IRC log of tt on 2022-10-13

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Meeting: Timed Text Working Group Teleconference
15:02:45 [nigel]
Present: Andreas, Hew, Nigel
15:02:48 [nigel]
scribe: nigel
15:02:52 [nigel]
Chair: Nigel
15:02:55 [nigel]
Regrets: Gary
15:03:06 [nigel]
Agenda: https://github.com/w3c/ttwg/issues/229
15:03:34 [nigel]
Previous meeting: https://www.w3.org/2022/10/06-tt-minutes.html
15:04:25 [Hew]
Reminder that the meeting is on Zoom today...
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Present+ Pierre
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Present+ Atsushi
15:07:01 [nigel]
Topic: This meeting
15:07:24 [nigel]
Nigel: Today we have DAPT issues, IMSC-HRM (one pull request/issue)
15:07:34 [nigel]
.. and any update on the charter FO.
15:07:45 [nigel]
.. Is there any other business, or anything to make sure we cover?
15:08:16 [nigel]
Hew: I can give some feedback on DAPT-REQs
15:08:28 [nigel]
Nigel: That'd be great, thank you
15:08:38 [nigel]
group: no other business
15:09:06 [nigel]
Topic: IMSC-HRM - Coalesce empty ISDs into non-empty ISDs w3c/imsc-hrm#50
15:09:07 [Github]
https://github.com/w3c/imsc-hrm/pull/50 : Coalesce empty ISDs into non-empty ISDs
15:09:18 [nigel]
github: https://github.com/w3c/imsc-hrm/pull/50
15:10:47 [nigel]
Nigel: This PR is primarily to deal with the clears and short gaps between ISDs - is that right?
15:11:03 [nigel]
Pierre: We're trying to address the industry practice of 2 frame gaps between successive
15:11:05 [nigel]
.. subtitles or captions.
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.. Today the HRM imposes a very high cost to those short gaps.
15:11:19 [nigel]
.. This PR addresses that.
15:11:46 [nigel]
.. I think we're down to just one question:
15:11:53 [nigel]
.. Should there be any cost to displaying an empty ISD?
15:12:02 [nigel]
.. i.e. painting it and presenting it
15:12:16 [nigel]
.. I am arguing that because the model assumes that subtitles are painted and presented on
15:12:31 [nigel]
.. a graphics plane that is then overlaid on to the related video object, then displaying nothing
15:12:40 [nigel]
.. costs nothing because you don't display that pane altogether.
15:12:44 [nigel]
Andreas: Makes sense to me.
15:12:55 [nigel]
Pierre: Another goal of this PR is to make as little change as possible.
15:13:11 [nigel]
.. That's where my mind is, why I'm arguing that there is no cost with presenting and painting empty ISDs.
15:13:20 [nigel]
q+
15:13:33 [nigel]
Andreas: As I understand there's no algorithm that would calculate a clearing action, right?
15:13:51 [nigel]
.. What it means to have an empty ISD that follows an ISD with content, that would then be a clearing action.
15:14:05 [nigel]
Pierre: My suggestion is that clearing happens only in the buffers where things are going to be painted.
15:14:16 [nigel]
.. Before drawing a new non-empty ISD you have to clear the back buffer, and that has a cost.
15:14:31 [nigel]
.. You first clear that, then draw the non-empty ISD, then when the presentation time comes in you
15:14:36 [nigel]
.. flip the buffer and display it.
15:14:54 [nigel]
.. If you clear it before then there's no cost because you just don't display the buffer.
15:15:15 [nigel]
.. Clearly the "clear" is related to the cost of clearing the buffer onto which an ISD is painted.
15:15:39 [nigel]
.. What I'm suggesting is that in fact there is no need to paint empty ISDs so there's no cost to not displaying
15:15:43 [nigel]
.. the graphics plane, period.
15:15:46 [nigel]
q?
15:16:14 [nigel]
Nigel: That's an argument I hadn't understood before, so good to know.
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ack n
15:16:31 [nigel]
Pierre: By the way I'm just trying to come up with something that requires as little change as possible
15:16:44 [nigel]
.. to the model. I hadn't thought exactly this 2 weeks ago for instance.
