{Minutes} TTWG Agenda 2019-08-29

Thanks all for attending today’s TTWG meeting. Minutes can be found in HTML format at https://www.w3.org/2019/08/29-tt-minutes.html.

In text format:


   [1]W3C

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

                Timed Text Working Group Teleconference

29 Aug 2019

   [2]Agenda

      [2] https://github.com/w3c/ttwg/issues/57

   See also: [3]IRC log

      [3] https://www.w3.org/2019/08/29-tt-irc

Attendees

   Present
          Cyril, Nigel, Gary, Glenn, Andreas, Pierre, atsushi

   Regrets

   Chair
          Nigel

   Scribe
          Cyril, nigel

Contents

     * [4]Topics
         1. [5]this meeting
         2. [6]support for font in IMSC
         3. [7]TTML2 issues
         4. [8]Add #direction-version-2 feature designator.
            w3c/ttml2#1024
         5. [9]Constrain maximum value of @length on data element.
            ttml2#1023
         6. [10]TPAC
         7. [11]360 subtitles
         8. [12]TTML2 issue 950
         9. [13]Constrain ttp:profile's @use attribute (#1029).
            ttml2#1137
        10. [14]Fonts
        11. [15]meeting close
     * [16]Summary of Action Items
     * [17]Summary of Resolutions
     __________________________________________________________

this meeting

   <atsushi> (will join after i18n WG call ends, sorry)

   <cyril> scribe: Cyril

   nigel: today I did not put any Webvtt topic
   ... do you need anything?

   gkatsev: no

   nigel: I pulled out 1 dusty IMSC issue
   ... I don't know if we can get anything on the charter
   ... TPAC planning, we should spend at least 10min at the end
   because it's coming up quickly
   ... is there any AOB?

   atai2: I would like to give an update on the 360 activity

   glenn: I added an agenda label on some TTML2 issues
   ... issue 950 and PR 1137

support for font in IMSC

   <nigel> github: [18]https://github.com/w3c/imsc/pull/485

     [18] https://github.com/w3c/imsc/pull/485

   nigel: this PR was opened 22 days ago
   ... there was some comment on it
   ... there was a comment about choosing the compatibility with
   font
   ... the reference to 14496-22

   pal: the reason I referenced 14496-22
   ... is because in an IMF forum this the reference that has been
   suggested
   ... this is a reference to Open Type
   ... that's the first that came to mind
   ... because that's what's used in existing applications of IMSC
   ... when downloadable fonts are used

   glenn: I don't like refering to a content type format
   specification directly
   ... we should be referring to MIME media type values
   ... and refer to the definitions, like font/off
   ... I would like to see it changed
   ... rather than referring to the ISO specification

   pal: I'm comfortable with that
   ... I want to use font/otf

   glenn: fine for me

   nigel: Open Type fonts can be wrapped into WOFF
   ... is it the intention that WOFF or WOFF2 are not permitted?

   pal: on practical experience, font/otf will work
   ... people have been using it
   ... so mandating support for it is not an issue
   ... there are some politics/drama about WOFF
   ... I don't know what it means exactly

   <nigel> [19]CSS font-face src descriptor

     [19] https://drafts.csswg.org/css-fonts-3/#src-desc

   pal: but I'm uncomfortable with adding WOFF

   glenn: WOFF can take multiple types of fonts than OTF
   ... you would have to restrict WOFF
   ... I think I agree with Pierre on this

   nigel: the font-face src property lists many types of possible
   font faces
   ... CSS would allow other options that are being prevented here
   ... including SVG fonts
   ... which is interesting for the use case that we are trying to
   support (icons)

   cyril: I'm not sure there is widespread support for SVG fonts

   glenn: agree with Cyril
   ... unless there is a strong support for a given font format it
   is fine to limit it to OTF for now
   ... we can add more later

   pal: until there is concrete explanation of why WOFF is
   necessary, I suggest sticking with OTF for now

   nigel: so the proposal is to adopt initially only OTF
   ... do we have consensus?

