15:01:18 RRSAgent has joined #tt 15:01:18 logging to https://www.w3.org/2021/06/10-tt-irc 15:01:21 RRSAgent, make logs Public 15:01:23 Meeting: Timed Text Working Group Teleconference 15:01:51 scribe: nigel 15:01:55 Present: Nigel 15:02:00 Regrets: Andreas, Glenn 15:02:10 Agenda: https://github.com/w3c/ttwg/issues/187 15:02:27 Previous meeting: https://www.w3.org/2021/05/27-tt-minutes.html 15:03:38 Present+ Cyril 15:05:10 Present+ Pierre, Gary 15:06:44 Present+ Atsushi 15:07:00 Topic: This meeting 15:07:33 Nigel: Lots to get through today. 15:07:53 .. TTML2 open issues, 15:08:01 .. IMSC HRM issues, 15:08:08 .. and an IMSC Tests issue 15:08:20 .. For AOB there's TPAC 2021 - anything else? 15:08:38 group: [no other business] 15:08:58 Topic: Shear calculations and origin of coordinate system. w3c/ttml2#1199 15:09:10 github: https://github.com/w3c/ttml2/issues/1199 15:09:36 Nigel: Glenn informed me earlier today that he is planning to open a pull request to address this, and is doing implementation work. 15:09:51 .. I asked him to share his thoughts on the issue before opening the pull request, and he said he would. 15:10:18 .. He summarised it as "don't optimise too soon", which I think means "you don't have to implement the ideal end result". 15:10:34 .. I'm interested to see what flexibility he wants to clarify in implementations. 15:10:43 Cyril: I also have an update. 15:10:53 .. I talked to Glenn! He told me he wanted to write a PR. 15:11:01 .. I had the action, though I'm late doing it. 15:11:18 .. The agreement we had was that I would clarify the origin and axis in the case of tblr and we said we could leave 15:11:26 .. it undefined for other writing modes. That's my recollection. 15:11:40 .. Glenn told me he verified his TTPE implementation and is satisfied with it. 15:11:49 .. My understanding is he wanted to clarify the spec based on that implementation. 15:12:09 .. My original comment was about the lack of clear definition of the origin of the transform or the orientation of the axes, 15:12:16 .. and if any scaling or transformation needs to be done. 15:12:24 .. He told me he wants to clarify the same things. 15:12:42 .. It might go beyond what I thought we would do, but that was because of a lack of agreement 15:12:48 .. on what to do for the other writing modes. 15:13:05 .. If we have a proposal we can decide if we want to adopt it (for the other writing modes) 15:13:43 Nigel: Thanks, anyone else want to raise anything on this issue now? 15:13:56 Atsushi: Nothing from me 15:14:37 SUMMARY: Waiting on Glenn @skynavga for a pull request to review 15:15:04 Topic: Mention fingerprinting vectors in privacy considerations. w3c/ttml2#1189 15:15:11 Nigel: This has been merged, there's nothing more to do here. 15:15:58 Topic: Clarify if the first ISD must/may be constructed when empty w3c/ttml2#1232 15:16:08 github: https://github.com/w3c/ttml2/issues/1232 15:16:26 Nigel: This has had a pull request open for >2 weeks, and we do not have consensus to merge it. 15:17:42 .. In fact there are objections to merging the pull request, despite it saying what I thought had been agreed in the issue. 15:17:58 .. It seems that the best action here is to close the PR and the issue, marking as "not doing". 15:19:24 .. The motivation was to try to help other downstream groups. We agreed there is flexibility in TTML2. 15:19:44 Pierre: It could be worth text that says "it is always possible to create an ISD everywhere, it just might be an empty ISD" 15:20:05 .. It's a useful observation because then it removes some difficult to define concepts such as root temporal extent. 15:20:20 .. You just run a procedure and then you always get something. 15:20:26 .. That's one useful outcome from the thread. 15:20:37 .. It's particularly useful when you put a TTML document on a timelines, 15:20:49 .. where that timeline could start before the begin on a body element for instance and could 15:20:53 .. end after the end time on the body element. 