15:00:44 RRSAgent has joined #tt 15:00:44 logging to https://www.w3.org/2021/04/29-tt-irc 15:00:46 RRSAgent, make logs Public 15:00:48 Meeting: Timed Text Working Group Teleconference 15:02:33 present+ Chris_Needham 15:03:03 Agenda: https://github.com/w3c/ttwg/issues/184 15:03:07 scribe: nigel 15:03:38 present+ Rob_Smith 15:04:09 Present+ Glenn, Pierre, Rob_Smith, Nigel 15:04:14 Chair: Nigel, Gary 15:04:33 Previous meeting: https://www.w3.org/2021/04/01-tt-minutes.html 15:04:42 Topic: This meeting 15:05:25 present+ 15:05:34 Nigel: Today, we have 2 points on TTML2 and I'd like to take a minute to cover https://github.com/w3c/ttml2/issues/1189 15:05:58 cyril has joined #tt 15:06:08 Present+ Atsushi, Cyril 15:06:43 .. We also have a WebVTT pull request to check on, for unbounded cue end times. 15:06:49 .. In AOB we currently have TPAC 2021. 15:07:21 Cyril: I can give an update on TTML and WebVTT discussions in MPEG if we have time in AOB 15:07:30 Nigel: Thank you. Any other business? 15:08:03 group: [no other business] 15:08:15 Nigel: Since Gary is a few minutes late today I propose we cover the TTML2 issues first. 15:08:20 Chris: That's ok 15:08:23 Rob: Good for me. 15:09:23 Nigel: Welcome, it's a W3C WG meeting, usual rules apply, we're nice to each other, etc. almost goes without saying. 15:09:54 Topic: TTML2 - Merging open pull requests 15:10:10 Nigel: We have two open pull requests that have been open for more than 2 weeks and have an approval review. 15:10:24 .. By our normal rules, that constitutes consensus. 15:10:31 Glenn: Are these the 2 on TTML2? 15:10:33 Nigel: Yes 15:10:46 Glenn: I've just merged the first and will have merged the second in a minute or two. 15:10:48 Nigel: Great. 15:11:18 Glenn: I'd also point out that the first of those, to change the links examples to https is technically not necessary because they're not links. 15:12:07 Nigel: The point was to demonstrate editorially that we want to promote use of secure protocols. 15:12:11 Glenn: Yes. 15:12:37 Topic: TTML2 - Shear calculations and origin of coordinate system. w3c/ttml2#1199 15:12:53 github: https://github.com/w3c/ttml2/issues/1199 15:13:32 present+ Gary 15:13:35 Nigel: Following my proposal about line wrapping and block shear, Glenn you wanted to add something? 15:13:56 Glenn: In TTPE we implemented this in a branch. We computed the line measure for the block prior to performing 15:14:13 .. paragraph line breaking operations. We computed that measure based on the block shear that would apply to the block, so it has the 15:14:27 .. result of resulting the measure by some %age related to the sines or cosines of the angle. 15:14:42 .. It did not require any kind of recursive update to the measure for formatting purposes. 15:14:59 .. Once you've computed the line measure then it's done and you don't need to recompute. 15:15:12 .. I will go back to your issue and see if you're thinking of something I had not considered. 15:15:22 .. We didn't have any problem of the sort that you mentioned. 15:15:37 Nigel: I'm confused by that so will await your further input. 15:16:19 SUMMARY: @skynavga to consider computational issue further 15:16:36 Topic: Mention fingerprinting vectors in privacy considerations. w3c/ttml2#1189 15:16:43 github: https://github.com/w3c/ttml2/issues/1189 15:17:09 scribe+ cpn 15:17:26 Nigel: I've reviewed the fingerprinting vectors just before today's meeting 15:17:46 ... I came up with 3 actions, all to add notes to the Privacy section 15:18:42 ... [describes the actions in https://github.com/w3c/ttml2/issues/1189#issuecomment-829305696] 15:20:08 Glenn: Do any of those involve change to the font fingerprinting text? 15:20:24 Nigel: No, they're just adding points to P7 and P3. It doesn't modify P10 15:20:56 Nigel: I'm happy to draft a PR, unless someone else wants to 15:21:04 scribe: nigel 15:21:30 SUMMARY: @nigelmegitt listed the proposed changes and highlighted them to the group for consideration 15:21:56 Topic: WebVTT Add unbounded TextTrackCue.endTime w3c/webvtt#493 15:22:11 github: https://github.com/w3c/webvtt/pull/493 15:23:04 Gary: When we last spoke about the unbounded end time for the TextTrackCue there wasn't much concern. 15:23:17 .. The hold-up was whether there were tests and whether it was approved on the HTML spec side. 15:23:39 .. Last week the [PRs on] tests and the HTML side were merged so now WebVTT is the last hold-out for the API change, 15:23:43 .. which is this pull request right now. 15:23:43 q+ 15:23:55 ack R 15:24:16 Rob: I concur. Firstly this is my first TTWG meeting, thank you for the invite. Thanks Gary for the quick summary. 