   cyril: I agree

   nigel: no objection

   RESOLUTION: IMSC font support will initially only support OTF

   cyril: I would like to make sure that we have the right
   restrictions on the different elements and attributes

   nigel: there are similar comments in the issue
   ... about how the font element sources are defined and there
   seems to be a bit of ambiguity
   ... is it ok to have no sources for the font element or more
   than one
   ... my reading was that you needed 1 and may have more than one
   ... glenn suggested to have an src attribute

   pal: the reason I went the children way was to enable
   alternatives
   ... it wasn't clear to me that you could use multiple font
   elements

   glenn: you cannot have multiple font elements with the same
   family name

   pal: that's my guess but it was not clear in the spec

   glenn: the font family attribute can be a list of font family

   cyril: exactly

   pal: you could have different font elements, each with an src
   attribute, and call them font1, font2, font3 and use these
   values in the fontstyle attribute
   ... I did consider that but thought it wasn't clear
   ... that's why I ended up where we are

   nigel: I agree that the most elegant way to have alternative is
   to use multiple source elements
   ... but having zero elements does not make sense

   pal: I agree
   ... my proposal is to say that TTML2 requires one source
   element to be present if the src attribute is not specified

   <inserted> nigel: that works for me, thank you, and a note in
   the IMSC spec pointing out that at least one is required would
   help.

   cyril: what is the use case for specifying alternatives?

   pal: if one source is broken, you have a choice for another one
   ... or a backup online vs embedded in the multiplex

   glenn: also switching between different types

   cyril: I would hate to have 2 ways to do the same thing

   nigel: it's not clear that the fall back algorithms are the
   same for alternate sources vs alternate fontFamily

   glenn: using the range attribute you may have multiple fonts

   cyril: I'd like to keep it simple for the simple use case

   pal: the basic use case is a font element 2 children, one for
   the multiplex and one for the online version, no glyph subset,
   etc.

   cyril: not even sure that this is the basic use case for
   Netflix, it could be even simpler
   ... I'm not saying the Netflix use case should be the only use
   case

   glenn: we don't have enough information about the use cases but
   we need an initial proposal

   nigel: the main question is do we allow a single source (with
   src attribute) or multiple sources (children and no src)
   ... at the moment we don't support multiple formats
   ... but supporting multiple source elements seems future
   looking

   pal: I did not want to have support for src attribute and
   source elements

   cyril: what about data?

   pal: the term external resource excludes using data

   glenn: external means not in the document

   pal: right, so no data

   cyril: I'm confused with "Partially supported via
   <code>#embedded-data</code>"

   nigel: I made a similar comment in the thread
   ... and made some suggestion

TTML2 issues

Add #direction-version-2 feature designator. w3c/ttml2#1024

   <nigel> github: [20]https://github.com/w3c/ttml2/issues/1024

     [20] https://github.com/w3c/ttml2/issues/1024

   nigel: this PR covers special inheritance semantics
   ... adding direction to p is not a change as this was in TTML1
   ... Pierre do you think the new feature designator is not
   needed

   pal: I don't think we need a new designator, because it was
   clear in XSL before
   ... to the extent that you have to look at XSL, and it is
   unambiguous

   cyril: are you saying this behavior applies to TTML1 already?

   pal: I think so and I think IMSC.js supports that

   <nigel> [21]XSL definition

     [21] https://www.w3.org/TR/2006/REC-xsl11-20061205/#direction

   nigel: I can see your point Pierre
   ... you might argue that TTML2 might benefit from a note about
   that
   ... the XSL specification says it is a modification compared to
   the CSS specification

   glenn: in TTML1, it says that it is based on XSL 1.1

   pal: IMSC.js code mentions XSL
   ... so this was already specified in TTML1

   <nigel> [22]CSS 3 Writing Modes section on Principal Writing
   Mode.

