IRC log of tt on 2020-06-11

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Meeting: Timed Text Working Group Teleconference
14:58:26 [nigel]
scribe: nigel
14:58:33 [nigel]
present: Nigel
14:58:52 [nigel]
Regrets: Andreas, Cyril
14:58:57 [nigel]
Previous meeting: https://www.w3.org/2020/06/04-tt-minutes.html
14:59:12 [nigel]
Chair: Nigel, Gary
15:01:10 [atsushi]
present+
15:02:49 [pal]
pal has joined #tt
15:03:00 [gkatsev]
present+ Gary
15:03:16 [nigel]
Present+ Pierre
15:03:28 [nigel]
Topic: This meeting
15:03:56 [nigel]
Nigel: I think we'll pass over TTML2 2nd Ed IR because I don't think there's anything to discuss.
15:04:09 [nigel]
.. We have some IMSC issues to cover
15:04:16 [nigel]
.. I think that's it. Any other business?
15:04:27 [nigel]
Pierre: Most important thing is managing the PING review of TTML2.
15:04:35 [nigel]
Nigel: Good point, let's agenda+ that.
15:05:37 [nigel]
Gary: Also if we have time the WebVTT headers issue
15:06:35 [nigel]
Nigel: Thanks, those both agenda+ now. Any more?
15:07:02 [nigel]
Topic: TTML2 Add consideration for font fingerprinting.
15:07:17 [nigel]
github: https://github.com/w3c/ttml2/issues/1202
15:07:44 [nigel]
Nigel: The status is the PR was merged before a response from the PING folk who raised
15:07:58 [nigel]
.. the issue, to my question asking for their comments on the TTWG's resolutions last week.
15:08:59 [nigel]
.. It's also clear from @samweiler's comments that he would far prefer a normative statement.
15:09:29 [nigel]
.. The impact of that would be that we would have to change the section the text is in
15:09:40 [nigel]
.. to be normative, and that we should have some kind of test for it.
15:09:44 [nigel]
.. That's my current reading.
15:10:10 [nigel]
Pierre: I think we need to step back and meet with PING or really have a discussion about
15:10:16 [nigel]
.. what the end objective is here.
15:10:33 [nigel]
.. Is it to have a running list of potential privacy issues that get updated as new ones come
15:10:36 [nigel]
.. up every new edition?
15:10:40 [nigel]
.. Is it for a definitive list today?
15:10:49 [nigel]
.. Is it to anticipate all potential mitigations?
15:11:02 [nigel]
.. If we don't figure out the objective then we won't get to a conclusion.
15:11:11 [nigel]
.. I sense that PING is trying to do something and I don't understand what that is.
15:11:35 [nigel]
.. We need to step back. I think it is a bad idea to accept what they propose, but if we do,
15:11:41 [nigel]
.. and then something else comes up, we're back to square 1.
15:12:08 [nigel]
.. I think we, especially the Chairs and Editors, and I'm happy to help because of IMSC,
15:12:14 [nigel]
.. need to clarify the objective with PING.
15:12:24 [nigel]
Nigel: Enumerating our options:
15:12:54 [nigel]
.. 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.
15:13:19 [nigel]
.. 2. Change as per the request and deal with probably objections from within the TTWG.
15:13:44 [nigel]
.. 3. Try to discuss more with PING and understand if there are other acceptable approaches from their perspective.
15:13:51 [nigel]
.. Any others?
15:14:06 [nigel]
Pierre: On the 2nd one, it's not only dealing with conflict within this WG. To me the biggest
15:14:18 [nigel]
.. risk is what will happen next? We have to find a way to deal with those comments in the
15:14:21 [nigel]
.. long run I think.
15:14:37 [nigel]
.. In the case of accessibility, the situation is a lot clearer because the accessibility group
15:14:49 [nigel]
.. has created a detailed document. We largely reference it and provide an interpretation
15:14:56 [nigel]
.. of the requirements in that document within ours.
15:15:09 [nigel]
.. That was extremely helpful when it came to the question of color contrast because
15:15:24 [nigel]
.. we were able to go back to the APA document and argue about the requirements that
15:15:28 [nigel]
.. were written. That really helped.
15:15:40 [nigel]
.. Here we don't have that, we just have one comment on one vulnerability on one document.
15:15:47 [nigel]
.. It is very hard to address those comments in isolation.
15:16:12 [nigel]
Nigel: I note you're raising the stakes within W3C beyond TTWG there?
15:16:25 [nigel]
Pierre: No, my concern with accepting their proposal verbatim, setting aside the impact
15:16:37 [nigel]
.. on the process, which we could waive, and may result in an objection to override, which
15:16:48 [nigel]
.. are already super annoying, but the 3rd part, accepting this one comment, does not
15:16:59 [nigel]
.. provide a good template for future comments and how to work with the PING in the long run.
