{Minutes} TTWG Face to face meeting 2024-09-27

Thanks all for attending today’s TTWG face to face meeting at TPAC. Minutes can be found in HTML format at https://www.w3.org/2024/09/27-tt-minutes.html


We made 3 resolutions:

  *   Resolution 1<https://www.w3.org/2024/09/27-tt-minutes.html#r01>: Proceed with a minor revision of IMSC as detailed in the minutes
  *   Resolution 2<https://www.w3.org/2024/09/27-tt-minutes.html#r02>: Liaise with ARIB about feature improvements in IMSC, specifically the backlog issues
  *   Resolution 3:<https://www.w3.org/2024/09/27-tt-minutes.html#r03> Merge the open Pull Requests and then go through the admin needed to get a WG decision to request transition to CR

The third resolution concerns DAPT specifically.

Those minutes in plain text:

   [1]W3C

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


                Timed Text Working Group Teleconference

27 September 2024

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

      [2] https://www.w3.org/2024/09/12-tt-minutes.html

      [3] https://github.com/w3c/ttwg/issues/291

      [4] https://www.w3.org/2024/09/27-tt-irc


Attendees

   Present
          Atsushi, Bernd, Chris_Needham, Cyril, Dana,
          Eric_Carlson, Gary, James_Craig, Jean-Yves_Avenard,
          Jer_Noble, Nigel, Pierre, sideshowbarker,
          Surya_Sunkavelli

   Regrets
          -

   Chair
          Gary, Nigel

   Scribe
          nigel, cyril, atsushi, gkatsev, cpn

Contents

    1. [5]Introductions
    2. [6]Agenda bash
    3. [7]Netflix demo of TTAL <--> DAPT
    4. [8]Streamable Text Tracks
    5. [9]IMSC
    6. [10]Next part of the day's meetings
    7. [11]Afternoon session
         1. [12]IMSC (continued)
         2. [13]WebVTT Interop and issues
         3. [14]New ATTRIBUTES block w3c/webvtt#523
         4. [15]DAPT
         5. [16]Break
    8. [17]TTML2
         1. [18]TTML2 CR snapshot outdated banner
         2. [19]TTML Media Type Definition and Profile
         3. [20]Joint meeting follow-ups
    9. [21]Conclusion
   10. [22]Summary of resolutions

Meeting minutes

  Introductions

   Nigel: Nigel Megitt, BBC, co-chair TTWG

   atsushi: Atsushi Shimono, W3C Japan, team contact TTWG

   jcraig: James Craig, Apple, accessibility groups like ARIA,
   crossing over to groups like this when there's an overlap of
   interest

   cyril: Cyril Concolato, Netflix

   gkatsev: Gary, Invited Expert, NBC Universal/Peacock, co-chair
   TTWG and WebVTT editor

   pal: Pierre-Anthony Lemieux, supported by MovieLabs, editor
   IMSC

   surya: Surya Sunkavelli, working on ...

   Surya: Hey everyone, my name is Surya Sunkavelli. I work on the
   Media Foundations team within Encoding at Netflix so my work
   usually features studio facing use cases and media inspection
   related projects. With that being said, lately I’ve been
   working with Cyril for about a couple months now in tracking
   the DAPT spec as it develops and gets

   updated and mapping it back to TTAL, which is a Netflix
   internal script file exchange format used to interchange
   between third party dubbing tools and Netflix internal tools
   like Scripting tool.

  Agenda bash

   nigel: Iterates through topics

   [23]Meeting topics

     [23] https://www.w3.org/wiki/TimedText/tpac2024#Topics


   <jernoble> +present Jer Noble

   group discussion of agenda topics and timings

   [24]Results of agenda bash

     [24] https://github.com/w3c/ttwg/issues/291#issuecomment-2379654028


  Netflix demo of TTAL <--> DAPT

   surya: TTAL is an internal Netflix specification for script
   file exchange
   … I wanted to demo the status of the converter between TTAL and
   DAPT
   … and the key DAPT features that are being mapped properly

   cyril: Netflix blog post explaining TTAL

   jcraig: This is not a programming script, but a script for a
   piece of media?

   cyril: Yes, think of it like a transcript

   [25]https://netflixtechblog.com/

   introducing-netflix-timed-text-authoring-lineage-6fb57b72ad41

     [25] https://netflixtechblog.com/introducing-netflix-timed-text-authoring-lineage-6fb57b72ad41


   cyril: this explains the history behind TTAL
   … It is already used in production, we have partners all around
   the world
   … that deliver scripts, dubbing scripts mostly but also audio
   description scripts
   … using this format, but Netflix wants to migrate to DAPT when
   it is finalised.

   surya: [shares screen]
   … List of example DAPT files generated by the converter.
   … [shows example file]
   … xml:lang showing language of file
   … daptm:langSrc to show origin language
   … daptm:represents - I know this is going to change, but looks
   like this now

   cyril: Mentioned previously - Netflix commissioned production
   of dubbing scripts for some
   … of its open content, where we share content that can be used
   to test features like HDR etc.
   … One of the titles we have is Meridian and we have asked for
   the generation of dubbing scripts
   … in ~8 languages. We intend to release that as open source too
   so
   … people will be able to see the TTAL and DAPT scripts for this
   title.

   surya: Yes, I can see around 8 languages.
   … Here's an example of one of the Meridian ones.
   … This one is an audio description script.
   … It's mapped to visualNonText and visualText
   … With frame rates, we capture that using ttp:frameRate and
   ttp:frameRateMultiplier.