15:24:31 .. I'd add that having done the platform tests I notice there's a dependency between the TextTrackCue tests and the VTTCue tests 15:24:50 .. because the TextTrackCue relies on VTTCue for the constructor. There's a crossover or interdependency that results. 15:25:04 .. The WebVTT change is required to make the Web Platform Tests work as well. 15:25:11 Gary: Thanks Rob that makes sense. 15:25:56 .. In terms of process, I haven't heard any objections from anyone. Do we need to wait before merging for the resolution period? 15:26:20 Nigel: Our normal practice is to consider the opening of a PR as effectively a Call for Consensus 15:26:40 .. so that the Decision Review period expires 2 weeks after opening, obviously assuming there is consensus at that time. 15:27:17 .. What this means is that, since this PR has been open since November, if the Chair declares consensus, then the Editor can go ahead and merge. 15:27:29 q+ 15:27:44 .. I'd just point out that there was a commit just 23 hours ago so that should be considered. 15:27:56 Gary: I plan to look through it again after this meeting and in that case go ahead and merge. 15:27:59 ack R 15:28:02 q+ to ask about the VTT format discussion 15:28:25 Rob: That recent addition was to address Philip Jaegenstadt's comment that there was a reference to unbounded TextTrackCue which was 15:28:48 .. not used. We tried to keep it as simple as possible and ended up removing all references to unbounded cues in the process. 15:29:03 .. The way it is at the moment it is the one thing we are adding and do not mention, so I thought it worth adding. 15:29:10 s/Jaegenstadt/Jaegenstedt/ 15:29:22 .. I couldn't find any similar example and struggled with the wording so would welcome guidance. 15:29:36 Gary: Earlier I thought it was fine but will take a closer look. 15:29:38 Rob: Thank you 15:29:54 q++ nigel 15:30:56 ack n 15:31:24 ack + 15:31:51 Gary: Then for the pull request the resolution is for me to look over it and merge after approval. 15:31:52 q+ 15:32:14 q- cpn 15:32:21 ack Rob 15:32:38 Rob: Gary, if there's change to be made on the wording I'm happy to work with you to get that resolved and complete this. 15:32:40 Gary: Thank you Rob 15:33:10 RESOLUTION: Gary to do final Editorial pass and merge 15:35:38 Topic: TPAC 2021 15:35:53 Nigel: TPAC dates have been circulated; TPAC will be virtual, and be held from 18-29 October. 15:36:03 .. The week from 25 to 29 October will be dedicated to the Joint and Group meetings. 15:36:21 .. The question for us is: Do we wish to meet? 15:36:30 .. We have until 10 September to declare meeting dates. 15:37:30 .. I think we do have some agenda points for joint meetings or a group meeting that we wanted to cover over the past couple of years 15:37:35 .. but never got around to. 15:37:48 Gary: Last year we wanted to meet with CSS WG but forgot to confirm that. 15:37:49 Nigel: Yes. 15:38:00 .. On a personal level, the timing is terrible for me this year! 15:38:42 .. We have some time, but I wanted to give plenty of notice. 15:38:55 .. If anyone does have any agenda topics for a meeting in October, do let me and Gary know. 15:39:17 Topic: AOB: TTML and WebVTT at MPEG 15:39:21 Cyril: A quick update. 15:39:38 .. As you know, MPEG is working on an amendment to 14496-30. The initial purpose of the amendment 15:39:58 .. was to clarify terminology around TTML. Specifically it is not always clear how to package TTML in an MP4 track, 15:40:11 .. if the document is longer than the sample in which it is contained, for example. 15:40:25 .. So the clarifications are those we discussed some time ago. 15:40:38 .. It is progressing well. The changes since last time are additions of more examples. 15:40:47 .. You should have access to the documents but if not then I will share with you. 15:41:07 .. We're adding more examples where we detail first typical use cases, how the ISDs are created and then how they are 15:41:24 .. packaged into MP4 samples and presented. What we've clarified in the latest round is, with respect to IMSC 1.1 and its HRM, 15:41:43 .. the HRM in IMSC indicates how it works on a document, so you take the sequence of ISDs and apply the HRM on that sequence. 15:42:01 .. We're proposing to extend the HRM to all the ISDs produced by the entire track of documents, as an extension. 15:42:21 .. We're recommending behaviour when the last ISD of a sample is the same as the first ISD of the next sample, avoiding flickering for example. 15:42:27 .. That's it for TTML for example. 15:43:04 Nigel: I'd like more information on how to access the document, if you're able to help with that, bearing in mind the liaison we have. 15:43:13 Cyril: I will work offline on that, alongside Mike Dolan. 15:43:55 Nigel: Was there any consideration about how to apply edit lists? 