15:21:00 s/timelines/timeline 15:21:30 Cyril: You mentioned MPEG. It would be good for MPEG to have the text you proposed but not strictly necessary. 15:21:44 .. As long as we all agree, then we're good. 15:21:50 .. I like the text you suggested. 15:22:02 .. The only unclear part is what Pierre mentioned about the root temporal extent. 15:22:10 .. The rest is uncontroversial. 15:22:17 .. What's missing is the definition of an empty document. 15:22:30 .. There's some convergence on the empty TTML document defined by EBU. 15:22:38 .. But there's no definition of an empty ISD, is there? 15:22:44 Nigel: No, I don't think so. 15:23:50 .. I get the sense that no change is required but some change is helpful. 15:23:58 .. Should we continue the discussion and working on the pull request? 15:24:13 Pierre: My issue with the current pull request is that it suggests that there is a correct ISD sequence. 15:24:33 .. I think everyone can agree that there for T between 0 and infinity there is always an ISD. 15:24:51 Cyril: The wording proposed by Nigel is good, that defers to application. 15:25:00 .. I think the mention of root temporal extent was the problem for Glenn. 15:25:04 Pierre: That's my objection too. 15:25:09 Cyril: Maybe if we just remove that part. 15:25:36 Pierre: You can just say that for all time there is an ISD, rather than depending on an unclear begin and end, which don't matter. 15:26:47 Nigel: Trying to understand, so you want to say that a sequence of ISDs can be created from any TTML document such that 15:27:04 .. there is always an ISD for every positive time T, but that not all applications need to make that whole sequence. 15:27:52 Pierre: But the spec should not say "the ISD before some start time is undefined" : it's just empty. 15:28:15 Cyril: It's worth giving this a shot, understanding the objections better, now that we understand the objections from Pierre better. 15:28:27 Nigel: Okay, thank you, I'll continue to put effort into this. 15:28:46 SUMMARY: Nigel @nigelmegitt to attempt to resolve objections to the current PR text. 15:29:27 Topic: NBG(R_i) counts transparent backgrounds w3c/imsc#570 15:29:41 github: https://github.com/w3c/imsc/issues/570 15:30:22 Pierre: The issue here is the algorithm makes a difference if the background is not specified or is transparent, 15:30:28 .. but those two are really equivalent. 15:31:00 .. It doesn't make sense for two documents to result in different complexity just based on initial value or specified value, where they're the same. 15:31:59 Nigel: This is about the computed value rather than the specified value, because initial can change the default? 15:32:14 Pierre: Right, but right now the HRM is defined in terms of specified values if I'm not mistaken. 15:32:23 Nigel: That's weird! 15:32:40 Pierre: That was before initial, where for things that are not inherited it makes a difference. 15:32:48 .. That may be a separate issue that we need to fix. 15:32:54 Nigel: The two things go together. 15:33:16 Pierre: Sure, but even if initial is transparent, there should be no difference in complexity if one document specifies backgroundColor="transparent" 15:33:20 .. and the other one doesn't. 15:34:00 Nigel: If you change this to be based on computed values and change the algorithm to ignore transparent background values, that 15:34:03 .. would solve both issues? 15:34:11 Pierre: I agree, we could solve both at once that way. 15:35:16 Nigel: I think that makes the case for a change here more concrete. 15:35:35 .. My discussion comments before were based on reluctance to change HRM because it will create 15:35:47 .. new values, with new thresholds etc. so it could be costly for implementations. 15:35:56 Pierre: These three issues I filed were as a result of trying to implement the spec. 15:36:04 .. I'm not aware of any other implementation of the HRM. 15:36:14 .. Of course I was running my HRM code against sample documents. 