15:17:15 [nigel]
Nigel: Good to clarify that you're not saying that the cost of CLEAR is zero.
15:17:28 [nigel]
Pierre: Yes, the cost of CLEAR is not zero, but there's nothing to clear for empty ISD.
15:18:53 [nigel]
Nigel: Then the question is if we always need at least one buffer to be composited, and
15:19:05 [nigel]
.. therefore that we need to count the cost of clearing a buffer at least once for each clear.
15:19:14 [nigel]
.. Or can we just say "stop compositing" at no cost.
15:19:30 [nigel]
.. I think the conservative approach is to say that we assume there is always exactly one buffer
15:19:45 [nigel]
.. being composited, and therefore we need to count the cost of preparing an empty buffer if there is
15:19:53 [nigel]
.. to be an empty ISD after the current one.
15:20:12 [atai]
q+
15:20:24 [nigel]
Pierre: Within the model that's not possible with only 2 buffers.
15:20:45 [nigel]
.. If you clear the back buffer for the empty ISD and then present it then you have to wait
15:20:59 [nigel]
.. for the empty ISD to be presented which defeats the purpose. You would need a third buffer.
15:21:14 [nigel]
.. What I have in mind is that the screen is being refreshed by the video.
15:21:26 [nigel]
.. There's no cost to not painting on the next refresh. Not drawing an overlay is a no-op.
15:21:55 [nigel]
.. When the next frame comes in you draw neither of the two buffers.
15:21:57 [nigel]
ack a
15:22:10 [nigel]
Andreas: The HRM is a theoretical construct to calculate presentation cost of ISDs.
15:22:21 [nigel]
.. That doesn't mean that is how it is implemented in practice.
15:22:37 [nigel]
.. You could view it like you do but of course in practice it could be like Nigel says when empty ISDs come in.
15:22:49 [nigel]
.. Follow a logic that is not yet implemented in the HRM.
15:22:55 [nigel]
Pierre: Sure, exactly, I agree.
15:23:06 [nigel]
.. I think what we're trying to do here is to tease out where the main complexity is, how it scales.
15:23:24 [nigel]
.. I think I'm arguing, I've convinced myself, in general, you could have a cost to not displaying pixels,
15:23:40 [nigel]
.. you could have a third buffer, maybe your implementation is on still images and clearing has a cost,
15:23:55 [nigel]
.. but in the case of video the cost of not displaying an ISD is not substantial and can therefore be safely
15:23:56 [nigel]
.. ignored.
15:24:59 [nigel]
Nigel: Sudden moment of clarity for me that the current pre-PR HRM is what you have to end up with
15:25:03 [nigel]
.. if you have a 2 buffer model.
15:26:39 [nigel]
.. I think what we're discussing here is that the idea is the implementation flips from compositing
15:26:44 [nigel]
.. buffer A to B to A to B etc
15:26:55 [nigel]
.. but in my mind I'd imagined that there was a compositing plane C
15:27:14 [nigel]
.. and the task is to blit A to C, B to C, A to C etc which would have a very different set of constraints.
15:27:18 [nigel]
.. I'm not sure which it is right now.
15:27:32 [nigel]
Pierre: The presentation buffer Pn-1 is directly connected to the display in figure 2.
15:28:24 [nigel]
.. This was designed with a simple TV architecture in mind, where one or the other is displayed on screen,
15:28:31 [nigel]
.. or read directly by the display circuitry.
15:29:14 [nigel]
Nigel: I see what you mean about fig 2.
15:29:51 [nigel]
.. But again, fig 2 has no switch about whether the presentation buffers are connected to the display or not.
15:30:02 [nigel]
Pierre: We could add that to the model, that with empty ISDs nothing is displayed.
15:30:40 [nigel]
.. The PR has text that goes beneath that figure, but we could modify the figure to make it clearer.
15:32:11 [nigel]
Nigel: Yes. I'm just wondering which is preferable, to insert a switch to the display
15:32:21 [nigel]
.. or to posit a 3rd buffer.
15:32:31 [nigel]
Andreas: A new buffer would add more complexity to the model, right?
