{Minutes} TTWG Teleconference 2025-08-28

Thanks all for attending today’s TTWG meeting. Minutes can be found in HTML format at https://www.w3.org/2025/08/28-tt-minutes.html


In plain text:

   [1]W3C

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


                Timed Text Working Group Teleconference

28 August 2025

   [2]Previous meeting. [3]Agenda. [4]IRC log.

      [2] https://www.w3.org/2025/07/31-tt-minutes.html

      [3] https://github.com/w3c/ttwg/issues/314

      [4] https://www.w3.org/2025/08/28-tt-irc


Attendees

   Present
          Andreas, Cyril, Dana, Gary, Nigel, Pierre

   Regrets
          Chris_Needham

   Chair
          Gary, Nigel

   Scribe
          nigel

Contents

    1. [5]This meeting
    2. [6]IMSC 1.3
    3. [7]DAPT
    4. [8]WebVTT open issues
         1. [9]Interop meetings
         2. [10]Can ::cue(selector) match a list of webvtt node
            objects? w3c/webvtt#533
         3. [11]WebVTT should allow pages to modify the caption
            display area w3c/webvtt#531
    5. [12]TPAC 2025 planning
    6. [13]Meeting close

Meeting minutes

  This meeting

   Nigel: Today: DAPT, IMSC 1.3, WebVTT, TPAC 2025 planning
   … Anything else, or points to make sure we cover?

   nothing extra

  IMSC 1.3

   Nigel: We're waiting for Wide Review here.

   Pierre: We're only waiting for HR from Accessibility
   … The TAG delegated it to internationalisation, who are
   satisfied, so they're both closed.
   … Privacy and Security, I think were not unhappy, but have not
   closed their issue.
   … The ones we've not heard from are folks in the accessibility
   group.

   Gary: Looks like no response on the privacy ticket, only on the
   security request.

   Pierre: We had requested for a response before Sep 16 so you or
   I could ping the privacy folk
   … and also remind the accessibility folks.

   Nigel: It was assigned 2 weeks ago so someone is looking at it.

   Nigel: Feels like a "friendly reminder" message.

   Pierre: Yes, we should do that on both privacy and
   accessibility

   Nigel: I feel like I should do it.

   Pierre: Thanks.

   Gary: I don't know if you want to close the security request
   ticket since it sounds resolved.

   Nigel: I've added a message to that ticket asking if okay to
   close.
   … I've also added friendly reminders to the other two open
   tickets

   Nigel: Anything else for IMSC?

   Pierre: Nothing that I know of.

  DAPT

   Nigel: Seems like current status is that Atsushi raised HR
   issues for the CR snapshot and we're
   … waiting for responses.
   … They're logged under [14]w3c/dapt#307
   … Seems like he did that last week
   … I think we're just waiting now.
   … Anything else on DAPT?

     [14] https://github.com/w3c/dapt/issues/307


   Cyril: No, no updates on DAPT

  WebVTT open issues

    Interop meetings

   Gary: I wanted to mention the Interop meetings

   Dana: If it would be helpful I can send another email.
   … We've had 2 meetings so far.
   … Every other Wednesday.
   … Next is Sep 10
   … Goal is to clean up the test suite enough that we can
   eventually be an Interop focus area
   … We've been going through the tests all the browsers are
   failing
   … and identifying test issues.
   … Found a few, and raised some issues.
   … The first is one that's been open a while, which is 531.

   Nigel: A reminder of that interop work might be helpful

   <gkatsev> [15]interop webvtt repo

     [15] https://github.com/web-platform-tests/interop-webvtt/


   Dana: WebVTT was accepted as an Interop investigation area
   which means that work is needed
   … to fix up the test suite before it can be a focus area.
   … We're going through the tests one by one and checking if it
   is valid, up to date, and bug free
   … We're looking for as many people who are interested to join.
   … Next meeting is Sep 10.

   Gary: I posted the repo

   [16]Details for the next meeting

     [16] https://github.com/web-platform-tests/interop-webvtt/issues/11


   Dana: Even if someone doesn't have time to go through tests,
   they're still welcome to
   … go to the meetings and join in on discussions about what to
   do about faulty tests

   Nigel: Any questions?

   Pierre: I maintain ttconv which is a timed text conversion
   library.
   … Folk have bugged me and provided pull requests to add support
   for vertical text in WebVTT,
   … and that had not been done originally because the support
   levels in players didn't allow for testing.
   … Last time someone suggested this and added a pull request
   they mentioned that their
   … reference player is video.js.
   … Is that a good reference? I'm trying to avoid merging
   something that turns out not to be valid
   … or contains the wrong WebVTT.

