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