15:01:08 RRSAgent has joined #tt 15:01:08 logging to https://www.w3.org/2022/10/27-tt-irc 15:01:11 RRSAgent, make logs Public 15:01:11 Meeting: Timed Text Working Group Teleconference 15:01:18 scribe: nigel 15:01:25 Chair: Nigel 15:01:27 Regrets: Gary 15:01:31 Present: Nigel 15:02:54 Present+ Pierre, Andreas 15:03:27 atai has joined #tt 15:08:18 Previous meeting: https://www.w3.org/2022/10/13-tt-minutes.html 15:09:00 Topic: This meeting 15:09:09 Agenda: https://github.com/w3c/ttwg/issues/230 15:09:36 Nigel: Without Cyril, not sure we should look at the DAPT issues. 15:09:42 Regrets+ Cyril 15:10:15 Nigel: So that leaves IMSC-HRM and any news on the Charter FO. 15:10:33 .. Any other business? 15:10:37 Andreas: Nothing from me 15:10:54 pal has joined #tt 15:10:55 Topic: Coalesce empty ISDs into non-empty ISDs w3c/imsc-hrm#50 15:10:56 https://github.com/w3c/imsc-hrm/pull/50 : Coalesce empty ISDs into non-empty ISDs 15:11:07 github: https://github.com/w3c/imsc-hrm/pull/50 15:11:25 Nigel: Pierre and I had a design chat about this last week 15:11:33 Present+ Atsushi 15:11:44 Pierre: Yes, I'd like to share my latest thoughts. I've spent a lot of time on this. 15:12:00 .. [shares screen] 15:12:43 .. [screen shows updated model with a switch between the presentation buffer and the display, to allow 15:12:50 .. clearing to happen by not compositing] 15:13:09 .. The path I'm going down as a proposal is that every ISD that comes in, decide if it is empty or not. 15:13:19 .. If it is not empty, go through the same process as the current HRM. 15:13:37 .. If it is an empty ISD, toggle the output of the current model, to turn off the output of the presentation buffer. 15:13:46 .. The idea is that an empty ISD is empty so there is nothing to display. 15:14:08 .. What it really means is that the cost of processing empty ISDs is zero because there is nothing to render. 15:14:22 .. Separately Nigel and I discussed whether or not there should be additional constraints on the 15:14:37 .. duration of empty ISDs, to catch errors seen in IMSC files where very small gaps are introduced 15:14:41 .. erroneously. 15:15:02 .. Nigel also mentioned that setting minimum time constraints on an ISD might reflect refresh rates etc. 15:15:17 .. I'm not so concerned about this because there's already text about the refresh rate possibly not being 15:15:25 .. as fast as needed to show every ISD. 15:15:30 .. Those are my thoughts. 15:16:13 Nigel: Thanks for that. How would it work here if there were a 25th of a second gap between two 15:16:17 .. non-empty ISDs? 15:16:21 q+ 15:16:39 Pierre: The switch would open, so nothing would be available for display, at the end of the non-empty ISD. 15:17:23 .. While the previous non-empty ISD is being displayed, the next non-empty ISD is being drawn into 15:17:38 .. the alternate presentation buffer. When the very short empty ISD occurs, the switch opens, 15:17:45 .. independently of the presentation buffer. 15:18:02 .. When the empty ISD ends it closes and the next non-empty ISD, drawn into the alternate presentation buffer, 15:18:27 .. is moved into the active presentation buffer and is displayed. 15:18:31 ack at 15:18:52 Andreas: When a non-empty ISD follows another non-empty ISD the presentation buffer will stay as it was 15:19:06 .. before, but it will be toggled so nothing is sent to the display. 15:19:20 ..s/display./display? 15:19:23 Pierre: Exactly. 15:19:40 Andreas: When a non-empty ISD comes up is there an additional action to clear the display? 15:20:00 Pierre: The assumption is that it costs nothing to display nothing. 15:20:18 .. In a traditional graphics system with a graphics plane with a front and back buffer, the assumption is 15:20:30 .. that disabling compositing with the graphics plane is a zero cost operation. 15:20:35 Andreas: OK 15:20:41 Pierre: In modern systems that is true. 15:21:27 Andreas: Maybe there is no cost associated with it, but you may have to delete a DOM node or whatever, in HTML, 15:21:32 .. so there is something that needs to be done. 15:21:41 Pierre: If you're using cues, when no cue is displayed there is no work. 15:21:54 .. There's work in preparing a non-empty cue but there's no such thing as an empty cue, just no cue. 15:22:30 Andreas: That's right, but there is no duration with the ISD that you send to the display, right? 15:22:46 Pierre: The way the HRM is written, the output of the presentation buffer is "made available" to the display. 