15:37:19 Nigel: Any other questions or comments? 15:37:29 Pierre: I'll generate a pull request based on this. 15:37:46 SUMMARY: Pierre @palemieux to open a pull request as per the above discussion. 15:38:09 Topic: span elements are included in NBG(R_i) w3c/imsc#571 15:38:16 github: https://github.com/w3c/imsc/issues/571 15:38:38 Nigel: This is about where you count the background colour of spans. 15:38:51 Pierre: The problem with the current spec is that the cost of drawing a background on span 15:38:59 .. is the same as the cost of drawing a background on the entire region. 15:39:05 .. That seems to scale the wrong way. 15:39:21 .. Intuitively you'd think that the cost of drawing the background of a span 15:39:32 .. should roughly scale with the number of characters in the span, not the area of the region. 15:40:44 Nigel: My feeling is "kinda" and "maybe" and "it's not that bad is it?" 15:41:00 .. I mean, some spans might be as big as a region, but it's unusual. 15:41:20 .. As a worst case scenario, it's not so bad. We're just looking for a complexity value. 15:41:45 Pierre: It is bad though because a p with one span, compared to the same p with the same text in multiple spans, 15:42:04 .. generates a higher complexity value. 15:42:16 Nigel: You mean there are documents that fail compared to the threshold now, that should pass? 15:42:28 Pierre: Yes, there are cases where there are 2 documents with the same rendered output, 15:42:38 .. and one fails and one passes, based on how many spans are in the p output. 15:43:04 Nigel: It'd be good to see test cases. 15:43:20 .. Although the rendered output is the same, that doesn't mean that the rendering complexity was the same. 15:43:33 Pierre: Imagine an implementation that uses fixed width bitmap characters. 15:43:44 .. The cost of applying a background to a span should never scale as the area of the region, 15:43:55 .. because the background would scale with every character drawn. 15:44:14 .. You would not redraw the entire background of the region every time you blit a character. 15:44:30 .. it would just be the area of the character. 15:45:19 Nigel: It would be useful to have test cases. Am I right that there are no HRM tests in imsc-tests? 15:45:28 Pierre: Right, so the project I'm doing could probably add them. 15:45:53 Nigel: Any other thoughts on this? 15:46:12 SUMMARY: Continue the discussion on the issue 15:46:42 Topic: Add test for fillLineGap when background is semi-transparent w3c/imsc-tests#99 15:47:05 github: https://github.com/w3c/imsc-tests/issues/99 15:47:14 Nigel: Just to alert people to this, and mention the motivation. 15:48:56 .. I was experimenting with varying the opacity of tts:backgroundColor on span and found that when fillLineGap is enabled, 15:49:24 .. there's a high visual sensitivity to exact boundaries of spans, but no test cases, so I opened the pull request for this issue to add one. 15:49:31 .. May also be somewhat relevant for linePadding. 15:49:40 .. Please take a look. 15:50:02 SUMMARY: Group asked to review pull request 15:50:20 Topic: TPAC 2021 15:51:58 Nigel: I keep raising this because we need to make a decision, by 10 September, but we should try to do it sooner. 15:52:21 .. The list of topics we have is at w3c/ttwg#191, which has one entry on it now. 15:52:36 Atsushi: We can meet as a group any time, joint meetings might be helpful at TPAC. 15:52:45 Pierre: And it may be more convenient outside TPAC 15:52:49 Atsushi: Strong +1 15:52:54 Nigel: +1 from me too. 15:53:24 .. Is the thing we have to do by 10 September for both joint and group meetings? 15:53:44 Atsushi: 2 weeks are allocated for TPAC, one week for joint meetings, and the other for groups. 15:53:59 .. In that week we can propose joint meetings. 15:54:33 .. Not sure if that answers your question? 