     [22] https://www.w3.org/TR/css-writing-modes-3/#principal-flow

   glenn: so it would be useful to add a note, saying it's not new
   and closing this issue

   <nigel> +1

   nigel: I agree

Constrain maximum value of @length on data element. ttml2#1023

   <nigel> github: [23]https://github.com/w3c/ttml2/issues/1023

     [23] https://github.com/w3c/ttml2/issues/1023

   glenn: the only place where it might be useful to have a
   constraint is when you have base64 data
   ... you could have an infinitely long document
   ... so I was proposing to limit that to 4GB

   cyril: Isn't this an application-level constraint

   nigel: yes

   glenn: application can do that so probably no need to put a
   constraint in the spec
   ... there is a difference in code
   ... if you are writing a validator, you cannot use a 32 bit
   integer for the size

   nigel: I propose to close the issue with no change
   ... any objection

   RESOLUTION: we close issue 1023 with no change

TPAC

   nigel: there is a proposed time at 9:30 am to have a joint
   meeting with CSS
   ... I've requested a meeting with the Chinese IG
   ... but had no response yet

   <atsushi> +1

   nigel: if you have an issue with that 9:30 time, send me a
   message otherwise I'll reply that we agree
   ... the wiki page has had some updates with topics
   ... we need to look at the schedule
   ... the week before TPAC I'll be travelling
   ... so next week is the last time when we could discuss this

   cyril: should we have a 2h meeting next week

   nigel: yes

   pal: I'll be available only for 2nd hour

   nigel: anything else on TPAC?

   pal: I've changed my schedule and will be attending the IG from
   Monday

360 subtitles

   atai2: I've drafted an explainer for this activity with
   requirements
   ... sent it to the incubator
   ... will be discussed on monday at TPAC

   nigel: if this is not on the wiki page of TPAC, please add it

TTML2 issue 950

   glenn: my only point is that I added one more comment

   <nigel> github: [24]https://github.com/w3c/ttml2/issues/950

     [24] https://github.com/w3c/ttml2/issues/950

   glenn: we cannot remove the set element, my explanation is
   there
   ... I verified that the algorithm needs it

Constrain ttp:profile's @use attribute (#1029). ttml2#1137

   <nigel> github: [25]https://github.com/w3c/ttml2/pull/1137

     [25] https://github.com/w3c/ttml2/pull/1137

   glenn: the PR has been opened for 27 days, I need a review

Fonts

   pal: I ran into a problem in practice and wanted to know if
   people had it
   ... in Digital Cinema subs, you can do manual kerning at the
   markup level, specifying positive/negative spacing

   glenn: letter spacing can be used for that, including negative

   pal: is there a reason to do that in the markup vs in the font?
   ... I've seen fonts with no embedded kerning at all

   glenn: many CJK fonts have fixed width for all glyphs and no
   kerning
   ... it's not unusual
   ... if it's an open type font you can use a gpos table
   ... to fine tune the position based on context
   ... it can be done in the fonts
   ... TTPE supports gpos and gsub

   pal: that's my understanding
   ... is there any reason why someone would not want to do it at
   the font level?

   glenn: lack of access to changing the font, IPR reasons for
   example

   pal: the font that I saw was a subset so the font had been
   modified, so the IPR argument does not hold

   nigel: glenn said you can put a single character in a span and
   apply letter spacing, where would the spacing apply: before or
   after?

   glenn: you'd have to put it around a pair of characters
   ... with some limitation that you cannot overlap the markup

meeting close

   <nigel> scribe: nigel

   Nigel: Thanks everyone, we're over time, so I'll adjourn now.
   Thank you Cyril for scribing. 2 hour meeting next week so we'll
   begin an hour earlier. [adjourns meeting]

Summary of Action Items

Summary of Resolutions

    1. [26]IMSC font support will initially only support OTF
    2. [27]we close issue 1023 with no change

   [End of minutes]
     __________________________________________________________


    Minutes manually created (not a transcript), formatted by
    David Booth's [28]scribe.perl version 1.154 ([29]CVS log)
    $Date: 2019/08/29 16:32:40 $

     [28] http://dev.w3.org/cvsweb/~checkout~/2002/scribe/scribedoc.htm
     [29] http://dev.w3.org/cvsweb/2002/scribe/

Received on Thursday, 29 August 2019 16:36:26 UTC