15:23:01 .. That's really broad, "display", here. It depends on how fast the output rendering device can go. 15:23:17 .. The HRM says today that it is conceivable that a non-empty ISD, that has content, is so short, that it will 15:23:33 .. never be displayed because it comes between two refresh cycles of the display. That's already acknowledged 15:23:35 .. by the HRM. 15:24:10 Nigel: If I understand right, this model will not catch very short empty ISDs? 15:24:15 Pierre: I've agonised over this. 15:24:31 .. I really like the idea of catching errors, making an integrated SHALL statement in the model. 15:24:47 .. But even with non-empty ISDs we can't guarantee they will be displayed. 15:25:09 .. I've been agonising about a SHALL or a SHOULD for the minimum duration of a sequence of empty ISDs. 15:25:27 .. The other question is what should the lower bound of that duration be? 15:25:42 .. Another important point for the notes: 15:26:02 .. Going back to the minimum duration of empty ISDs, I'm uncomfortable: 15:26:21 .. Netflix has a min duration of 2 frames, I've heard 3, maybe 1, but nobody ever says what the frame rate is! 15:26:28 .. So I'm not sure what the right lower bound is. 15:26:50 .. Having a SHOULD for any validator to warn if there is an empty ISD shorter than 1/30s, but making 15:27:03 .. it a normative SHALL requirement is another thing. 15:27:23 Nigel: That's a strong argument: if we don't have data points to support SHALL statements we ought not to have them. 15:27:42 Pierre: A SHOULD would not be bad to have, but it would be a heuristic. I'd say right now, that neither 15:28:14 .. 608 or STL can have gaps shorter than 1/30s but it is possible with EBU-TT-D say. 15:32:20 Nigel: [asks about the edge case of a very short non-empty ISD and empty ISD followed by a non-empty ISD] 15:32:37 Pierre: The cost of clear is still present for erasing the presentation buffer, that doesn't change. 15:32:42 Nigel: Yes, I see. 15:33:04 Pierre: The minimum duration of a non-empty ISD has not changed. 15:33:28 Nigel: No, it has, because it now also includes the duration of a following empty ISD whereas before it did not. 15:34:25 Pierre: Right, absolutely, you could have a non-empty ISD that's a millionth of a second followed by a 15:34:37 .. relatively long empty ISD - before, that was not possible. 15:35:11 Nigel: Worth noting, it may already be present, that this is not about the readability complexity, 15:35:16 .. but the presentation complexity. 15:35:30 Pierre: I'm going to note that, maybe make sure there's a statement like that in the document. 15:35:44 .. I'll update the pull request. 15:35:50 Nigel: Thank you! 15:35:57 Pierre: Thank you for hearing me out. 15:36:15 SUMMARY: @palemieux to update the pull request 15:37:02 Topic: Rechartering Formal Objection Council status update 15:37:23 Atsushi: No update, it's possible that in the next few hours I will hear back. 15:37:33 Pierre: Thank you for that. 15:37:58 Atsushi: The latest document for FO is at the same URL as the previous one so you can see the FO Council report. 15:38:45 -> https://www.w3.org/2022/09/ttwg-charter-fo-report.html Team Report on Timed-Text WG Charter Formal Objection 15:39:06 Nigel: Thanks, that incorporates the Chairs response from me and Gary. 15:39:40 Topic: Meeting close 15:40:08 Nigel: Thanks everyone, that's completed those parts of the agenda that we could do today. 15:40:17 .. Let's adjourn a little early. [adjourns meeting] 15:40:36 rrsagent, make minutes 15:40:36 I have made the request to generate https://www.w3.org/2022/10/27-tt-minutes.html nigel 15:41:07 s/in the next few hours/in near future/ 15:42:42 s|s/display./display?|| 15:42:49 rrsagent, make minutes 15:42:49 I have made the request to generate https://www.w3.org/2022/10/27-tt-minutes.html nigel 15:45:04 s/nothing is sent to the display./nothing is sent to the display? 15:45:05 rrsagent, make minutes 15:45:05 I have made the request to generate https://www.w3.org/2022/10/27-tt-minutes.html nigel 15:45:59 scribeOptions: -final -noEmbedDiagnostics 15:46:03 zakim, end meeting 15:46:03 As of this point the attendees have been Nigel, Pierre, Andreas, Atsushi 15:46:05 RRSAgent, please draft minutes v2 15:46:05 I have made the request to generate https://www.w3.org/2022/10/27-tt-minutes.html Zakim 15:46:08 I am happy to have been of service, nigel; please remember to excuse RRSAgent. Goodbye 15:46:13 Zakim has left #tt 15:48:45 rrsagent, excuse us 15:48:45 I see no action items