{Minutes} TTWG Teleconference 2022-10-27

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   [1]W3C

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


                Timed Text Working Group Teleconference

27 October 2022

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

      [2] https://www.w3.org/2022/10/13-tt-minutes.html

      [3] https://github.com/w3c/ttwg/issues/230

      [4] https://www.w3.org/2022/10/27-tt-irc


Attendees

   Present
          Andreas, Atsushi, Nigel, Pierre

   Regrets
          Cyril, Gary

   Chair
          Nigel

   Scribe
          nigel

Contents

    1. [5]This meeting
    2. [6]Coalesce empty ISDs into non-empty ISDs w3c/imsc-hrm#50
    3. [7]Rechartering Formal Objection Council status update
    4. [8]Meeting close

Meeting minutes

  This meeting

   Nigel: Without Cyril, not sure we should look at the DAPT
   issues.

   Nigel: So that leaves IMSC-HRM and any news on the Charter FO.
   … Any other business?

   Andreas: Nothing from me

  Coalesce empty ISDs into non-empty ISDs w3c/imsc-hrm#50

   <Github> [9]https://github.com/w3c/imsc-hrm/pull/50 : Coalesce
   empty ISDs into non-empty ISDs

      [9] https://github.com/w3c/imsc-hrm/pull/50


   github: [10]https://github.com/w3c/imsc-hrm/pull/50


     [10] https://github.com/w3c/imsc-hrm/pull/50


   Nigel: Pierre and I had a design chat about this last week

   Pierre: Yes, I'd like to share my latest thoughts. I've spent a
   lot of time on this.
   … [shares screen]
   … [screen shows updated model with a switch between the
   presentation buffer and the display, to allow
   … clearing to happen by not compositing]
   … The path I'm going down as a proposal is that every ISD that
   comes in, decide if it is empty or not.
   … If it is not empty, go through the same process as the
   current HRM.
   … If it is an empty ISD, toggle the output of the current
   model, to turn off the output of the presentation buffer.
   … The idea is that an empty ISD is empty so there is nothing to
   display.
   … What it really means is that the cost of processing empty
   ISDs is zero because there is nothing to render.
   … Separately Nigel and I discussed whether or not there should
   be additional constraints on the
   … duration of empty ISDs, to catch errors seen in IMSC files
   where very small gaps are introduced
   … erroneously.
   … Nigel also mentioned that setting minimum time constraints on
   an ISD might reflect refresh rates etc.
   … I'm not so concerned about this because there's already text
   about the refresh rate possibly not being
   … as fast as needed to show every ISD.
   … Those are my thoughts.

   Nigel: Thanks for that. How would it work here if there were a
   25th of a second gap between two
   … non-empty ISDs?

   Pierre: The switch would open, so nothing would be available
   for display, at the end of the non-empty ISD.
   … While the previous non-empty ISD is being displayed, the next
   non-empty ISD is being drawn into
   … the alternate presentation buffer. When the very short empty
   ISD occurs, the switch opens,
   … independently of the presentation buffer.
   … When the empty ISD ends it closes and the next non-empty ISD,
   drawn into the alternate presentation buffer,
   … is moved into the active presentation buffer and is
   displayed.

   Andreas: When a non-empty ISD follows another non-empty ISD the
   presentation buffer will stay as it was
   … before, but it will be toggled so nothing is sent to the
   display?
   …

   Pierre: Exactly.

   Andreas: When a non-empty ISD comes up is there an additional
   action to clear the display?

   Pierre: The assumption is that it costs nothing to display
   nothing.
   … In a traditional graphics system with a graphics plane with a
   front and back buffer, the assumption is
   … that disabling compositing with the graphics plane is a zero
   cost operation.

   Andreas: OK

   Pierre: In modern systems that is true.

   Andreas: Maybe there is no cost associated with it, but you may
   have to delete a DOM node or whatever, in HTML,
   … so there is something that needs to be done.

   Pierre: If you're using cues, when no cue is displayed there is
   no work.
   … There's work in preparing a non-empty cue but there's no such
   thing as an empty cue, just no cue.

   Andreas: That's right, but there is no duration with the ISD
   that you send to the display, right?

   Pierre: The way the HRM is written, the output of the
   presentation buffer is "made available" to the display.
   … That's really broad, "display", here. It depends on how fast
   the output rendering device can go.
   … The HRM says today that it is conceivable that a non-empty
   ISD, that has content, is so short, that it will
   … never be displayed because it comes between two refresh
   cycles of the display. That's already acknowledged
   … by the HRM.

   Nigel: If I understand right, this model will not catch very
   short empty ISDs?

   Pierre: I've agonised over this.
   … I really like the idea of catching errors, making an
   integrated SHALL statement in the model.
   … But even with non-empty ISDs we can't guarantee they will be
   displayed.
   … I've been agonising about a SHALL or a SHOULD for the minimum
   duration of a sequence of empty ISDs.
   … The other question is what should the lower bound of that
   duration be?
   … Another important point for the notes:
   … Going back to the minimum duration of empty ISDs, I'm
   uncomfortable:
   … Netflix has a min duration of 2 frames, I've heard 3, maybe
   1, but nobody ever says what the frame rate is!
   … So I'm not sure what the right lower bound is.
   … Having a SHOULD for any validator to warn if there is an
   empty ISD shorter than 1/30s, but making
   … it a normative SHALL requirement is another thing.

   Nigel: That's a strong argument: if we don't have data points
   to support SHALL statements we ought not to have them.

   Pierre: A SHOULD would not be bad to have, but it would be a
   heuristic. I'd say right now, that neither
   … 608 or STL can have gaps shorter than 1/30s but it is
   possible with EBU-TT-D say.

   Nigel: [asks about the edge case of a very short non-empty ISD
   and empty ISD followed by a non-empty ISD]

   Pierre: The cost of clear is still present for erasing the
   presentation buffer, that doesn't change.

   Nigel: Yes, I see.

   Pierre: The minimum duration of a non-empty ISD has not
   changed.

   Nigel: No, it has, because it now also includes the duration of
   a following empty ISD whereas before it did not.

   Pierre: Right, absolutely, you could have a non-empty ISD
   that's a millionth of a second followed by a
   … relatively long empty ISD - before, that was not possible.

   Nigel: Worth noting, it may already be present, that this is
   not about the readability complexity,
   … but the presentation complexity.

   Pierre: I'm going to note that, maybe make sure there's a
   statement like that in the document.
   … I'll update the pull request.

   Nigel: Thank you!

   Pierre: Thank you for hearing me out.

   SUMMARY: @palemieux to update the pull request

  Rechartering Formal Objection Council status update

   Atsushi: No update, it's possible that in near future I will
   hear back.

   Pierre: Thank you for that.

   Atsushi: The latest document for FO is at the same URL as the
   previous one so you can see the FO Council report.

   [11]Team Report on Timed-Text WG Charter Formal Objection

     [11] https://www.w3.org/2022/09/ttwg-charter-fo-report.html


   Nigel: Thanks, that incorporates the Chairs response from me
   and Gary.

  Meeting close

   Nigel: Thanks everyone, that's completed those parts of the
   agenda that we could do today.
   … Let's adjourn a little early. [adjourns meeting]


    Minutes manually created (not a transcript), formatted by
    [12]scribe.perl version 192 (Tue Jun 28 16:55:30 2022 UTC).

     [12] https://w3c.github.io/scribe2/scribedoc.html





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Received on Thursday, 27 October 2022 15:57:42 UTC