15:32:38 [nigel]
Nigel: I don't really think so.
15:32:55 [nigel]
Andreas: For me the question is if for some implementations there would be some cost when an
15:33:07 [nigel]
.. empty ISD is going through the change, and if this cost is high enough to be taken into account
15:33:13 [nigel]
.. for the calculation of complexity.
15:33:16 [nigel]
Pierre: Exactly.
15:33:27 [nigel]
Andreas: The cost is negligible and not go into the calculation.
15:34:35 [nigel]
Nigel: I don't think that introducing the third buffer and counting the cost of a CLEAR would not
15:35:16 [nigel]
.. fail anything that passes today, but there are some documents that could potentially fail it,
15:35:20 [nigel]
.. and we should catch those.
15:35:31 [nigel]
Pierre: Concerned about the editing complexity that would introduce.
15:35:48 [nigel]
Nigel: I haven't done the exercise, it seems like it _should_ be simple, but maybe not.
15:36:01 [nigel]
Pierre: If you want to try making the edit, go ahead. I'm not sure what it will look like.
15:36:11 [nigel]
.. You need to introduce the cost of drawing into the back buffer.
15:36:31 [nigel]
Nigel: I would have to make the assumption of a cost-free blit into the third, composition buffer.
15:36:47 [nigel]
Pierre: If you want to give it a shot, as we pointed out, adding the cost of a clear for an empty ISD
15:36:59 [nigel]
.. will land up with results that are closer to what we have today. It's not going to
15:37:09 [nigel]
.. invalidate documents that are valid today. That's not my concern.
15:37:17 [atai]
q+
15:37:22 [nigel]
.. It's updating the text in a way that does not cause more trouble than it solves.
15:37:36 [nigel]
.. I'm happy to modify figures - I have the master files, though they may be checked in.
15:37:38 [nigel]
ack at
15:37:52 [nigel]
Andreas: I want to echo a bit Pierre's concern more about the complexity of the specification and
15:37:59 [nigel]
.. unexpected consequences of adding a new concept.
15:38:12 [nigel]
.. The issue is that the whole model is already not so easy to get, from non experts
15:38:17 [nigel]
.. or people who really need to implement it.
15:38:25 [nigel]
.. Adding a new component just increases the complexity of the model.
15:38:31 [nigel]
.. From an understanding point of view.
15:38:44 [nigel]
.. When we consider adding it, we should compare the benefit of adding it to the
15:39:01 [nigel]
.. benefit we get from getting closer to reality for this particular case.
15:39:13 [nigel]
.. We heard that even if we add a component it would not really change the results very much.
15:40:00 [nigel]
Nigel: Either proposal is a change to the model.
15:40:05 [nigel]
.. I'm concerned about clarity of that change.
15:40:14 [nigel]
.. The risk is that it's so subtle that it is not actually noticed properly.
15:41:30 [nigel]
.. I'm not sure if the mathematical results would be identical.
15:41:41 [nigel]
Pierre: They would not be because you'd count one extra CLEAR per sequence of ISDs.
15:41:53 [nigel]
.. Neither proposal would invalidate a set of valid documents, which they don't want to do.
15:42:03 [nigel]
s/they don't/we don't
15:42:49 [nigel]
Nigel: I'm interested to know what is the edge case between the two ideas where
15:43:00 [nigel]
.. one would validate a document and the other would say it is invalid.
15:43:26 [nigel]
Pierre: The cost of that extra clear would be included in the cost of painting the following non-empty ISD, right?
15:43:29 [nigel]
Nigel: I think so.
15:43:33 [nigel]
Pierre: Let me try something.
15:43:43 [nigel]
.. Scenario: non-empty ISD, empty ISD, non-empty ISD
15:44:08 [nigel]
.. The model limits the complexity by saying painting the second non-empty ISD takes some time
15:44:18 [nigel]
.. and the system has some time to do that, and what we're saying now is that the
15:44:32 [nigel]
.. time available to paint the second non-empty ISD is the time between the presentation time of
15:44:56 [nigel]
.. difficult to say without graphics on screen - [shares screen]
15:50:54 [nigel]
.. [discussion of 2 buffer model plus 3 buffer model by looking and pointing at the rendering time figure]
15:51:14 [nigel]
Pierre: We could schedule some time for a call next week?