15:44:14 Cyril: Nigel, your colleague Stephen supplied some comments and he was right. We're working on changes for that. 15:44:37 .. For all the operations on clipping, imagining the TTML document needs clipping to the time interval of a sample, the question is what 15:44:56 .. timeline do you use. The agreement was that it is the composition time before the edit list is applied. Then the edit list puts that on the timeline. 15:45:21 .. Concrete example. TTML document 0s - 10s. Sample interval 2s - 5s. 15:45:28 .. That's the sample's composition time interval. 15:45:34 .. So you display only part of the document. 15:45:43 .. Then the edit list shifts this sample to 0s. 15:46:05 .. The first thing that will be presented in this case is the content of the document from 2s - 5s which is presented beginning at time 0s. 15:46:28 .. We think this is applicable to WebVTT as well, the same clarification to use composition time instead of presentation time. 15:46:33 Nigel: That's really good, thank you. 15:47:05 Cyril: Moving on to WebVTT. There was a contribution and the document proposed changes to the carriage of WebVTT to cover 15:47:09 .. the carriage of indefinite cues. 15:47:26 .. There are two aspects. Firstly the draft was not completely clear and more improvements will be needed. 15:47:41 .. In particular we have two tools to indicate an indefinite cue. 15:47:56 .. 1. Sample duration = 0 means "indefinite cue" but it is only allowed as the last sample in the track. 15:48:18 .. When you're producing live WebVTT and packaging it you won't know when the last sample will be so you cannot use it, or you use it 15:48:32 .. all the time and have plenty of samples with duration zero which is not allowed in the spec. 15:48:55 .. 2. The sample has a definite duration, e.g. valid for at least 2s, so you put that as the duration and after that you extend the duration 15:49:14 .. of the sample by marking it as redundant and having a duration that is 2 additional seconds, and you keep sending that until something 15:49:19 .. changes, or the end of the presentation. 15:49:36 .. There is no strong recommendation yet to use that. The discussion is ongoing. 15:49:52 .. It is all based on the assumption that there is a way in WebVTT to identify an indefinite cue. 15:50:07 q+ 15:50:15 .. To my knowledge there is no syntax yet to indicate indefinite cue duration, and it's a hard problem if you consider backwards compatibility. 15:50:19 Nigel: Right! 15:50:22 ack R 15:50:36 Rob: Can I ask what is the definition of an indefinite cue? 15:50:52 Cyril: Good question. How is it defined in HTML and the WebVTT JS API? 15:51:00 Gary: It's another word for "unbounded" 15:51:10 Cyril: OK replace indefinite with unbounded. 15:51:28 Glenn: It's a term from SMIL and we use it in TTML to refer to a duration with no specific end. 15:51:30 Rob: Thank you. 15:51:52 .. So then I think w3c/webvtt#496 is relevant to this. 15:52:14 .. I'm an Invited Expert in [??? 15:52:37 ... and have been working on WebVMT based on WebVTT but designed to express location, 15:52:53 .. and has expanded to cover metadata. Particularly location-aware video devices with sensors on them. 15:53:12 .. The unbounded cue idea I proposed here was to address the live capture use case that I was considering for WebVMT. 15:53:35 .. There's been some work done proposing a syntax which could be ported back to WebVTT, because the text track cue structure 15:53:55 .. is shared between WebVTT and WebVMT. There have been discussions about recording sensor values and interpolating them between 15:54:15 .. time samples, and handling discontinuities, which all seem relevant, so it might be worth having a discussion about that at some stage. 15:54:18 q+ 15:54:38 .. I can post a link to last year's TPAC discussion which probably summarises this fairly well, and also feeds into issue 496 which I raised, 15:54:43 .. and welcome feedback on that. 15:54:43 -> https://github.com/w3c/webvtt/issues/496 unbounded webvtt cue syntax use cases and discussion 15:54:50 ack cp 15:54:59 Chris: My question follows from what Rob was just saying. 15:55:10 .. It seems that we have a number of different constituencies that are interested in this. 15:55:31 .. Rob with WebVMT, WebVTT with unbounded cues in MPEG4, and in the Media Timed Events IG, emsg boxes, 15:55:45 .. and those can have unbounded duration as well. In the last meeting that we had there, 15:55:57 .. Nigel suggested that we ought to do a use case and requirements gathering so that we understand what 15:56:06 .. problem we are trying to solve when we make syntax changes. 15:56:19 .. My question is where do we want the home for that discussion to be? 15:56:39 .. Following on from that I would like a clear definition of the precise questions. 