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{minutes} TTWG Meeting 2017-03-30

From: Nigel Megitt <nigel.megitt@bbc.co.uk>
Date: Thu, 30 Mar 2017 15:50:00 +0000
To: Timed Text Working Group <public-tt@w3.org>
Message-ID: <D502E7A8.3BCCD%nigel.megitt@bbc.co.uk>
Thanks all for attending today's TTWG meeting. Minutes can be found in HTML format at https://www.w3.org/2017/03/30-tt-minutes.html

In text format:


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

                Timed Text Working Group Teleconference

30 Mar 2017

   See also: [2]IRC log

      [2] http://www.w3.org/2017/03/30-tt-irc


          Nigel, Glenn, Thierry, Andreas

          Pierre, Dae




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

   <scribe> scribe: nigel

This Meeting

   Nigel: For today we have some updates on IMSC and some TTML
   issues. Any other business?

   group: [no other business]

   Nigel: Next week I will not be available, and nobody has
   offered to Chair. Any volunteers?

   Andreas: I may also not be able to attend next week.

   Nigel: If anyone does want to Chair next week's meeting please
   let me know by Tuesday
   ... at the latest and I will be able to assist with any queries
   ... Otherwise the default position may be that we do not hold a


   Nigel: My update is that after publishing the WD for Wide
   Review Thierry sent the horizontal
   ... review and internal dependency review messages out to other
   W3 groups.

   Thierry: I have sent the questionnaire to the group and that is
   holding back the request to
   ... TAG. That's the only one that is pending.

   Nigel: Thank you. And I sent all the external liaisons. It
   turns out that DLNA is no longer
   ... operating, so I could not send to them. I got several
   responses back from people saying
   ... they had received it and would provide feedback.
   ... Thierry sent that questionnaire out on 24th March. Any
   queries on that now?

   Thierry: I reused the wording from TTML. Probably what may be
   missing is stuff about the
   ... use of images in IMSC1.

   Nigel: I see that the answer to 3.6 needs editing to remove
   audio and condition for example.

   Thierry: Ok

   Nigel: If you make those edits then we can approve the updated
   text by email. I think the
   ... remaining responses are uncontroversial.

   Thierry: I will do that right now.

   Nigel: We had one issue raised on IMSC this week that is of
   some interest:


      [9] https://github.com/w3c/imsc/issues/224

   Nigel: This is about whitespace handling.

   Glenn: The issue here is that the wording of XSL-FO makes it
   hard for me to determine if
   ... the intent is to fully translate all whitespace that is XML
   whitespace into 0x20 space characters.

   Nigel: I had the same issue, I wasn't sure exactly what it was
   trying to say or if there is some
   ... order of precedence in applying the various rules.

   Glenn: The problematic part is whether or not collapse
   semantics apply, and it seems like
   ... you can read it that for the first character in a sequence
   of whitespace, if it is not a space,
   ... then you might not collapse it. I do not think that is the
   intent and I do not know of any
   ... implementation that does not translate tab in that context
   into space, so I think implementations
   ... should collapse it.

   Nigel: I think my colleague Chris (who raised the issue) has an
   implementation that seems
   ... to have this behaviour of retaining the first tab, and
   seems to obey the letter of the
   ... specification rather than the intent.

   Glenn: I think the Antenna House and FOP implementations do it
   differently, so the question
   ... is I guess what we really want to happen. If we want that
   tab to be normalised to space
   ... then we need to fix up our spec. My suggestion is to add
   language to TTML1 and TTML2
   ... to have that effect. Even if we do not translate it into
   space there is certainly no suggestion
   ... that it be translated into an alignment or some spaces.

   Nigel: Even if no alignment and no spaces a tab would be
   expected to have some inline width.

   Glenn: Usually a tab character is not in a font and is mapped
   to zero width. It has no
   ... inherent width semantics.
   ... Probably any fonts that do have a tab character map it to
   zero width or to the space glyph.