15:54:43 Nigel: I was thinking about the Chair's admin task to register by 10 Sep 15:54:49 Atsushi: Could we do what we did last time? 15:55:14 Nigel: Yes, would you like to take that on? 15:55:22 Atsushi: I can try to coordinate with the Chairs 15:55:28 Nigel: Sounds good to me, sort me and Gary out. Gary? 15:55:31 Gary: Sounds good 15:56:09 Pierre: It just occurred to me having this discussion about HRM, it would be awesome if for instance HbbTV, which I assume has 15:56:15 .. a lot of actual content, were to try the HRM. 15:56:24 i/P/Topic: AOB: IMSC HRM 15:56:42 .. There is actual a web app at hrm.sandflow.com and you can give it an ISOBMFF track file. 15:58:44 Cyril: Did I understand that the tool does not just single files but also multiple files? 15:59:10 Pierre: Thanks a lot for mp4box.js - you can give the tool a single document, a sequence of documents with a manifest json file, or an ISOBMFF file. 15:59:27 Cyril: I'll study it, because we only recently tried to define the behaviour of HRM for multiple documents in an MP4 file. 15:59:40 .. It would be interesting to see if you implemented it the same as MPEG specified it or not. 15:59:56 Pierre: Is there someone I could reach at HbbTV before this is made public and run some tests through it. 16:00:43 Nigel: Let me put you in touch with someone offline. 16:01:02 Pierre: Super, thanks. And Cyril, happy to discuss the processing of ISOBMFF track files. 16:01:18 Cyril: Sure, and I'm happy to run Netflix documents through too. 16:01:25 Nigel: I'd be interested to run BBC files through as well. 16:01:36 Pierre: I already found some bugs, so let's kick the tyres/ 16:01:58 Cyril: One question I had is: the HRM is about a single document, but in practice the problem is the peak. 16:02:04 .. Do you do any indication of the peak? 16:02:18 Pierre: Right now it reports every time the HRM is exceeded, and provides the temporal offset. 16:02:28 Cyril: I'd be interested in the raw numbers across the whole file. 16:02:35 Pierre: If you set logging to debug then it does that. 16:02:50 Cyril: I could try to correlate that with statistics on sessions where subs are missed. 16:03:13 Pierre: I'm not sure if the web app does but the command line does allow you to get the complexity of every single ISD. 16:03:23 Cyril: Excellent, looking forward to testing that, thank you. 16:04:22 Nigel: I wonder if it would be worth arranging some kind of session where we can discuss the HRM values for our content, 16:04:34 .. particularly if we change the HRM, so we can revalidate the threshold values. 16:04:45 Cyril: Doesn't have to be a session, can be offline. 16:04:58 .. I wouldn't invalidate Netflix content if it is fine in the field but fails the HRM 16:05:05 Pierre: Which is precisely why we should try it. 16:05:30 Topic: Meeting close 16:05:40 Nigel: We're 5 minutes over, let's adjourn. Thank you everyone. [adjourns meeting] 16:05:43 rrsagent, make minutes 16:05:43 I have made the request to generate https://www.w3.org/2021/06/10-tt-minutes.html nigel 16:09:11 Chair: Nigel, Gary 16:10:48 s/that there for T between/that for every T between 16:13:27 i/Atsushi: We can meet /Pierre: We could decide not to meet at TPAC 16:13:42 i/Atsushi: We can meet /Nigel: Yes, that's a valid decision for us to make. 16:14:27 rrsagent, make minutes 16:14:27 I have made the request to generate https://www.w3.org/2021/06/10-tt-minutes.html nigel 16:15:36 rrsagent, make minutes 16:15:36 I have made the request to generate https://www.w3.org/2021/06/10-tt-minutes.html nigel 16:18:52 scribeOptions: -final -noEmbedDiagnostics 16:18:58 zakim, end meeting 16:18:58 As of this point the attendees have been Nigel, Cyril, Pierre, Gary, Atsushi 16:19:00 RRSAgent, please draft minutes v2 16:19:00 I have made the request to generate https://www.w3.org/2021/06/10-tt-minutes.html Zakim 16:19:03 I am happy to have been of service, nigel; please remember to excuse RRSAgent. Goodbye 16:19:07 Zakim has left #tt 16:23:06 rrsagent, excuse us 16:23:06 I see no action items