Meeting minutes
This meeting
Nigel: I think we'll pass over TTML2 2nd Ed IR because I don't think there's anything to discuss.
… We have some IMSC issues to cover
… I think that's it. Any other business?
Pierre: Most important thing is managing the PING review of TTML2.
Nigel: Good point, let's agenda+ that.
Gary: Also if we have time the WebVTT headers issue
Nigel: Thanks, those both agenda+ now. Any more?
TTML2 Add consideration for font fingerprinting.
github: https://github.com/w3c/ttml2/issues/1202
Nigel: The status is the PR was merged before a response from the PING folk who raised
… the issue, to my question asking for their comments on the TTWG's resolutions last week.
… It's also clear from @samweiler's comments that he would far prefer a normative statement.
… The impact of that would be that we would have to change the section the text is in
… to be normative, and that we should have some kind of test for it.
… That's my current reading.
Pierre: I think we need to step back and meet with PING or really have a discussion about
… what the end objective is here.
… Is it to have a running list of potential privacy issues that get updated as new ones come
… up every new edition?
… Is it for a definitive list today?
… Is it to anticipate all potential mitigations?
… If we don't figure out the objective then we won't get to a conclusion.
… I sense that PING is trying to do something and I don't understand what that is.
… We need to step back. I think it is a bad idea to accept what they propose, but if we do,
… and then something else comes up, we're back to square 1.
… I think we, especially the Chairs and Editors, and I'm happy to help because of IMSC,
… need to clarify the objective with PING.
Nigel: Enumerating our options:
… 1. Keep as is and when making the transition request to PR, note the lack of conclusion to this HR review, assuming it has not been resolved.
… 2. Change as per the request and deal with probably objections from within the TTWG.
… 3. Try to discuss more with PING and understand if there are other acceptable approaches from their perspective.
… Any others?
Pierre: On the 2nd one, it's not only dealing with conflict within this WG. To me the biggest
… risk is what will happen next? We have to find a way to deal with those comments in the
… long run I think.
… In the case of accessibility, the situation is a lot clearer because the accessibility group
… has created a detailed document. We largely reference it and provide an interpretation
… of the requirements in that document within ours.
… That was extremely helpful when it came to the question of color contrast because
… we were able to go back to the APA document and argue about the requirements that
… were written. That really helped.
… Here we don't have that, we just have one comment on one vulnerability on one document.
… It is very hard to address those comments in isolation.
Nigel: I note you're raising the stakes within W3C beyond TTWG there?
Pierre: No, my concern with accepting their proposal verbatim, setting aside the impact
… on the process, which we could waive, and may result in an objection to override, which
… are already super annoying, but the 3rd part, accepting this one comment, does not
… provide a good template for future comments and how to work with the PING in the long run.
… For example we don't have clarity about whether they are individuals or the PING itself
… commenting.
Nigel: Putting this another way entirely, we could say that the open-endedness of this is
… due in part to the lack of defined semantics for resource fetching in TTML2, and that
… we could tighten that up and clarify the extent of any vulnerabilities by specifying those
… resource fetching semantics.
Pierre: I think that's what we're doing by deferring normative changes to a later edition.
Nigel: We have another big challenge with specifying such fetch semantics is that the
… context of use of TTML and its resources is too broad. If external resources are provided
… as part of some sort of multiplexed stream of data, there may be no remote fetching
… at all, but we still would allow for referencing of resources external to the TTML document.
… So we can't straightforwardly solve this.
Pierre: Yes, my biggest concern, is trying to solve these very complex problems at the
… last minute, normatively.
… I think if we say we will tackle them in the next edition, we will do it. We generally do,
… when we make a commitment like this.
Nigel: It might be really hard, and take a long time.
Pierre: It is completely independent in a sense. It is system dependent.
Nigel: What to do?
… I think we should do nothing and wait. We don't have a transition request to PR imminent,
… because we have work to do on the IR.
… This gives a chance for PING to respond, and if they do not, then when we do get round
… to making the transition request, we can explain the situation and take silence as assent.
Pierre: Does this block IMSC 1.2 because it references TTML2 2nd Ed?
Nigel: Surprisingly, no, W3C accepts, rightly or wrongly, normative references to CRs
… these days.
… If we reverted the references to 1st Ed then we would not have addressed the PING and
… security comments against IMSC 1.2 which were delegated to TTML2 2nd Ed.
… I get the sense there's a bit of a house of cards here and it could get blocked.
Pierre: I recommend that we pro-actively tell PING this is a complex issue that we don't
… think can be solved adequately at PR, and we intend to solve it with them in the next edition.
Nigel: No arguments from me about trying to work more closely with them.
SUMMARY: Action for @nigelmegitt to go back to PING and explain the situation and request further collaboration
Pierre: I'm happy to help.
IMSC 1.2 Transition Request to PR
Atsushi: We hope it will be approved tomorrow and the next publication slot is Tuesday
… 16th June, so I plan to work on that for publication on 16th June.
Nigel: That's great news. Are any changes needed, do you need any Editor's help?
Atsushi: Date of publication is all I think. I can edit it locally, but that might be required
… for merging.
Nigel: That seems trivial?
Pierre: Yes, when we're sure please file an issue on the PR and I'll fix it of course.
… I have bad track record guessing!
Atsushi: I think the final decision will be made around mid-afternoon East Coast US time
… tomorrow so let me work on this on Saturday following a status change of the transition
… request.
Nigel: That's great, thank you.