   Nigel: are you using frame based time expressions?

   surya: In TTAL we use frame based time expressions, so we do
   the same in DAPT

   cyril: This is the easiest conversion. We may decide to have a
   different mode where
   … we go to seconds and forget the frame rate.

   surya: Features prefixed with nttm: is for Netflix internal
   metadata from TTAL.
   … We're just storing them here but we're still talking about
   how best to organise internal specific metadata.

   cyril: There are so many ways to capture metadata, attributes,
   elements, metadata elements,
   … either one or multiple.
   … Would like to have guidance in DAPT about how people should
   do metadata.

   surya: Events and Characters

   cyril: In this example here, there is a `ttm:desc` child of a
   `ttm:agent`
   … Not sure if that's allowed?

   nigel: ttm:agent does not accept ttm:desc children

   surya: That's something to keep in mind for agents, where to
   store the metadata

   nigel: One option is to change it in TTML2

   surya: Specific elements, div captures ids, begin and end
   times, style ids
   … so the mapping from the events to the style ids.
   … ttm:agent reference, which we map back to ttm:agent elements
   … One issue we haven't finalised yet, is that TTAL and DAPT
   think differently about how to
   … map script events or timing events. We haven't ironed out the
   mapping yet, some issues with TTML.
   … We would like segments to map to span elements with time
   offsets and styles for dubbing.
   … Have to finalise that still.
   … Earlier mentioned daptm:represents, so with the introduction
   of that we will change
   … how we use daptm:eventType

   Nigel: Reminding myself, we got rid of event type didn't we

   cyril: Yes, it's now represents

   cyril: To summarise, no problem mapping the core types of TTAL
   into DAPT
   … The question is about mapping additional metadata that is not
   in the core DAPT vocabulary
   … How best to use the registries or user defined values for
   some of the attributes
   … That's what we have to work on now

   Nigel: Will you share those more widely to see if there's
   interest in adding those to the registries?

   Cyril: Yes, some of them

   Nigel: That's great, a working implementation of a DAPT
   generating tool

   <eric_carlson> +present eric_carlson

   surya: Yes, and there's a tool to go back the other way that
   we'll complete

   cyril: This tool will be open sourced

   nigel: Thank you for that demo

  Streamable Text Tracks

   Nigel: In Media WG yesterday I raised a follow-up to a
   conversation in Media and Entertainment
   … Interest Group from Monday,
   … which was about adding to the Media Source Extensions text
   tracks; it's currently only audio and video.
   … There was a positive discussion, with consideration of some
   of the thorny technical issues
   … that would need to be resolved.

   Cyril: Would like to go through the issues and understand which
   groups will deal with them.

   jer: Two major areas are streaming of raw formats, WebVTT in
   hls.js, and feature level compat
   … between MSE and HLS, and how to append WebVTT files
   … The MSE API allows you to append in a blob of binary data
   with a specific MIME type
   … The concept would be you could init a source buffer with a
   MIME type of webvtt and append chunks
   … of WebVTT files.
   … The Media WG would need to come up with a description of
   WebVTT in our media file format
   … registry that describes initialisation and media segments for
   WebVTT and any other formats we would
   … want to support including TTML.

   cyril: Are the registries specific to a media type or a MIME
   type?
   … The registry deals with ISOBMFF, not audio in ISOBMFF, video
   in ISOBMFF etc.

   eric_carlson: I think that's right

   jer: Yes we're jumping ahead to the second use case,
   … which is delivering captions inside a media container, not
   just as raw payload
   … Not just embedded VTT or TTML, but also 608 and 708 captions,
   which are more commonly found
   … on the web at the moment.
   … Either exposing the raw samples to the client application, so
   an MSE app in a browser would get
   … a callback maybe or an event fired when new samples or
   DataCues (not standardised yet),
   … some packet that describes a thing that happens in the
   timeline,
   … or alternatively, my preference, when MSE encounters timed
   text, turn it directly into captions
   … and turn it into Text Track Cues that are displayable
   natively by the user agent.

   eric_carlson: I agree that's better, but there's always a
   situation where the UA encounters a format
   … it doesn't know how to parse, so we need an escape hatch
   where the page can override the behaviour,
   … or can handle a format that the UA just doesn't know how to
   parse.

   cyril: I fully support that, with a Netflix hat
   … We care about how we display our subtitles and the
   consistency of our subtitles across UAs and devices.
   … I agree sometimes the page wants to let the UA do it,
   … and we have to work with regulation, privacy etc.

   jer: We're bleeding into the interop issue for later about not
   being able to rely on the UA's behaviour

   cyril: You want the page to be able to render the TTML

   eric_carlson: If the page just wants to override the UA
   behaviour, a page could do what
   … many do now, taking the parsed output and do the rendering
   themselves.
   … We have to handle the case where the UA doesn't know how to
   parse.

   Nigel: Is there already an equivalent for audio and video
   formats that the UA doesn't know how to decode?

   eric_carlson: No

   Cyril: The UA processing and performance requirements are a
   different order of magnitude
   … Maybe why there wouldn't be that approach
   … Maybe it could be WebCodecs in the future

   eric_carlson: Thinking about it, the problem I was thinking of
   doesn't make sense, because
   … if the UA doesn't know how to parse the content then it just
   doesn't know, and its the web app
   … that's going to push the data into the parser... No, I take
   that back. If it's muxed content...

   cyril: If it's TTML in MP4, the application will just push it,
   then the TTML gets extracted and
   … passed back to the application at the appropriate time

   eric_carlson: Yes, that's what we need to figure out
   … There isn't an issue where a raw format would be pushed in
   and we need to deal with
   … exposing that to the page somehow.

   jer: A lot of the issues have to do with the MSE specification
   itself.
   … One common way to do ad insertion is to reuse the same source
   buffer and append media from
   … a different source, maybe with a call to changeType() to
   signal the change of codecs.
   … But the MSE API has a requirement that there are always the
   same number and type of tracks,
   … with unchanging identifiers, even if the payload (codec) type
   changes.
   … So if you have a main presentation with two 608 tracks, if
   you wanted to switch midstream to an
   … ad then that would have to have exactly the same number of
   text tracks too, according to MSE.
   … I don't know if the reason for that is still relevant to text
   tracks
   … There may be a need to relax that requirement only for text
   tracks so that you can continue
   … to play without breaking.

   Nigel: I can see UI issues about changes to the user's
   preferred selection

   Jer: Exactly, and how do you present that change to the text
   track

   eric_carlson: We have that in HLS already, it can switch
   rendition to one that has a different set of tracks
   … Nobody has ever complained about it, it could technically be
   a problem

   jer: Good to know how many people choose a specific language
   preference

   gkatsev: That's also for source buffers - for audio and video
   you're not supposed to have gaps,
   … and that's more likely for text tracks, where there may not
   be any for a long time.
   … How does this interact with the Safari experiment with the
   HTML block for rendering?
   … Would this supersede that, or is it independent?

   eric_carlson: In my mind they're separate things.
   … I think this is just an extension of what we already do with
   inband caption tracks
   … where we turn them into WebVTT cues as long as it's a format
   that we understand.
   … We just use the existing text track mechanism.

   eric_carlson: The other problem we need to solve is how to
   signal 608 and 708
   … Technically the init segment has to describe the stream.

   cyril: That is probably an MPEG question
   … A solution is getting published in a couple of months.
   … There will be an amendment to ISOBMFF part 12 that enables
   signalling T35 messages in the init,
   … and you can put as many bytes as you need.
   … I got confused though because 608 is SEI messages not T35
   messages.

   jer: HTML has a side spec called Sourcing Inband Tracks
   … It looks like, to signal 608 or 708 you need to have a trac
   fragment in your moov header.