   Gary: video.js uses the most maintained version of vtt.js and I
   believe (not checked recently)
   … that it has the correct vertical positioning.

   Pierre: Is video.js going to be included in the interop
   testing?

   Gary: The main focus is the native browser user agents

   Pierre: I'm trying to resist the temptation to add something
   that works great in video.js
   … only to find out that no browser implements it and then we've
   done worse.

   Gary: That's a downside of the web platform tests vs the
   implementation report.
   … The WPT is more aimed at browsers, whereas the implementation
   report is about "any" implementations at all.
   … The first step is what Dana mentioned, figuring out if the
   tests are correct.

   Pierre: Theoretically you could use ttconv to convert TTML
   tests to WebVTT tests but then
   … you're introducing another variable.
   … There's obviously a need for this but I've been reluctant to
   committing something that's bad.

   Gary: I'm pretty sure Safari does vertical text correctly,
   because I fixed it.

   Pierre: Maybe you could add to that issue?

   [17]sandflow/ttconv#449

     [17] https://github.com/sandflow/ttconv/issues/449


   Pierre: Thanks for the wisdom!

    Can ::cue(selector) match a list of webvtt node objects?
    [18]w3c/webvtt#533

     [18] https://github.com/w3c/webvtt/issues/533


   github: [19]w3c/webvtt#533

     [19] https://github.com/w3c/webvtt/issues/533


   Dana: This is about ::cue pseudo element.
   … You can add a selector to that as an argument.
   … We're finding that all of the browsers are failing the tests
   where the selector is * or :root
   … When we consult the WebVTT specification we find that it's
   ambiguous.
   … It's not spelled out if those selectors are supposed to be
   supported.
   … One idea that I think I agree is to have the only allowed
   type selectors be the explicit VTT classes
   … like bold, underline, voice, language, ruby text, so we have
   a concrete list of type selectors,
   … and the universal or root selector wouldn't be supported.

   Gary: The issue is that the spec implies that bare text nodes
   should be selected, but it's not clear.
   … Should the * match those as well as the explicit tags.
   … No browser implements selection of the explicit tags without
   the text nodes ("internal node objects")
   … But whether it should is unclear.

   Nigel: What are the use cases?

   Dana: It's for styling the internal nodes within the cues, e.g.
   make all bold elements green.
   … The use case for the * selector is covered by the pseudo
   element without the selector argument,
   … because that already matches to the cues.

   Andreas: Thanks for bringing this up.
   … For confirmation, if you have cue text and you want to apply
   CSS styles to all of them,
   … then you can already do that by using ::cue without a
   selector?

   nods

   Andreas: And the * selector most likely is supposed to do the
   same thing?
   … But it's ambiguous if it includes text enclosed by tags.
   … It's questionable why you should exclude it.
   … Why should the * selector give the same results as no
   selector?

   Gary: Given that it's covered, unclear in the spec and not
   implemented, we can remove it
   … from the spec and call it a day.

   Dana: Would the spec change be to say that the 8 or so type
   selectors are the only allowed ones?

   Gary: I think that might be the best course of action, to be as
   explicit as possible.

   Nigel: Are you saying that * selector applies to tagged text
   only, or to remove *?

   Gary: The first, that it applies to tagged text only.

   Nigel: What's the relationship between that and Dana's
   suggestion of limiting the set of tags?
   … Sounds like an orthogonal issue.

   Gary: The spec lists the node objects, which are the untagged
   text objects.
   … Simon suggested the root element never match. I guess that
   would be an alternative,
   … to say that internal node objects don't match the * selector.

   Andreas: I'm also a bit confused. I thought that your approach
   would be to remove the * completely,
   … but you're now saying to keep it but make the semantics only
   apply to text inside tags?

   Gary: Yes, I don't know if we can remove it completely.

   Andreas: If it's ambiguous and not properly implemented then
   this way is also not properly implemented, right?
   … Why are you using this kind of solution?

   Nigel: you mean what is the * for at all?

   Andreas: Yes, if it's ambiguous and not properly implemented,
   why target a specific different meaning?
   … What points you to this solution?
   … If it's used already and people have a different
   interpretation, then some existing WebVTT
   … files might then have a different presentation, and users
   would not be happy.

   Dana: That's a good point. I'm not sure which solution I like
   best.
   … I'm thinking, in terms of ease of implementation, there could
   be a potential problem to have
   … the * only apply to internal text and not the root, because
   then we have other selectors
   … like the id selector that would need to match the root.