15:17:16 [nigel]
.. For example we don't have clarity about whether they are individuals or the PING itself
15:17:22 [nigel]
.. commenting.
15:19:20 [nigel]
Nigel: Putting this another way entirely, we could say that the open-endedness of this is
15:19:35 [nigel]
.. due in part to the lack of defined semantics for resource fetching in TTML2, and that
15:19:51 [nigel]
.. we could tighten that up and clarify the extent of any vulnerabilities by specifying those
15:19:56 [nigel]
.. resource fetching semantics.
15:20:08 [nigel]
Pierre: I think that's what we're doing by deferring normative changes to a later edition.
15:21:27 [nigel]
Nigel: We have another big challenge with specifying such fetch semantics is that the
15:21:39 [nigel]
.. context of use of TTML and its resources is too broad. If external resources are provided
15:21:52 [nigel]
.. as part of some sort of multiplexed stream of data, there may be no remote fetching
15:22:11 [nigel]
.. at all, but we still would allow for referencing of resources external to the TTML document.
15:22:19 [nigel]
.. So we can't straightforwardly solve this.
15:22:46 [nigel]
Pierre: Yes, my biggest concern, is trying to solve these very complex problems at the
15:22:50 [nigel]
.. last minute, normatively.
15:23:16 [nigel]
.. I think if we say we will tackle them in the next edition, we will do it. We generally do,
15:23:20 [nigel]
.. when we make a commitment like this.
15:23:41 [nigel]
Nigel: It might be really hard, and take a long time.
15:23:51 [nigel]
Pierre: It is completely independent in a sense. It is system dependent.
15:25:11 [nigel]
Nigel: What to do?
15:25:43 [nigel]
.. I think we should do nothing and wait. We don't have a transition request to PR imminent,
15:25:50 [nigel]
.. because we have work to do on the IR.
15:26:04 [nigel]
.. This gives a chance for PING to respond, and if they do not, then when we do get round
15:26:18 [nigel]
.. to making the transition request, we can explain the situation and take silence as assent.
15:26:36 [nigel]
Pierre: Does this block IMSC 1.2 because it references TTML2 2nd Ed?
15:26:52 [nigel]
Nigel: Surprisingly, no, W3C accepts, rightly or wrongly, normative references to CRs
15:26:56 [nigel]
.. these days.
15:27:30 [nigel]
.. If we reverted the references to 1st Ed then we would not have addressed the PING and
15:27:47 [nigel]
.. security comments against IMSC 1.2 which were delegated to TTML2 2nd Ed.
15:28:11 [nigel]
.. I get the sense there's a bit of a house of cards here and it could get blocked.
15:28:22 [nigel]
Pierre: I recommend that we pro-actively tell PING this is a complex issue that we don't
15:28:39 [nigel]
.. think can be solved adequately at PR, and we intend to solve it with them in the next edition.
15:28:57 [nigel]
Nigel: No arguments from me about trying to work more closely with them.
15:29:44 [nigel]
SUMMARY: Action for @nigelmegitt to go back to PING and explain the situation and request further collaboration
15:29:47 [nigel]
Pierre: I'm happy to help.
15:30:23 [nigel]
Topic: IMSC 1.2 Transition Request to PR
15:30:50 [nigel]
Atsushi: We hope it will be approved tomorrow and the next publication slot is Tuesday
15:31:04 [nigel]
.. 16th June, so I plan to work on that for publication on 16th June.
15:31:22 [nigel]
Nigel: That's great news. Are any changes needed, do you need any Editor's help?
15:31:34 [nigel]
Atsushi: Date of publication is all I think. I can edit it locally, but that might be required
15:31:36 [nigel]
.. for merging.
15:31:47 [nigel]
Nigel: That seems trivial?
15:31:59 [nigel]
Pierre: Yes, when we're sure please file an issue on the PR and I'll fix it of course.
15:32:07 [nigel]
.. I have bad track record guessing!
15:32:24 [nigel]
Atsushi: I think the final decision will be made around mid-afternoon East Coast US time
15:32:55 [nigel]
.. tomorrow so let me work on this on Saturday following a status change of the transition
15:32:58 [nigel]
.. request.
15:33:05 [nigel]
Nigel: That's great, thank you.
15:33:47 [nigel]
Topic: [WR/ARIB] Compatibility with ARIB-TTML / 5. Additional style control imsc#550
15:33:52 [nigel]
github: https://github.com/w3c/imsc/issues/550
15:35:09 [nigel]
Nigel: I commented that I think some analysis could be helpful. Any other thoughts?