   <jernoble> [26]https://dev.w3.org/html5/

   html-sourcing-inband-tracks/#mpeg4

     [26] https://dev.w3.org/html5/html-sourcing-inband-tracks/#mpeg4


   cyril: Can we have a forum for this conversation to continue?
   … Is it better in TTWG or MediaWG or somewhere else?

   eric_carlson: I think it would be better to start it here and
   then take it to the MediaWG.
   … Just my quick opinion.

   Nigel: My 15s of thought says the opposite.

   eric_carlson: I think it helps to make progress in a smaller
   group and then take that to a bigger group.

   Nigel: I would say the spec is squarely in MediaWG so I'd
   propose setting up a task force in MediaWG to
   … look at this, and then take the results back up to the wider
   group.
   … Then if there are interested people from here they can join
   that TF.

   Cyril: Need to get the terminology right, useful to do it in a
   task force

   Nigel: someone needs an action to take this task force proposal
   to the chair of the MediaWG

   jernoble: I will take that action

  IMSC

   Nigel: May need to let this topic flow over into a later
   session if we don't have time now

   Pierre: Background: a couple of weeks ago an issue was reported
   by a user of IMSC, a service
   … provider to a large content platform, that their French
   subtitling and captioning team had run
   … into an issue where they couldn't get superscript and
   subscript characters.
   … They turn out to be more important in French than in English
   because France has a
   … governmental organisation that sets standards for the
   language.
   … Those standards say that the abbreviation of first and
   second, like 1er, must be in superscript.
   … Everyone in France understands it if they are not
   superscript, but French standards are to put
   … the ordinal numeral as superscript.
   … So this is a shortcoming of IMSC, evidently.
   … The good news is there's already a TTML2 feature that allows
   super or sub to be specified.
   … Because we have this significant issue and other backlog
   issues it seems like a good time to
   … do a minor revision to IMSC

   cyril: Is there a list?

   pal: Yes, I'll go through it in a few seconds.
   … The intent is a minor revision, and fix this substantial
   issue.
   … I've gone through, and sent an email to the reflector
   yesterday, and taken a stab
   … at labelling the backlog issues that we should try to tackle
   if we are going to embark on this.
   … I labelled this as 1.3 because we're at 1.2 now.
   … There's one big category of backlog issues which are related
   to the results of a liaison with ARIB,
   … a Japanese organisation that have defined a profile of TTML
   for the Japanese broadcast market.
   … Where we left off is we alerted ARIB about 1.1 or 1.2 and got
   suggestions back that require more
   … detailed discussion to make sure we would not do something
   that would not work for them.
   … We never got that collaboration going.
   … Something we should probably do would be to send a
   communication to ARIB saying we are about
   … to start on IMSC1.3, now is the time to have this discussion.
   … Otherwise those issues will stay in the backlog.

   Nigel: Atsushi, do you have any contacts there?

   atsushi: There is NHK, but my main contact in this area has
   moved company, so I need to.
   … establish new contacts. I'm not sure if we should write a
   liaison or make a direct contact.

   Nigel: We can do both

   atsushi: Both would be fine. There stance is not to be too
   responsive generally.

   pal: That's fine, I just don't think we should do anything
   without active collaboration with ARIB.

   atsushi: I understand, yes
   … Let me contact during lunch, if I can, today, some colleagues
   and give me the chance to feed back
   … during the afternoon session.

   pal: If we go ahead we should craft a formal liaison.

   atsushi: Yes, of course.

   pal: In terms of backlog...

   [27]IMSC 1.3 issues

     [27] https://github.com/w3c/imsc/issues?q=is:issue+is:open+label:imsc1.3


   pal: I suggest running through them, and taking notes if there
   are any.
   … [go throughs the list]
   … Super/sub support
   … Factor out HRM
   … Namespace name docs are out of date - not a spec issue, a
   repo issue
   … Editorial bug about the wrong feature being referenced with
   time offset
   … Improve the introduction
   … Improve para wording for WCAG SC 1.1.1
   … was controversial and text is convoluted, time to clean up.

   Pierre: IMSCvnext is prepared for future version, and the same
   as backlog
   … also should be fine to be removed
   … one live feedback on character sets of Japanese
   … some suggestion from APA on description on semantics
   … we should at least ping folks
   … make sure we will pick in next slot
   … following three items, 493, 492, 490, are not blocker, or
   even we can close
   … 489 is errata
   … 484 is super long discussion thread
   … forcedDisplay and visibility hidden, neither anything we can
   do or need to do , but we should again back on this discussion
   … nice to have, but no particular point to have
   … #82, will not touch image profile, unless it is broken

   nigel: it exists and broken already

   pierre: unless somebody have absolute need...

   nigel: serious question, any issue actually impact to image
   profile?

   pierre: three issues pointed above - 493, 492, 490

   nigel: ok to keep open unless touching these three, or
   something need to do?

   pierre: fine to keep open

   nigel: we only update text profile in 1.3, without image
   profile
   … people could use image profile from previous ones like 1.2 or
   even 1.0, it this correct

   pierre: not sure, only objection is working or not, would not
   touch anything more on this unless something happens

   nigel: ok

   pierre: agree on concept, personally, anyway

   nigel: all sound good to me

   pierre: my three requests, one to decide what to proceed,
   create a liaison with ARIB, discussion with APA on 503

   <pal> [28]w3c/imsc#524 (comment)

     [28] https://github.com/w3c/imsc/issues/524#issuecomment-598299006


   [29]Comment regarding APA feedback to resolve

     [29] https://github.com/w3c/imsc/issues/524#issuecomment-598299006


  Next part of the day's meetings

   [30]Joint meeting with APA and MEIG

     [30] https://www.w3.org/events/meetings/5d9bf691-6f90-45b9-9c2a-b89faaedb191/


   Nigel: [temporary adjournement]

  Afternoon session

   Nigel: Welcome everyone to the afternoon session.