   Andreas: I have a question regarding Chris's original question.
   He asked on the basis of
   ... Example 7 of IMSC 1.0.1?

   Nigel: Yes.

   Andreas: So actually we did not provide the source for the

   Nigel: Yes, we do.
   ... The way the spec is structured the example is an XML
   document that is imported by the
   ... HTML and then formatted. So the tabs are really there.

   Glenn: We should fix the example.


     [10] https://www.w3.org/TR/ttml-imsc1.0.1/#itts-fillLineGap

   Nigel: Yes I agree and Pierre has indicated he agrees with
   that, on the issue.

   Glenn: I agree with Andreas however, that said, I think we
   should remove the tabs.
   ... There's another property called whitespace-treatment ...

   Nigel: There are 4 properties defined by TTML1:


     [11] https://www.w3.org/TR/ttml1/#content-attribute-space

   Glenn: If you look at 7.16.8 in XSL 1.1 on whitespace

   <glenn> [12]https://www.w3.org/TR/xsl/#white-space-treatment

     [12] https://www.w3.org/TR/xsl/#white-space-treatment

   Nigel: Since we use suppress-at-line-break=auto that means only
   U+0020 is suppressed,
   ... and everything else is retained.

   Glenn: Correct.
   ... Under 1.2.1 under paging and scrolling it talks about
   splitting things like whitespace
   ... into separate properties for greater control. The intent
   was to derive those properties
   ... from CSS2, in this case the CSS2 property called
   "whitespace". So to follow the implementation
   ... path of other implementations we probably want to go and
   look at CSS2 whitespace.

   <glenn> [13]https://www.w3.org/TR/REC-CSS2/cover.html#minitoc

     [13] https://www.w3.org/TR/REC-CSS2/cover.html#minitoc

   Glenn: The initial value of whitespace is "normal" which
   directs user agents to
   ... "collapse sequences of whitespace, and break lines as
   necessary to fill line boxes"
   ... and does not make a distinction between different kinds of

   Nigel: If you follow the link it defines whitespace as:

   -> "Only the characters "space" (Unicode code 32), "tab" (9),
   "line feed" (10), "carriage return" (13), and "form feed" (12)
   can occur in whitespace. "

   Glenn: Exactly. These are the same as XML whitespace. It looks
   like there's a bug in XSL-FO here.
   ... I wonder if this was updated in a later version of XSL-FO.
   ... Perhaps Steve Zilles would be a good person to ask about

   Andreas: I think we could also contact Tony Graham who is at
   Antenna House.

   Glenn: We should certainly contact Steve as he is still active
   in W3C whereas Tony is not.

   Nigel: Which should we do first, contact Steve or create the
   issues on TTML?

   Glenn: I will create the issues and link them to the IMSC issue
   from Chris and articulate
   ... the problem as I see it and then we can use that as
   reference material in an email to
   ... Steve and Tony.
   ... I know both Steve and Tony so I can ask them. Since I chair
   the Apache group on FOP
   ... I have a link there too.

   Nigel: Okay, that's a plan, thank you.
   ... I will add a note to the issue.


     [14] https://github.com/w3c/imsc/issues/224#issuecomment-290434056



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

   Nigel: This raised some eyebrows, since there was already a
   pull request that Pierre had
   ... opened on request.

   Glenn: I always edit pull requests before applying them to add
   my imprimatur and make
   ... sure they are consistent.

   <tm> using PR is not 10 yeras of process ...

   Nigel: From a process point of view, we had
   [16]https://github.com/w3c/ttml2/pull/283 which
   ... the Group requested from Pierre to resolve the issue he
   raised, which was closed without
   ... any communication and it was not obvious why. The branch
   for the pull request could
   ... easily have been modified in place rather than closing and
   opening a new one, which
   ... would have been less work and would have made the
   provenance clearer.