   Gary: One of the ambiguities is that it says, maybe we used the
   terms incorrectly,
   … that it matches any internal node object and that includes
   both tags with existing names
   … and those without explicit names, like times.
   … and then it says leaf nodes are not matched, and those
   include text or fragments of text.
   … There's that ambiguity that fragments seem to be listed as
   matchable but then later on it says
   … leaf node objects cannot be matched.

   Dana: Are you talking about how the spec says in one place that
   leaf node objects are separate
   … from internal node objects and then later on it says they are
   a subset of internal node objects?

   Gary: Yeah, I guess this isn't straightforward.
   … I think the main question is that in the cue selector it has
   a table of things it should be able
   … to match and the question is what it means by "other
   elements".
   … I think we need to review the spec again because it's very
   likely that we still need a clarification
   … but maybe the spec is clearer than on first reading, and the
   tests may not be correct.

   Andreas: As a suggestion, you might want to consult the meeting
   archives to find a better hint
   … on the intent.

   Nigel: Good point, why is it written the way it is written?

   Dana: I'm curious if we say that a selector matches a leaf node
   object, like a text node object,
   … is that referring to the text content within a span, which
   you cannot style?
   … When they said you cannot target the leaf node objects maybe
   that's what they're talking about.

   Gary: It could be the same as HTML where you cannot target text
   but you can target the span that they're in.

   Dana: If you can't target that then you target the root.

   Gary: Yes, that would be the ::cue

   Dana: Another way is to say it matches both the root and any
   internal nodes.

   Nigel: Another way is to say the * matches on the tag name, and
   not on null, so the root would be excluded.

   Gary: That's what it seems like it wants to do.
   … Then :root would not be allowed as a selector, and * would
   not match against :root

   Nigel: Why not allow :root?
   … From an implementation perspective would you not have the
   default selector for ::cue be ::cue(:root)?

   Gary: The options are either * and :root are allowed or
   explicitly not allowed.
   … Since it's also a CSS extension and the implementations are
   lacking we can decide to simplify it.

   Nigel: What's the next step?

   Gary: Immediate next step is to read through the spec again to
   exactly understand what it means
   … by internal node objects and leaf node objects and see if
   there's any history about the intent.

   SUMMARY: @danae404 and @gkatsev to re-read the spec about
   nodes, and check the archives for history about the intent.

   Dana: Are there publicly available notes about the development
   of WebVTT spec?

   Gary: I think they are, and there's discussion on GitHub.

   Andreas: Some of it will be in the text track community group.
   There may have been
   … some in the WHATWG too so you may have to look at different
   sources.

   Gary: Some of the old FOMS websites when WebVTT was first
   developed have some notes too.

    WebVTT should allow pages to modify the caption display area
    [20]w3c/webvtt#531

     [20] https://github.com/w3c/webvtt/issues/531


   Dana: There's no good way to test that WebVTT cues move out of
   the way when controls are showing
   … because every browser has different default controls. The
   spec doesn't state anything about
   … where the cue should be so it's up to the implementation to
   check where the cue moves to
   … when controls show.
   … We deleted 3 tests that had arbitrary positioning that didn't
   correspond with any real implementation.
   … We're hoping to accurately test that cues move out of the way
   of controls.
   … One way is to expose a pseudo-element for the controls bar so
   we can query its location
   … and make sure it doesn't overlap with the cue.

  TPAC 2025 planning

   Nigel: The schedule has been published.
   … Typically we create a wiki page for TPAC, for the group.
   … I may have taken an action to do that last time.
   … The key thing we need is a list of agenda topics.
   … It's also useful to know who will be attending.

   Andreas: I will be attending, and was thinking about discussing
   DVB work that has happened lately.
   … 2 years ago we discussed a proposal for signalling subtitles.
   … There's now an ETSI publication on that.
   … That could be addressed, and some other new developments in
   DVB.
   … We can check with Chris Needham - it may fit in the joint
   meeting with the MEIG,
   … but the signalling of the purpose of subtitling could good to
   discuss at TPAC.

   Nigel: Thank you.
   … TPAC must be 9-10 weeks away so now is the time to focus on
   this.

   Gary: I won't be there in person but the beginning of the
   sessions are in my evening and not too
   … late so I plan to join remotely.

   Nigel: That might affect the ordering of our topics.
   … We typically list in person attendees, I will send a link
   when I have made it.

   Dana: I will be remote too.

   Gary: The timezone should be better for you on West Coast than
   me.

   Dana: I would like to continue discussing WebVTT interop.

  Meeting close

   Nigel: Thanks all, we're out of time for today. Next meeting is
   in 2 weeks, on 2025-09-11.
   … [adjourns meeting]


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