    IMSC (continued)

   Pierre: Proposal is to proceed with a minor revision of IMSC
   with the primary objective of addressing the lack of support
   for superscript and subscript
   … and secondarily resolving outstanding editorial and blocking
   issues in the backlog.

   PROPOSAL: Proceed with a minor revision of IMSC as detailed in
   the minutes

   Nigel: Any objections?

   Pierre: Then I think the other one, assuming we go ahead, is to
   get a liaison going to ARIB,
   … a last shot at getting this done.

   PROPOSAL: Liaise with ARIB about feature improvements in IMSC,
   specifically the backlog issues

   Nigel: Any objections to either of the above?

   RESOLUTION: Proceed with a minor revision of IMSC as detailed
   in the minutes

   RESOLUTION: Liaise with ARIB about feature improvements in
   IMSC, specifically the backlog issues

   Nigel: We should think about whether industry needs us to keep
   going with multiple
   … active versions of IMSC or if we can deprecate any of them.
   … Similarly, should we mark it as "allows changes" rather than
   continuing with the version numbering approach.

   Pierre: Good question. If we allow changes, what's the approach
   to removing unused features.

   atsushi: Updateable Recs can accept candidate amendments or
   candidate new features.
   … At any time we can change these candidate changes.
   … Once the candidate changes pass the same procedure as normal
   Rec, including
   … HR, WR, AC Review, everything will be merged into the Rec as
   normative parts of the specification.
   … In theory everything that is similar to CR even if the spec
   is published with a Rec URL.
   … Anything can be done.

   Nigel: So any candidate change can be made, even deprecation or
   removal of features?

   atsushi: Yes

   Pierre: Even those changed versions of the Rec are dated, is
   that right?

   atsushi: Yes the publication date changes, even with candidate
   amendments

   Pierre: Hard to see any reason not to do it

   Nigel: @sideshowbarker and I have been discussing this, there
   are significant markup requirements
   … for the candidate changes, but there is tooling on the way to
   help with that.

   atsushi: I never want to have to do this for TTML!

   Nigel: We can decide about the allows-changes status before we
   go to CR.
   … Any other points on IMSC for us to think about?

   no other points

    WebVTT Interop and issues

   gkatsev: Thanks for coming, I'd love to hear about the WebVTT
   interop stuff

   dana: [Presents slides] Hi, I'm Dana, first TPAC, I work on the
   WebKit team at Apple
   … For some time I've been researching WebVTT and learning about
   the problems with it,
   … why it's not widely used.
   … I'm hear to present what I've learned through my research,
   … and some ideas for making it more attractive for websites to
   use.
   … [slide: Recap of previous years' efforts]
   … Will talk about where we are in the discussion, usage of
   WebVTT in the wild,
   … Web Platform Test interop test results and what they mean,
   … bugs and missing features in WebKit and the WPT
   infrastructure,
   … and then ideas for fixing things.
   … [slide: Recap of previous years' efforts]
   … In previous years we discussed adding a generic text track
   cue class.
   … But important to make sure we're building on something that
   works, i.e. WebVTT.
   … Clear to everyone that WebVTT is not in the state it needs to
   be given it's not widely used.
   … WebVTT rendering is rarely used on high-traffic websites
   … Some sites use WebVTT format, but render cues themselves,
   e.g. Hulu.
   … Suggests rendering is the reason it's unattractive.
   … Problem that sites render it themselves because they don't
   have access to the
   … accessibility features that are only possible through using
   WebVTT.
   … Without using WebVTT, cannot get subtitles in PiP or full
   screen on the iPhone.
   … Users lose out on acccessibility and other features when
   sites use don't use WebVTT.
   … Anecdata: Interop is a problem.
   … WebVTT appears differently on different browsers, so it's not
   reliable.
   … [slide] WPT results
   … Websites tell us they don't like interop of WebVTT between
   browsers.
   … Backed up by results of the test.
   … Rendering scores are critically low.
   … No browser passes >30% of rendering tests.
   … Chrome, Edge and Safari pass <6% of the rendering tests.
   … For the past month I've been going through WebKit's rendering
   test failures,
   … and categorising the bugs.
   … Most are implementation issues,
   … 6 are likely bugs in the tests or the test infrastructure.
   … I'm also new to WebVTT so I could be wrong.
   … This is approximately how it is.
   … I'm planning on filing these issues.
   … We already have them in the WebKit bug database for our own
   tracking purposes.
   … Also planning on posting the 6 test bugs into the WPT repo.
   … [slide] Stand-out bug is accessibility preferences
   … Someone already opened [31]web-platform-tests/wpt#46453
   … Problem is on Mac and iPhone user can set accessibility
   preferences for captions,
   … but the WPT tests don't take those into account, so we fail
   almost all the tests.
   … The default style we apply via our system settings and the
   test infrastructure doesn't know about that.
   … Similar issue in Chrome I beleive.
   … Couple of solutions:
   … 1. Turn off accessibility styling before running tests, in
   the test env.
   … We don't prefer this because we also want to test the
   interaction between user styling and rendering.
   … 2. Add the concept of a cue window to the WebVTT spec.
   … There's discussion about this under the issue.
   … Exposing this concept of a cue window would allow the
   websites to override the system
   … styling of the cue window, which we can then incorporate into
   the tests.
   … We prefer the second solution, to ensure the accessibility.
   … [slide] I also found other issues with the tests.
   … We fail ~80 of them for non-obvious reasons, when it looks to
   me as though the two images
   … are identical or almost identical, maybe differing by
   blurriness, and I'd like to get some help
   … to look into why this is the case.
   … More obvious bugs: inconsistencies between the expected and
   the actual, like border around the video.
   … Those are about 6.
   … The other 35 are webkit bugs we are tracking and dedicating
   time to fixin.
   … [slide] We think the solution to WebVTT interop is first
   filing and testing the bugs in the
   … test infrastructure. We also support proposing a WebVTT focus
   area at Interop 2025,
   … deadline is Oct 9 2024.
   … Would like feedback and suggestions on what a good proposal
   would look like.
   … Even if we are not successful at getting WebVTT into Interop
   2025, we are still committed to fixing
   … out bugs to match WebKit's WebVTT implementation to the spec.
   … We think it's important to the health of the web that pages
   can rely on native subtitle presentation.
   … This would allow for more accessibility features to be
   accessible by users.
   … That's it, thank you!