15:35:18 [nigel]
Pierre: I have not had time to carefully study that one.
15:35:40 [nigel]
.. On letter spacing, I have actually had the opportunity to spend a lot of time on it.
15:35:56 [nigel]
.. My understanding is that the exact same issue is present in digital cinema.
15:36:11 [nigel]
.. Letter spacing is really important in all languages. The practice, in DC, is not to handle
15:36:25 [nigel]
.. letter spacing in the font file itself, but to handle it at the markup level. I do not know why.
15:36:43 [nigel]
.. Japanese cinema subtitles also allow precise letter spacing. This was a feature requested
15:36:49 [nigel]
.. for TTML2 and ultimately rejected.
15:37:03 [nigel]
.. The author will adjust kerning while authoring in their tool, and this will be reflected in
15:37:15 [nigel]
.. the markup. I have asked many times why this couldn't be done in the font, especially
15:37:26 [nigel]
.. since in the case of cinema a dedicated font file is provided with Japanese subtitles.
15:37:31 [nigel]
.. I have never received an answer.
15:37:44 [nigel]
.. I could understand if you could not provide a font file, I would say okay, it has to be
15:37:59 [nigel]
.. handled as part of the markup, but if a bespoke font file is provided why not use that.
15:38:32 [nigel]
Nigel: Do you know if there is a use case for different kerning between the same characters
15:38:38 [nigel]
.. in different parts of the same presentatoin?
15:38:41 [nigel]
s/oin/ion
15:38:49 [nigel]
Pierre: I did ask precisely that and did not get an answer.
15:39:45 [nigel]
Gary: I wonder if this is partially something to do with direction of text, where particularly
15:39:57 [nigel]
.. in Japanese you want to adjust it more because if you adjust it one way then the other
15:40:09 [nigel]
.. way will be wrong, too large or too small. I'm not sure how often that is actually the case
15:40:15 [nigel]
.. for captions but it could happen on the web.
15:40:32 [nigel]
Nigel: Is there CSS for this?
15:40:40 [nigel]
Gary: Yes, letter-spacing property
15:40:48 [nigel]
.. It just takes a length
15:41:06 [nigel]
Nigel: In the context of the web, specifying this is current practice.
15:41:53 [nigel]
.. It's in CSS 1, SVG, CSS 2.1. There's also font-kerning, which sets the use of the kerning
15:41:58 [nigel]
.. information held within the font.
15:42:12 [nigel]
.. That's in CSS Fonts Level 3 CR
15:42:40 [nigel]
.. I don't remember why we rejected this in TTML2.
15:43:22 [nigel]
Pierre: [looks for it] It's #52.
15:43:25 [nigel]
Nigel: Also #118
15:44:11 [nigel]
Nigel: I see #52 came from the tracker, was raised there by Pierre and originated in a SMPTE liaison.
15:44:39 [nigel]
.. And then #118 was also from the tracker, raised by Glenn, and originated in ARIB-TT.
15:44:51 [nigel]
.. So we have seen this before, but there's no record of it.
15:46:24 [nigel]
.. I see that we did add tts:letterSpacing! So this is resolved.
15:47:04 [nigel]
Pierre: Please correct my earlier statement - letterSpacing is in TTML2.
15:47:23 [nigel]
Nigel: Now what I want to know is what is different about ARIB-TT's letter spacing from what
15:47:30 [nigel]
.. we have in TTML2?
15:48:19 [nigel]
SUMMARY: More work needed to understand any semantic differences between similar features in ARIB-TT and TTML2
15:49:06 [nigel]
Topic: Where should "headers" go relative to the `WEBVTT` magic string? webvtt#485
15:49:11 [nigel]
github: https://github.com/w3c/webvtt/issues/485
15:49:47 [nigel]
Gary: HLS has a concept of segmented WebVTT.
15:50:01 [nigel]
.. To be able to display them properly they added a TIMESTAMP-MAP that maps the
15:50:08 [nigel]
.. WebVTT times to the HLS timeline.
15:50:20 [nigel]
.. The HLS spec refers to "WebVTT Header" for specifying this timestamp map.
15:50:39 [nigel]
.. The problem was that an issue was opened for supporting TIMESTAMP-MAP in a place
15:51:02 [nigel]
.. and the question was "what are WebVTT headers?" because the current specification no
15:51:05 [nigel]
.. longer includes that concept.
15:51:16 [nigel]
.. A long time ago regions were specified in WebVTT headers but it was removed.
15:51:29 [nigel]
.. What prompted this was a question about if the header can be on the same line as the
15:51:35 [nigel]
.. WEBVTT marker or whether it is on a new line.
