IRC log of tt on 2021-04-29

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