     [31] https://github.com/web-platform-tests/wpt/issues/46453


   gkatsev: Thank you very much, that was awesome!

   dana: If it's interesting I have the spreadsheet of bugs and
   what it impacts.

   Pierre: Going back to your first slides, these are great
   numbers.
   … Have you also collected numbers on IMSC in the process?

   dana: No, just WebVTT

   pal: Any sense of what the numbers might be for IMSC and TTML?

   dana: No I haven't.

   pal: I think many of the same results exist for IMSC and TTML
   where rendering is done
   … by page code, and the same accessibility challenges exist for
   TTML

   jcraig: Are there WPT tests for TTML?

   gkatsev: No, because it's not natively supported

   jcraig: That would be the first step before doing this

   pal: The same exact issues that you've noted exist for TTML and
   there are some platforms
   … that only use TTML and are forced to use a polyfill or burn
   in after rendering server-side.

   dana: It would be preferable to use WebVTT rather than IMSC to
   make the accessibility features work

   pal: Many of the same considerations apply to both

   gkatsev: Making this a baseline for the future, for HTML
   fragment cues are both methods of getting
   … IMSC support natively, so having really good WebVTT interop
   will allow those to work better also.

   dana: It could sound a little far-fetched imagining a future
   where WebVTT is the most used format.
   … We think this is the first step, to improve interop
   … Makes that future more of a possibility than it is now.

   nigel: I think it's a really good idea to do what you're
   suggesting here to look at higher problem spaces
   … we need to figure out how to make subtitles accessible and
   see how things go from there
   … webvtt interop is a good baseline but there's missing
   features
   … there's things used in practice in ttml that can't be done in
   webvtt
   … there's also format issues like server-side transforms
   … isn't necessarily a good fit for a lot of reasons, speaking
   for the BBC
   … I've definitely seen problems for mapping from ttml into
   webvtt

   <Zakim> jcraig, you wanted to mention FCC requirements for
   captions and to mention WPT, okay to write WPT tests for any
   spec, even if not implemented; allows test-driven development
   and to mention overriding the user styles in the LayoutTest or
   ideally WPT test

   nigel: my vision of an accessible way would be something that
   make it more agnostic from webvtt

   jcraig: Thank you for the presentation, a few points back.

   jcraig: It's ok to write WPT tests for things that have a spec
   … for example include .tentative in the test name
   … It's common to do that for test driven development on the web
   platform.

   <Zakim> jcraig, you wanted to react to nigel

   jcraig: We already have a CI environment that can run those.
   … Additionally, one of the reasons that this test is important
   is that there are FCC
   … requirements, and have been for almost a decade, about
   caption styles,
   … that we support on our platforms, and even games platforms
   support,
   … but I do agree that we should not bypass the accessibility
   settings.
   … There may be some intermediary settings, like Dean Jackson
   had a way to make OS level settings
   … before the test run, and write different tests for different
   OS level settings.
   … Then you can test the rendering part and the customisation
   settings.

   eric_carlson: I think that's an excellent idea.
   … In WebKit's own internal tests we ignore the system styling
   completely.
   … It's a way to have consistent tests.
   … Your idea makes a lot more sense.

   jcraig: Dean's tests were something like reduced motion.

   eric_carlson: I have lots of ideas about how to do it.

   nigel: TTML has large set of test suite, which is not on wpt

   <Zakim> nigel, you wanted to react to nigel to mention IMSC and
   TTML test suites

   <jcraig> jcraig: other tests have been ported to WPT...

   pal: On this issue of WPT tests, how do you create tests that
   there is no way to expose on a web platform?
   … Are you deliberately showing that they're all failing? Is
   that useful?

   jcraig: TTML you want to render in the browser, right?
   … If not then no point in adding to WPT.
   … Not sure how familiar you are, it's a massive CI platform
   that tests every feature on every web platform.
   … It's become the expectation of the place to write the tests
   if they're platform independent.

   pal: I'm a big fan, just not sure if it's useful to write TTML
   tests because they would fail by design.

   jcraig: I wouldn't write a lot of them, just write a base level
   of coverage.

   pal: Not trying to convince anyone, just pointing out that we
   have both in the ecosystem.
   … Until and unless one gets 100% of the market we are going to
   have these issues that were
   … highlighted at the beginning.
   … Two options are:
   … 1. Try to get to agreement to use only one. not worked over
   12 years.
   … 2. Support both, just like there are lots of image codecs
   etc.
   … Until we resolve this issue (note zero objection from me for
   fixing webvtt),
   … we are going to keep having the same issue that you found at
   the beginning.
   … We need to solve the fundamental issue before we get a great
   developer and user experience.
   … Maybe now is not the right time.

   [32]TTML2 test suite (large set of TTML XML files)

     [32] https://github.com/w3c/ttml2-tests


   jcraig: Sounds like no objection to more VTT testing or to
   proposing interop area for Interop 2025,
   … or for fixing the main issues of WebVTT even if it doesn't
   solve the wider long term timed text issues.

   dana: It can't hurt

   gkatsev: I think Interop 2025 would be awesome because it would
   feed back into the spec,
   … and allow us to get to Rec.
   … ON the TTML / IMSC side I think it might be a bit early for
   WPT tests, but with the work
   … on streaming text tracks and html fragment, when that's
   further along, we could write WPT tests
   … for them, especially if part of the use case for that is
   native IMSC support.

   jcraig: Dana, from my experience, I wrote several hundred tests
   last year, you're probably right
   … that there are bugs.

   gkatsev: Definitely bugs, I've seen maybe 10% of tests are
   invalid.

   jcraig: First implementer finds the bugs!

   dana: That would be a goal before interop, that we have a
   functioning test suite.

   nigel: one of the point in testing difficult, approach is by
   design by design
   … use of preference setting is pain
   … last year we discussed and got some responce on this, web
   principle document from TAG
   … observation made by me, use of caption is so wide, these days
   use cases are widely spread
   … not like 20 years ago so can no longer claim that use of
   captions implies disability or vulnerability
   … broder and too many use cases and users exist now, incl.
   disabilities