15:51:59 [nigel]
.. Then they also opened a question with IETF about amending the HLS RFC that refers to
15:52:01 [nigel]
.. WebVTT header.
15:52:33 [nigel]
Nigel: I added a comment because I think it is not obvious where the best place is to fix
15:52:38 [nigel]
.. this: in the HLS spec or in WebVTT.
15:52:54 [nigel]
Gary: Yes. WebVTT spec, aside, it's a bit tricky because if WebVTT doesn't use headers
15:53:04 [nigel]
.. itself it seems a bit weird to have a definition that the spec doesn't use.
15:53:13 [nigel]
.. But maybe that's fine because HLS and other things may refer to these headers.
15:53:29 [nigel]
.. Or, maybe more future work, there are some feature requests and enhancements for
15:53:40 [nigel]
.. WebVTT like adding metadata, that could be implemented as headers.
15:53:48 [nigel]
.. If we think of it as step 1 toward that, maybe that's fine.
15:54:13 [nigel]
Nigel: Why was it removed, only because it was no longer being used?
15:54:26 [nigel]
Gary: It sounds like regions were translated to be blocks, and then the syntax of headers
15:54:37 [nigel]
.. was unclear so it was removed instead of specifying it because no other feature was
15:54:39 [nigel]
.. using it.
15:55:00 [nigel]
Nigel: Is there any usage data about the syntax of files that use these headers?
15:55:13 [nigel]
Gary: It is very common in HLS, maybe all segmented WebVTT in HLS has this header.
15:55:40 [gkatsev]
-> https://github.com/w3c/webvtt/issues/304 issue that triggered removal of headers from webvtt
15:55:43 [nigel]
Nigel: It feels like it would be appropriate for Apple to make a proposal here, as key
15:55:48 [nigel]
.. proponents of both HLS and WebVTT.
15:56:29 [nigel]
Gary: I'm not sure what the best approach is here.
15:57:01 [nigel]
.. I did have one other proposal, which is to grab the WebVTT header text and publish
15:57:14 [nigel]
.. it separately as a WG Note, and punt on updating the spec itself until a later date.
15:57:20 [nigel]
.. I don't know if it is worth doing.
15:57:36 [nigel]
Nigel: And in that proposal it wouldn't be referenced by anything?
15:57:49 [nigel]
Gary: Right, but it would be slightly more official than looking at an old version of the spec.
15:58:11 [nigel]
Nigel: Does the RFC have a dated reference to WebVTT?
15:58:38 [nigel]
.. Oh, it is the Draft CG Report.
15:58:44 [nigel]
-> https://w3c.github.io/webvtt/ Reference from HLS
15:58:53 [nigel]
Gary: It does have a date associated with it.
15:59:10 [nigel]
.. June 2017. But the link references the github.io version which is basically the latest.
16:00:18 [nigel]
SUMMARY: Discussions continuing, further inputs welcome.
16:00:42 [nigel]
Topic: [WR/ARIB] Compatibility with ARIB-TTML / 5. Additional style control imsc#550 [continued]
16:00:50 [nigel]
github: https://github.com/w3c/imsc/issues/550
16:01:04 [nigel]
Pierre: I recall that letter spacing is not supposed to be used on a character by character basis.
16:01:18 [nigel]
.. ipd is supposed to allow character by character adjustment, and it is specified not to be
16:01:36 [nigel]
.. negative in TTML2. So I'm 99% certain that the ARIB-TT feature maps to ipd not letterSpacing.
16:01:52 [nigel]
.. We need to study this in more detail but I wanted to add this for the record.
16:03:11 [nigel]
Topic: Meeting close
16:03:24 [nigel]
Nigel: Thanks everyone [adjourns meeting]
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.. some.test/url/to/test/scribescript
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rrsagent, make minutes v2
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I have made the request to generate https://www.w3.org/2020/06/11-tt-minutes.html nigel
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s|some.test/url/to/test/scribescript||
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rrsagent, make minutes v2
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I have made the request to generate https://www.w3.org/2020/06/11-tt-minutes.html nigel
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s/ //
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scribeOptions: -final -noEmbedDiagnostics
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zakim, end meeting
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As of this point the attendees have been Nigel, atsushi, Gary, Pierre
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RRSAgent, please draft minutes v2
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I have made the request to generate https://www.w3.org/2020/06/11-tt-minutes.html Zakim
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I am happy to have been of service, nigel; please remember to excuse RRSAgent. Goodbye
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Zakim has left #tt
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Agenda: https://github.com/w3c/ttwg/issues/121
16:21:56 [nigel]
rrsagent, make minutes v2
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I have made the request to generate https://www.w3.org/2020/06/11-tt-minutes.html nigel
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rrsagent, excuse us
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I see no action items