15:51:32 [nigel]
Nigel: That's a good shout - I should be able to do that.
15:51:43 [nigel]
Pierre: I'd really like to get to the point where we ask for feedback, and
15:51:52 [nigel]
.. we need to complete this issue before we do so.
15:51:56 [nigel]
Nigel: Yes
15:52:20 [nigel]
Pierre: I am available at the same time next week
15:52:25 [nigel]
Nigel: Me too
15:52:41 [nigel]
SUMMARY: Discussions to continue offline and possibly in additional call
15:54:05 [nigel]
Topic: DAPT-REQs
15:54:36 [nigel]
Hew: Our AD operations and product owner reviewed DAPT-REQs and felt
15:54:47 [nigel]
.. that it captured their current workflows and that there would be no problem
15:54:52 [nigel]
.. capturing what they do, within it.
15:55:02 [nigel]
.. They raised possible future questions.
15:55:21 [nigel]
.. For example richer pan options if you want to get creative in e.g. 5.1 audio or other distribution approaches.
15:55:37 [nigel]
.. They wondered about extensible synth voice options to include tone.
15:55:44 [nigel]
Nigel: Emotional tone maybe? Pitch is already available.
15:55:58 [nigel]
Hew: Yes, that could well be what they meant.
15:56:12 [nigel]
.. If you think about dramatic AD particularly they try to carry the tension or emotion of the programmes.
15:56:15 [nigel]
s/s//
15:56:27 [nigel]
Hew: That was it.
15:56:39 [nigel]
Nigel: Great, thank you, always very helpful to get reviews.
15:56:49 [nigel]
Topic: Charter FO Status update.
15:57:09 [nigel]
Nigel: As discussed last week I submitted the Chair's report, and I got an acknowledgement back.
15:57:20 [nigel]
.. I expect the Chair's report to be appended to the document.
15:57:26 [nigel]
.. Atushi, anything to add?
15:57:32 [nigel]
s/Atushi/Atsushi
15:57:51 [nigel]
Atsushi: The report will be made available to the FO Council in the next couple of days.
15:58:16 [nigel]
.. Stepping down from Council is ongoing - I am not sure when they will actually start to discuss it.
15:58:33 [nigel]
.. I believe they have 2.5 weeks for stepping down prior to Team report so they should start shortly.
15:58:51 [nigel]
Nigel: Thanks for the update. Any questions?
15:59:03 [nigel]
.. I see nobody on the queue.
15:59:23 [nigel]
.. Q from me: did the Objectors respond to the draft Team report?
15:59:39 [nigel]
Atsushi: I have not seen a response. WG participants can see the updated report at the same URL.
15:59:45 [nigel]
Nigel: Thank you.
15:59:56 [nigel]
Topic: Meeting close
16:00:19 [nigel]
Nigel: Thanks everyone! [adjourns meeting]
16:00:31 [nigel]
rrsagent, make minutes
16:00:31 [RRSAgent]
I have made the request to generate https://www.w3.org/2022/10/13-tt-minutes.html nigel
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s/tenion or emotion of the programmes/tension or emotion of the programme
16:13:09 [nigel]
s/I don't think that introducing the third buffer/I think that introducing the third buffer
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rrsagent, make minutes
16:15:43 [RRSAgent]
I have made the request to generate https://www.w3.org/2022/10/13-tt-minutes.html nigel
16:16:24 [nigel]
scribeOptions: -final -noEmbedDiagnostics
16:16:27 [nigel]
zakim, end meeting
16:16:27 [Zakim]
As of this point the attendees have been Andreas, Hew, Nigel, Pierre, Atsushi
16:16:29 [Zakim]
RRSAgent, please draft minutes v2
16:16:29 [RRSAgent]
I have made the request to generate https://www.w3.org/2022/10/13-tt-minutes.html Zakim
16:16:32 [Zakim]
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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rrsagent, excuse us
16:40:04 [RRSAgent]
I see no action items