   <jcraig> The TAG's Design Principles issue Nigel mentioned:
   [33]https://w3ctag.github.io/

   design-principles/#do-not-expose-use-of-assistive-tech

     [33] https://w3ctag.github.io/design-principles/#do-not-expose-use-of-assistive-tech


   nigel: we need to revisit to these for principle design
   … other side, totally different display than native captions
   … we would not get usage data
   … will not get source of data for improvement of us
   … you're harming users allows to gather statistics of use, it
   helps
   … you can only observe on or off for WebVTT
   … not user customisations

   ???: if in specific site, data could be collected

   nigel: talking about is that player page and what is key focus

   Jean-Yves Avenard2: definitely agree that captions are widely
   used now
   … problem with exposing user preference exists
   … anybody customize styles are uniquely identifiable
   … inject large fingerprinting vector
   … absoletely no way to expose

   <gkatsev> s/???2/eric_carlson/

   nigel: if the world changes and allows access to these
   preferences, it cause another side

   cyril: try to give TTML and WebVTT information

   dana: Netflix produces both styles of captions, the vast
   majority that is consumed is TTML.
   … A small amount WebVTT and a small amount image.
   … There's no way for Netflix to migrate to WebVTT short or long
   term that I can see.
   … I'm curious, one of the problems we have with WebVTT, which
   we don't use on the web,
   … even on Safari, is the discrepancy between the Safari support
   vs iOS.
   … If you use Safari you don't get the same results with Core
   Media native playback.
   … Do you have a sense - WPT doesn't test native support, right
   - do you do internal testing?

   jy: They do their testing, we do ours

   eric_carlson: That's something we need to address
   … They don't support CSS etc.

   cyril: The way we use WebVTT in Netflix is lots of p-list
   hooks.
   … Don't even know how to hook those into CSS

   eric_carlson: They do now support CSS in WebVTT files, but they
   don't have a full-blown CSS engine.
   … We can certainly take files that they support and make sure
   that the rendering is the same in
   … WebKit and in Core Media.

   cyril: As a content provider, the choice of WebVTT is not
   obvious because the differences mean we would
   … have to provide 2 versions.

   eric_carlson: I agree that is a problem for us to fix

   jy: Does it matter that there are small differences as long as
   the content is there?

   Cyril: We don't care about pixel accuracy, but for Japanese you
   care about Rubys, vertical text being
   … rendered correctly.
   … Obviously we have positioning requirements to make sure
   captions don't clash with content in the image.
   … If the position is off it's a problem.

   gkatsev: It's about feature support

   pal: I think this is actually the core issue, anecdotal
   evidence I've heard is when a platform goes ahead
   … and tries to use native, and there is native support for TTML
   in a bunch of players, they realise
   … that no two players are the same.
   … Some diffs subtle, then they decide to render themselves.
   … Trying to get to interop is a really good idea.
   … Otherwise folks will continue doing it themselves.

   gkatsev: A couple of years ago a guy (Dan?) at Demuxed talked
   about how and why they decided
   … to render everything themselves. Needing to be FCC compliant
   made them have to render
   … themselves, particularly on set top boxes.
   … Interop2025 would be awesome.
   … My question: do you need anything from us for that?
   … We'd be happy to help, as much as I can, for that.

   dana: No I think...

   eric_carlson: Signals of support, making it clear, I don't know
   how, that if you think it's a good idea
   … that you think it's a good idea with the WPT committee.
   … Coming from the WG would be extremely helpful.

   gkatsev: Is there an existing mechanism for that?

   eric_carlson: I don't know but we'll figure it out and let you
   know.

   jcraig: Typically there are proposals for new focus areas.
   … If the WG agrees, one of the Chairs could just comment in
   that issue.
   … e.g. to say Timed Text supports this.

   dana: When you submit proposals to interop they're on GitHub
   and you can add discussion comments.
   … Once the proposal exists I will share it.

   gkatsev: Can you post it to the timed text mailing list?

   dana: ok

   <jcraig> Current Interop Proposals [34]https://github.com/

   web-platform-tests/interop/issues

     [34] https://github.com/web-platform-tests/interop/issues


   <jcraig> [35]https://github.com/web-platform-tests/interop/

   issues?q=is%3Aissue+is%3Aopen+label%3Afocus-area-proposal

     [35] https://github.com/web-platform-tests/interop/issues?q=is:issue+is:open+label:focus-area-proposal


   gkatsev: I think we're out of time for this topic, technically
   out of time for our scheduled session.

   gkatsev: On the ATTRIBUTES PR, Nigel and I had the question
   about the lang and label and kind
   … interact with the track element.
   … That would be really good to disambiguate.

   [36]new ATTRIBUTES block

     [36] https://github.com/w3c/webvtt/pull/523


    New ATTRIBUTES block [37]w3c/webvtt#523

     [37] https://github.com/w3c/webvtt/issues/523


   github: [38]w3c/webvtt#523

     [38] https://github.com/w3c/webvtt/pull/523


   jcraig: Need to assess, if there's a mismatch, which one wins.
   … I don't have a strong opinion.
   … Main reason we want it in the VTT is sometimes there's no
   HTML as an intermediary,
   … so the track information is missing.

   gkatsev: That makes sense, my question would be would this also
   allow a change in HTML
   … if we're adding precedence to those attributes.

   jcraig: I would expect that whatever we land on, we could have
   the same thing reflected on the track element

   eric_carlson: We also would want to add some text to the spec
   describing the rules of precedence,
   … whichever way we go.