15:56:54 .. My proposal is to take this on under the MEIG Timed Events activity 15:57:08 .. so what I've tentatively done is put it on the agenda for the next MEIG call which will be on 15:57:26 .. May 11, Tuesday, the purpose of which is to introduce the topic to MEIG more generally and 15:57:57 .. then use that to identify who needs to be involved in the discussion and point people towards that timed events activity. 15:58:06 .. I wanted to ask if you think that's a good approach. 15:58:06 q+ 15:59:34 Nigel: I think that's a good idea, yes. 15:59:35 q+ 15:59:46 ack n 16:00:03 Nigel: Regarding specific questions, there's backwards compatibility. MPEG4 has an approach where you can keep extending. That's similar to the TTML approach. At least one proposal out there relies on a particular error condition behaviour, so it's not clear what the backwards compatibility story is. Need to establish what's acceptable. 16:00:22 Gary: I agree with Nigel, I think discussing in MEIG is a great place. 16:00:41 .. For now, if anyone has specific comments, putting it in webvtt issue 496 would be good to keep things in one place until we decide 16:00:44 .. there's a better place. 16:00:53 q+ 16:01:11 .. I agree that backwards compat is important and we need to figure out what behaviour we want and if we also want forwards compatibility. 16:01:32 .. For example the current proposed syntax of not having end time is technically backwards compatible but old clients just won't see those 16:01:41 .. cues. They won't break but it is not necessarily good behaviour. 16:01:56 .. In addition, any syntax change is going to be hard because we need to guage implementer interest. 16:02:15 .. In recent years they have been very reluctant. If noone wants to implement then is there really any point in doing this? 16:02:21 s/guage/gauge 16:02:41 Chris: That's great, due to time I didn't want to go into too much tech detail. This is the conversation I hope we can have. 16:02:47 ack g 16:02:49 ack R 16:03:09 Rob: There are existing solutions to this using bounded cues as opposed to unbounded ones and they still work so if there is an 16:03:24 .. issue with backwards compatibility the user already has the choice to use those existing structures. 16:03:25 q? 16:04:05 Topic: Meeting close 16:04:32 Nigel: We're a few minutes over, and we've covered all the agenda and more today. So thank you everyone, we're adjourned for today. 16:04:36 .. [adjourns meeting] 16:04:41 rrsagent, make minutes v2 16:04:41 I have made the request to generate https://www.w3.org/2021/04/29-tt-minutes.html nigel 16:08:44 s/.. I'm an/Rob: I'm an 16:09:29 i/Rob: I'm an/Topic: WebVTT Unbounded Cue Use Cases w3c/webvtt#496 16:10:44 i/Topic: TTML2 - Shear calculations/Glenn: (later update) I've merged the second pull request also. 16:11:35 s/ack +// 16:14:22 i/Nigel: Regarding specific questions/scribe: cpn 16:14:35 i/Gary: I agree with Nigel/scribe: nigel 16:14:42 rrsagent, make minutes v2 16:14:42 I have made the request to generate https://www.w3.org/2021/04/29-tt-minutes.html nigel 16:15:01 (nigel, sorry that forgot to tell, v2 turns into the default for rrsagent from early this year - so no need v2 in cmd) 16:20:41 s|unbounded webvtt cue syntax use cases and discussion|unbounded webvtt cue syntax use cases and discussion w3c/webvtt#496 16:21:33 s/backwards compat is/backwards compatibility is 16:27:30 s/in [???/and Chair the Web Video Map Tracks (WebVMT) Community Group 16:27:49 rrsagent, make minutes v2 16:27:49 I have made the request to generate https://www.w3.org/2021/04/29-tt-minutes.html nigel 16:30:03 s/(nigel, sorry that forgot to tell, v2 turns into the default for rrsagent from early this year - so no need v2 in cmd)// 16:30:07 rrsagent, make minutes 16:30:07 I have made the request to generate https://www.w3.org/2021/04/29-tt-minutes.html nigel 16:30:54 mmm.. is this not that one? 16:31:08 Present- atsushi_ 16:31:38 rrsagent, make minutes 16:31:38 I have made the request to generate https://www.w3.org/2021/04/29-tt-minutes.html nigel 16:32:47 s/mmm.. is this not that one?// 16:33:26 rrsagent, make minutes 16:33:26 I have made the request to generate https://www.w3.org/2021/04/29-tt-minutes.html nigel 16:33:38 scribeOptions: -final -noEmbedDiagnostics 16:33:50 zakim, end meeting 16:33:50 As of this point the attendees have been Chris_Needham, Rob_Smith, Glenn, Pierre, Nigel, atsushi_, Cyril, Gary 16:33:52 RRSAgent, please draft minutes v2 16:33:52 I have made the request to generate https://www.w3.org/2021/04/29-tt-minutes.html Zakim 16:33:55 I am happy to have been of service, nigel; please remember to excuse RRSAgent. Goodbye 16:33:59 Zakim has left #tt 16:34:05 rrsagent, excuse us 16:34:05 I see no action items