[WR/ARIB] Compatibility with ARIB-TTML / 5. Additional style control imsc#550
github: https://github.com/w3c/imsc/issues/550
Nigel: I commented that I think some analysis could be helpful. Any other thoughts?
Pierre: I have not had time to carefully study that one.
… On letter spacing, I have actually had the opportunity to spend a lot of time on it.
… My understanding is that the exact same issue is present in digital cinema.
… Letter spacing is really important in all languages. The practice, in DC, is not to handle
… letter spacing in the font file itself, but to handle it at the markup level. I do not know why.
… Japanese cinema subtitles also allow precise letter spacing. This was a feature requested
… for TTML2 and ultimately rejected.
… The author will adjust kerning while authoring in their tool, and this will be reflected in
… the markup. I have asked many times why this couldn't be done in the font, especially
… since in the case of cinema a dedicated font file is provided with Japanese subtitles.
… I have never received an answer.
… I could understand if you could not provide a font file, I would say okay, it has to be
… handled as part of the markup, but if a bespoke font file is provided why not use that.
Nigel: Do you know if there is a use case for different kerning between the same characters
… in different parts of the same presentation?
Pierre: I did ask precisely that and did not get an answer.
Gary: I wonder if this is partially something to do with direction of text, where particularly
… in Japanese you want to adjust it more because if you adjust it one way then the other
… way will be wrong, too large or too small. I'm not sure how often that is actually the case
… for captions but it could happen on the web.
Nigel: Is there CSS for this?
Gary: Yes, letter-spacing property
… It just takes a length
Nigel: In the context of the web, specifying this is current practice.
… It's in CSS 1, SVG, CSS 2.1. There's also font-kerning, which sets the use of the kerning
… information held within the font.
… That's in CSS Fonts Level 3 CR
… I don't remember why we rejected this in TTML2.
Pierre: [looks for it] It's #52.
Nigel: Also #118
Nigel: I see #52 came from the tracker, was raised there by Pierre and originated in a SMPTE liaison.
… And then #118 was also from the tracker, raised by Glenn, and originated in ARIB-TT.
… So we have seen this before, but there's no record of it.
… I see that we did add tts:letterSpacing! So this is resolved.
Pierre: Please correct my earlier statement - letterSpacing is in TTML2.
Nigel: Now what I want to know is what is different about ARIB-TT's letter spacing from what
… we have in TTML2?
SUMMARY: More work needed to understand any semantic differences between similar features in ARIB-TT and TTML2
Where should "headers" go relative to the `WEBVTT` magic string? webvtt#485
github: https://github.com/w3c/webvtt/issues/485
Gary: HLS has a concept of segmented WebVTT.
… To be able to display them properly they added a TIMESTAMP-MAP that maps the
… WebVTT times to the HLS timeline.
… The HLS spec refers to "WebVTT Header" for specifying this timestamp map.
… The problem was that an issue was opened for supporting TIMESTAMP-MAP in a place
… and the question was "what are WebVTT headers?" because the current specification no
… longer includes that concept.
… A long time ago regions were specified in WebVTT headers but it was removed.
… What prompted this was a question about if the header can be on the same line as the
… WEBVTT marker or whether it is on a new line.
… Then they also opened a question with IETF about amending the HLS RFC that refers to
… WebVTT header.
Nigel: I added a comment because I think it is not obvious where the best place is to fix
… this: in the HLS spec or in WebVTT.
Gary: Yes. WebVTT spec, aside, it's a bit tricky because if WebVTT doesn't use headers
… itself it seems a bit weird to have a definition that the spec doesn't use.
… But maybe that's fine because HLS and other things may refer to these headers.
… Or, maybe more future work, there are some feature requests and enhancements for
… WebVTT like adding metadata, that could be implemented as headers.
… If we think of it as step 1 toward that, maybe that's fine.
Nigel: Why was it removed, only because it was no longer being used?
Gary: It sounds like regions were translated to be blocks, and then the syntax of headers
… was unclear so it was removed instead of specifying it because no other feature was
… using it.
Nigel: Is there any usage data about the syntax of files that use these headers?
Gary: It is very common in HLS, maybe all segmented WebVTT in HLS has this header.
<gkatsev> issue that triggered removal of headers from webvtt
Nigel: It feels like it would be appropriate for Apple to make a proposal here, as key
… proponents of both HLS and WebVTT.
Gary: I'm not sure what the best approach is here.
… I did have one other proposal, which is to grab the WebVTT header text and publish
… it separately as a WG Note, and punt on updating the spec itself until a later date.
… I don't know if it is worth doing.
Nigel: And in that proposal it wouldn't be referenced by anything?
Gary: Right, but it would be slightly more official than looking at an old version of the spec.
Nigel: Does the RFC have a dated reference to WebVTT?
… Oh, it is the Draft CG Report.
Gary: It does have a date associated with it.
… June 2017. But the link references the github.io version which is basically the latest.
SUMMARY: Discussions continuing, further inputs welcome.
[WR/ARIB] Compatibility with ARIB-TTML / 5. Additional style control imsc#550 [continued]
github: https://github.com/w3c/imsc/issues/550
Pierre: I recall that letter spacing is not supposed to be used on a character by character basis.
… ipd is supposed to allow character by character adjustment, and it is specified not to be
… negative in TTML2. So I'm 99% certain that the ARIB-TT feature maps to ipd not letterSpacing.
… We need to study this in more detail but I wanted to add this for the record.
Meeting close
Nigel: Thanks everyone [adjourns meeting]
…