   Nigel: How are you going to work out which way to go?

   eric_carlson: We'll put a stick in the ground and we'll be
   right.

   gkatsev: My assumption is the track element takes precedence

   eric_carlson: That would be right, it would override what's in
   the file.

   gkatsev: Can still have the precedence rules in the VTT spec
   but would also need them in HTML

   eric_carlson: HTML doesn't say anything about how to process
   the contents of the VTT file,
   … so maybe no change needed.

   jcraig: The other editorial suggestions seem fine to me.
   … There was a section question, was just my unfamiliarity with
   bikeshed.

   gkatsev: Should we open an HTML issue now around this to get
   the conversation going.

   jcraig: I'll take that as an action and write it into PR 523 so
   I don't forget it.

   pal: On that last point, if you run into any issues, I can
   help, please don't hesitate to ask.

   jcraig: You mean pushback on HTML?

   pal: Sure, ultimately the question is who writes those tests.
   … As Nigel pointed out there's a large body of tests to port to
   WPT.
   … With reference renderers once we've overcome the issue of
   should we have that at all in WPT,
   … I'm confident that we'll have the resources to make that
   happen.

   group confusion caused because Pierre misheard!

   gkatsev: With that we can, unless there's anything specific to
   WebVTT right now we can end

   SUMMARY: @cookiecrook to raise issue on HTML about track
   attribute precedence

    DAPT

   nigel: my goal is to get agreement or a plan to get DAPT into
   CR
   … we have these 5 open issues

   [shares screen to show DAPT issues]
   … lots of activity lately
   … 4 of these have PRs open for them
   … What I would like to do is go over these PRs and see if
   there's any actions
   … and merge these PRs and do a CfC to request transition to CR
   … which would be subject to group policy, which would be 2
   weeks
   … which would give a change to review the spec as a whole
   … editorial things can be fixed, the substantive things are the
   important bit

   cyril: what if there in a big change?

   nigel: we can do a new CR snapshot

   cyril: the signal is that people can start implementing

   nigel: it triggers a couple of things like starting to do a
   changelog
   … when we met with the APA earlier in the day, it would've been
   helpful to see a changelog
   … and we can share with other HR groups
   … also makes a need for an IR

   atsushi: we need to test but not requirement for CR

   nigel: yes, but needed to leave CR
   … I suggest we have a dapt-tests repo and start putting stuff
   there
   … we already have a repo

   atsushi: you need a link to the IR to pass pub rules
   … can be a stub
   … can be a wiki page

   nigel: we can have a page on the TT wiki

   nigel: start from the oldest

   nigel: we need to request delta reviews for HR

   nigel: the first one [39]dapt#44
   … cyril proposed adding a paragraph note
   … and there's a PR for that addition

     [39] https://github.com/w3c/dapt/issues/44


   there's an approval from me
   … which we can merge unless there are issues

   nigel: next one, [40]dapt#75 define restrictions per script
   type
   … we have a PR for this
   … which has been approved
   … I think there's some changes
   … but they're small
   … if you're in a prerecording script you shouldn't have audio
   recordings
   … and either synthesized or audio recoding
   … I can merge during the break

     [40] https://github.com/w3c/dapt/issues/75


   nigel: the next one [41]dapt#227, quite a big one
   … also a PR, which is approved
   … the idea is to capture metadata for script text to know what
   it represents
   … and we have a top level scriptRepresents and a represents on
   every event tag, which is inherited
   … the exciting bit is the content-descriptor
   … we have a registry of content descriptors
   … hierarchical scheme, like audio, audio:dialogue

     [41] https://github.com/w3c/dapt/issues/227


   cyril: think of it as you have a time text part and you're
   annotating whether the text corresponds to dialog or text on
   screen
   … can be used for translation
   … and produce subtitles files or dubbing script
   … the origin for the info to produce all types of content

   nigel: there's a constraint; if you say a script event has a
   descriptor, but at the document level doesn't include it
   … it's an error

   cyril: document level helps do an early error so there's no
   surprises

   nigel: you can be more specific in script event but if you
   can't use something that wasn't given
   … delimiter is . not ;, so the PR needs a smal update

   nigel: [42]dapt#232, responding to implementation issue where
   people have non DAPT impl files but have smpte times and
   there's not enough info to synchronize
   … we have a PR which introduces some metadata is section D,
   which describes the problem and adds some optional metadata
   … origin timecode, and start of programme timecode
   … if those two are the same they can synchronize
   … if they're different, you can synchronize, but would need
   some work for this
   … and they're completely optional
   … one of the key points is metadata only not intended to be
   used to perform direct synchronization offsets during
   presentations

     [42] https://github.com/w3c/dapt/issues/232


   nigel: last one is [43]dapt#233
   … no proposed change here

     [43] https://github.com/w3c/dapt/issues/233


   cyril: break discussion?

   nigel: can we close with no action?

   cyril: ok, let's do that
   … still discuss it during the break

   nigel: proposal is to merge PR and then go through the admin
   needed to get a working group decision to request transition to
   CR

   cyril: I support that

   atsushi: I also support it

   PROPOSAL: Merge the open Pull Requests and then go through the
   admin needed to get a WG decision to request transition to CR

   RESOLUTION: Merge the open Pull Requests and then go through
   the admin needed to get a WG decision to request transition to
   CR

    Break

  TTML2

   nigel: first thing with TTML2, we've been in CR, the last
   snapshot is 3 years ago
   … we should finish that off
   … what do we need for that?
   … the implementation report
   … shows that the test related to new things we have at least 1
   implementation for most things
   … that means we need a second implementation in order to
   proceed to REC
   … we also have validation tests
   … I'm not sure the best way to have the second passing
   implementation?
   … there are validators out there
   … I don't think we've got any particular spec changes to make
   … one option is to back out some changes
   … we also have some open issues on TTML2 but we have not
   triaged them
   … the easy path is just to do implementations
   … it's more complicated if we want to make new changes
   … because we don't have an active editor
   … does anybody have resource availability?

   pal: what's absolutely blocking and essential?

   nigel: of what?

   pal: all the syntax changes require new tests or not?

   nigel: all of the tests are done

   pal: what's missing?

   cyril: implementations

   nigel: there is one passing implementation

   nigel: there are 2 separate issues
   … as the spec stands right now to take to REC we just need a
   2nd implementation
   … the second problem is if we want to make further changes to
   the spec, we need an editor

   pal: assuming we have the 2nd implementation, do we know of
   changes that are needed?

   nigel: no
   … but I need to do a serious runtrough of the open issues
   … it's not zero work

   pal: my inclination if I would be editor would be ignore
   everything that is not marked as blocking

   nigel: that's fair

   cyril: Reverse question to Pierre's: if we don't get the 2nd
   implementation how can we move the spec forward,
   … if we need to make a new change to TTML2?

