and act on that response when it comes. It may be
   that we decide this is not
   ... high enough on our priority list and we choose to go ahead
   without Bopomofo support.
   ... I did want also to discuss the em units issue:


     [16] https://github.com/w3c/ttml2/issues/216

   Glenn: On that particular issue there is an editorial point on
   the text which I would like to
   ... be opened as a new issue.
   ... That one wasn't an early merge.

   Nigel: That's strange, I commented that it was an early merge
   and marked as one, but the
   ... history doesn't show that. I'm a bit confused about that.
   ... It turns out that Pierre and I had similar editorial
   comments, so I guess we can raise those
   ... as new issues.
   ... There may be some consensus on the 3D and images issue:


     [17] https://github.com/w3c/ttml2/issues/239

   Nigel: The last points by Mike, Pierre and I are that we do not
   need to have left/right images.

   Glenn: On the point about using condition I would like to add
   named parameters there.

   Nigel: I don't think that's necessary but I would not object to

   Glenn: I can do that very quickly and post a PR that does that
   and see what comments there are.

   Nigel: The only reason against doing that is if it generates
   additional test cases that we do
   ... not actually need. Otherwise I don't have a problem with

   Glenn: I'll add a comment to the effect that this is what I
   will do.

   nigel: The next issue I listed was the TTML1 pull request:


     [18] https://github.com/w3c/ttml1/pull/233

   Nigel: This is one of Andreas's.

   Glenn: We had the whole issue of whether padding should be on
   the inside or the outside of regions.
   ... I see this is a note. I need to do more than just add this,
   I would need to add an errata
   ... info and change info, but I see you made a suggestion.
   ... So, mutatis mutandis, we can mark this as discussed and

   Nigel: I think so.

   Glenn: That means "the necessary changes having been made"

   Nigel: I've logged that on the issue.
   ... What about the open pull request?


     [19] https://github.com/w3c/ttml2/pull/273

   Dae: Richard raised issues 274 and 275 based on that.

   Nigel: Oh right I did not realise the relationship was there,
   there's no tracing in the issues or the pull request.

   Dae: I think there's another one aside from 274, it might not
   be 275.


   Nigel: Last week I went to the CSUN annual conference on
   assistive technology and presented
   ... on AD in TTML2 (current status anyway, and desired end
   goal) and also on live subtitles
   ... in TTML via the EBU-TT Live work.
   ... There was a really good and engaged audience for the AD in
   TTML2 talk, and in fact
   ... there were a number of AD talks over the conference. There
   turns out to be a use case
   ... for pan, and also for SSML for text to speech, for example
   to disambiguate different ways
   ... of processing a number like 1876 that could be a year or a

   Glenn: I do not want to embed the whole of another language
   into TTML2!
   ... Also it would be difficult where they have created new
   elements and put attributes on those.
   ... What I have done is to create new attributes only to keep
   it consistent with how TTML does things.
   ... We have very strongly avoided elaborating our element

   Nigel: Understood. Anyhow I thought it is worth mentioning this
   may be a good time to take advantage of the groundswell of good
   ... Thanks everyone. [adjourns meeting]

Summary of Action Items

Summary of Resolutions

   [End of minutes]

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