     [16] https://github.com/w3c/ttml2/pull/283

   Glenn: One thing here was that the branch was not properly
   named and had things in
   ... which were not done in the right way. There was no
   intention to raise tensions.

   Andreas: This is an interesting discussion - things like GitHub
   have changed the way that
   ... groups can collaborate on specification texts. I think we
   appreciate that the Editor here
   ... has a different view maybe. We as a Group should decide on
   what the process is that
   ... we use, and also recall that proposals and changes can be
   made onto the pull requests.

   Nigel: By the way you can rename a branch if that is the issue.

   Glenn: It is not so straightforward because the pull request
   doesn't get modified. It is okay
   ... to do it locally before pushing to the remote, but when
   pushing to the remote things
   ... get locked in.
   ... The only substantive point on this particular issue is the
   name. I've stated my opinion
   ... on that. I don't think adding length to the name has any
   improvement. That's my opinion.

   Nigel: The name needs to reflect the scope of application,
   which is much narrower than it
   ... is specified at the moment, and appears to apply to all HDR
   content rather than
   ... just those HDR schemes that require it.
   ... This also needs to be reflected in the specification text,
   which likewise needs
   ... to be narrowed to schemes such as PQ HDR.

   Glenn: Looking at the original proposal, that referred to
   images, which I took out.
   ... I took "image" to refer to the content on which it is
   composited rather than a referenced
   ... PNG or JPEG image in an <image> element. Is that not right?

   Nigel: No that's correct I think it is about the video images,
   for example.

   Glenn: Pierre used the term "target image" and I changed it to
   "target medium" - I found
   ... ways to eliminate the use of "image".
   ... The other thing is that the example has the unexplained
   value 2.4 so I added "where the
   ... exponent of 2.4 is the gamma correction applied by the
   EOTF". I may have been wrong
   ... in that but that was my interpretation.
   ... Just below the syntax box there is an equation that uses
   the term "normalized" which
   ... I assume meant application of the gamma of 2.4.

   Nigel: That's the root of the problem - there is another scheme
   for HDR that does not use
   ... the luminance gain approach at all but uses a different
   approach varying the gamma.

   <glenn> [17]https://en.wikipedia.org/wiki/Gamma_correction

     [17] https://en.wikipedia.org/wiki/Gamma_correction

   Andreas: I have to drop off now. Thank you.

   Nigel: By specifying tts:luminance and using this kind of
   wording it looks as though we are
   ... promoting one particular scheme for HDR, which is not what
   we should be doing at all.

   Glenn: I was not aware of that context.

   <tm> OK bye

   Thierry: [drops off call]

   Glenn: I did not make any other changes here.
   ... Actually I did fix another change which was an error - he
   had an integer type but in the
   ... examples used non-integer numbers so I changed to a
   non-negative real number.
   ... I also added continuous animation support. Any numerical
   value I make continuous.

   Nigel: By the way the other colour space that is often used is
   BT.2020 - we currently only
   ... refer to BT2100 in Appendix P. So there needs to be some
   work here to make this
   ... more neutral.

   Glenn: Please note that people file new issues on the text
   rather than piling comments on
   ... to the original issue. We can always point back to the
   original issue.

   Nigel: Can I just check - are there other branches with work in
   progress on them that
   ... are not yet complete and might be worth review?

   Glenn: I have about 10, particularly Audio Description. I'm
   hoping we do not slide too far
   ... beyond the end of the month. The other one that is higher
   up on my list is the one that
   ... came up last week regarding Andreas's pull request on

   Nigel: I see that just Glenn and I remain on the call so we
   should probably close!

   Glenn: I will take a look at Andreas's pull request and may
   need to make some changes to it.

   Nigel: If you can edit the branch that is the source of the
   pull request that will be better.
   ... Even if you commit directly to that branch.

   Glenn: Okay I will give that a go.

   Nigel: Ok thanks, see you in a couple of weeks. [adjourns

Summary of Action Items

Summary of Resolutions

   [End of minutes]

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