   nigel: if we edit a new change in that is substantive
   … we need to write tests and implementations that pass that
   … as it stands we cannot move from CR to REC without second
   implementations

   atsushi: once we have REC, if we need new changes we need WD,
   CR ...
   … we can do another CR with just the changes that have 2
   passing implementations
   … and defer the non-passing tests to a future version

   nigel: most of the ones not passing are validation test
   … for presentation there are audio and body features
   … font embedding family
   … font selection strategy
   … font shear
   … image in body, including png
   … region no default
   … line shear
   … image opacity

   pal: we said we need 2 presentation engines?

   nigel: yes

   pal: for validation, there is a validation tool that can be
   checked and modified
   … the presentation tests are more challenging
   … what was the second implementation for the 1st edition tests?

   nigel: TTPE, IMSC.js or Adhere
   … but at the time we considered validation and presentation as
   2 implementations
   … it was and still is adequate
   … the requirements haven't changed

   pal: ttval is relative easy to update
   … so if ttval was added for both presentation and validation,
   would that be sufficient?

   cyril: not for presentation

   nigel: the audio descriptions would pass

   nigel: the action is to rearrange the table so that for each
   feature you could see if it had a presentation and a validation
   test

   pal: if all we need is a validator implementation, that can be
   done

   cyril: .. in my mind, this is really about getting it done so
   we don't have to think about it anymore

   cyril: The world has moved on without the 2nd implementation,
   and probably without the features at all.

   pal: It's more about standards hygiene

   Nigel: +1

   Cyril: Are there any features in TTML2 required by DAPT?

   Nigel: Good question I need to check.

   Nigel: I will happily nominate Pierre as an editor of TTML2

    TTML2 CR snapshot outdated banner

   Atsushi: Issue about the out of date banner on TTML2 old CR
   snapshot

   [44]TTML2 CR 2020-01-28 with banner

     [44] https://www.w3.org/TR/2020/CR-ttml2-20200128/


   Atsushi: banner points to latest public recommendation but
   after that we have CR
   … The question is what do we want from the Outdated banner?
   … Do we want to point to the latest Rec from /TR/ttml2 or the
   latest publication?
   … or some link to current history.
   … There could be a possibility that everything before the
   latest Rec points to the Rec, and
   … after the published Rec everything points to the latest
   publication.

   Nigel: I think that makes sense, before a Rec point to the Rec
   that follows,
   … and after Rec point to the latest publication.

   atsushi: I will raise this and talk to the systems team about
   it, if that's okay for everyone?

   Cyril: OK sure

   atsushi: I will draft the text and then ask for review on the
   TTWG mailing list.

   pal: Conclusion on TTML2 2nd Edition?

   Nigel: My conclusion was that:
   … 1. Add Pierre as an Editor
   … 2. Encourage folk to work on a 2nd implementation of the
   features that have 1 passing implementation in the IR

   Pierre: We have a blocker on implementation. Doing more work on
   the spec makes that worse

   Nigel: Agree, we shouldn't be addressing issues with feature
   changes unless there's a path to implementation
   … I expect this to be a small editing job, but the focus should
   be on implementation

   Pierre: Happy to edit, but contingent on their being focus on
   implementation
   … We need to have resources, people committing to
   implementation work

   Nigel: I agree, otherwise it's a waste of time
   … We all need to consider whether we have resource to commit.
   Let's come back to it in a month's time
   … I won't do anything about adding you as editor, for the time
   being

    TTML Media Type Definition and Profile

   Nigel: This document is good. It's a Note, but since we
   published it, the Process now has a Registry document type
   … Should we leave this as is, or formally make it a Registry?
   … In general, I want to do as little as possible with it
   … And, given we've done work to create a boilerplate for
   Registries, it might make sense to move this to the Registry
   track
   … Atsushi, can we turn a Note into a Registry and keep the same
   shortname?

   Atsushi: Some Registries are still published as draft Notes, It
   should be possible
   … Need to check the procedure for publishing as a first draft
   … Reusing the same shortname should be fine

   Nigel: So I propose to do the work needed to turn this into a
   Registry Track document. No commitment to how soon, though

   Cyril: We need an identifier for DAPT, so we'll need to update
   it. That could be a good incentive to do it, if we'd be blocked

   Nigel: I don't think we would, it's more a hygiene issue

   cpn: We've done this in Media WG, we have standalone Registries
   and Francois has done
   … the work to set up the auto publication

   atsushi: Coding systems?

   cpn: Yes, they were Notes and we moved them over - WebCodecs
   and MSE Bytestream Formats

   Nigel: Anything else on the Profile Registry?

   (nothing)

    Joint meeting follow-ups

   Nigel: We had 3 joint meetings this week
   … Monday was MEIG, talked about DAPT, and there was interest in
   that. Wolfgang expressed interest in writing implementation to
   convert DAPT to next-generation audio
   … We talked about adding text tracks to MSE. MSE supports audio
   and video, not subtitles and captions
   … There was no negative reaction, some support. We then took it
   to Media WG on Thursday, and it was more positive
   … I filed an issue to add it. There were technical questions
   raised, to be answered.
   … Things like switching the number of tracks available when you
   go to an advert
   … There's currently a requirement to have the same number of
   tracks, but a different set of text tracks might be available
   … Today we had joint meeting with APA WG. That was generally
   positive as well

   Gary: Something mentioned in APA was symbolics, could result in
   text track additions

   Nigel: Relates to not being able to have markup in text content
   in TTML
   … Media Session only supports a plain text chapter title, no
   markup. So no way to embed left-to-right. It's a more general
   problem

   Gary: WIth Media Session, would we want it to start using the
   chapters kind?
   … We'd want to make sure the caption formats can add the
   symbolics information

   Chris: Does getting symbolics into Unicode become a
   requirement?

   Nigel: There may not be agreement that it belongs in Unicode

  Conclusion

   Nigel: Thank you all for your contributions. We covered all the
   agenda, success!
   … We meet next on Thursday 10 October

   [adjourned]

Summary of resolutions

    1. [45]Proceed with a minor revision of IMSC as detailed in
       the minutes
    2. [46]Liaise with ARIB about feature improvements in IMSC,
       specifically the backlog issues
    3. [47]Merge the open Pull Requests and then go through the
       admin needed to get a WG decision to request transition to
       CR


    Minutes manually created (not a transcript), formatted by
    [48]scribe.perl version 229 (Thu Jul 25 08:38:54 2024 UTC).

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

Received on Saturday, 28 September 2024 00:56:58 UTC