IRC log of tt on 2017-05-25

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Meeting: Timed Text Working Group Teleconference
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Date: 25 May 2017
14:02:40 [nigel]
scribe: nigel
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Chair: Nigel
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Present: Nigel, Dae, Pierre, Nigel
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Regrets: Andreas, Thierry
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Present+ Glenn
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Topic: This Meeting
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Nigel: I don't think we have anything to discuss on TPAC today;
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.. on TTML2 there's a request to discuss Audio Description (AD) at the head of the meeting
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.. and we have a bunch of TTML issues and pull requests plus some activity on IMSC.
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Pierre: We have a blocker for pull request #230 so we can not close that until we have
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.. resolved the bigger question in TTML1.
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Nigel: The HDR in PNG is currently paused awaiting feedback so we should cover that
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.. briefly.
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.. Any other business or points that anyone wants to make sure we cover today?
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group: [silence]
14:09:51 [nigel]
Nigel: OK that's our agenda.
14:10:38 [nigel]
Pierre: I'm not opposed to AD today but without Mike and Andreas being present it might
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.. need to be repeated later.
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Dae: I see that Mike has views on this too.
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Nigel: I've had private conversations with Mike about AD and I think he has reservations
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.. but is willing to accept it, probably.
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Topic: TTML2 - Audio Description
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Nigel: In terms of a walk-through, the first thing is the Requirements:
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-> Audio Description Requirements
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Nigel: These were circulated in September and revised following feedback in October to
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.. establish the alignment with the MAUR requirements covering the same space.
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.. It is envisaged that, workflow-wise, small additions to TTML2 would satisfy any subset
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.. of the workflow described.
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Pierre: [concerns about the ability for TTWG to influence distribution formats]
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Nigel: [commitment from BBC to produce an open source implementation showing how
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.. client side mixing could work in a browser] No intention to require or request that
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.. TTML2 is used as a distribution format for AD.
14:23:49 [nigel]
Glenn: Doing integration work to add audio into TTML2 it became clear that the semantics
14:24:07 [nigel]
.. for audio were incomplete. TTML has requirements for text to speech.
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.. Adding further functionality that completes the audio semantics and also happens to
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.. satisfy the ability to provide the audio description service requirements is something
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.. we should do to make audio work in TTML. This is the wrong time to be making a
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.. decision about whether to include these new features - if it goes into the spec then
14:25:59 [nigel]
.. we have a process for figuring out if it stays in beyond CR, based on implementations.
14:26:33 [nigel]
Nigel: Thanks both. So that's a quick summary of the requirements, then in the issue:
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-> Add support for Audio Description requirements
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Nigel: I describe some specific semantic requirements for TTML2.
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.. [describes the audio processing model being proposed]
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.. Map from a TTML2 element structure into a Web Audio graph
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.. Additionally I see that text to speech semantics were added by Glenn subsequently,
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.. which is fine.
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Glenn: My audio model for TTML is quite simple. Right now TTML produces a series of
14:32:31 [nigel]
.. raster images typically on visual presentation medium. It does not yet have an audio output,
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.. but it certainly can. All of the equipment that I'm looking at in terms of supporting the
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.. audio feature set basically ends up producing a single audio output stream similarly
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.. to how the visual rendering part of TTML produces a single motion picture output.
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.. That would be the more generalised output. As for the model for processing audio, I'm
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.. currently assuming that it's possible to do it all in software but that implementations
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.. could optionally use hardware features to optimise and improve efficiency. For example
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.. mixing, panning, text to speech synthesis, I'm assuming it is possible to do all these in
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.. software in a presentation engine.
14:34:22 [nigel]
Nigel: There's good evidence for that by the way.
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Glenn: On some devices that may be impractical, just as it may be impractical to do
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.. visual compositing and HDR color on some devices.
14:35:25 [nigel]
Nigel: Thanks Glenn, that's the summary. Any other questions?
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Dae: It seems like it won't be in IMSC2. If AD is threatening the timescale of WR, are we
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.. agreed to remove it?
14:38:26 [nigel]
Nigel: I agree that it would not be in IMSC 2. I'm not happy to agree with removal from WR at this stage.
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Dae: [question about handling of WR comments and if they are prioritised for audio
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.. relative to other features]
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Nigel: No specific priority given for or against any feature set including audio.
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Glenn: I think we should not talk about this in terms of AD but just in terms of audio
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.. features. We should just be focusing on generic audio.
14:44:07 [nigel]
Nigel: +1 to that - in terms of profiles, we may later want an AD in TTML2 profile based on
14:44:18 [nigel]
.. the audio semantics in TTML2, so that is the point when we should discuss AD more
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.. specifically.
14:44:45 [nigel]
Dae: [question about removing features, and when in the process to do this]
14:50:39 [nigel]
Nigel: Typically we would not remove features unless they are at risk in CR and they
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.. prevent us meeting the CR exit criteria, in which case we would remove them to move
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.. to PR.
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.. Conversely during WR we need to agree a disposition of all received comments, and if
14:52:17 [nigel]
.. in extremis we get feedback explaining that we have a big technical problem with a
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.. feature then we could agree to remove that feature prior to CR.
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Dae: [does not want to extend the publication period for WR]
14:57:21 [nigel]
Nigel: I have committed to put effort into getting the audio features in within the agreed
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.. timescales for WR.
14:57:47 [nigel]
Pierre: [queries expertise in group for dealing with audio and DA
14:57:52 [nigel]
14:58:07 [nigel]
Pierre: and ability to specify this and influence industry]
14:59:05 [nigel]
Nigel: [does not consider there to be a specific requirement for vendors to be members
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.. of the group]
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Dae: [concerns that a large number of audio-related comments during WR could delay
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.. onward progress]
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Nigel: We've discussed this for about an hour now, let's take a break and reconvene in 5
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.. minutes and begin with the TTML issue that's also blocking IMSC.
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Topic: LWSP between non-terminal components of style and parameter attributes
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-> Required spaces between non-terminal components of styling and parameter attributes (issue #221)
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-> LWSP in rgba expressions?
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Nigel: Interesting there's no TTML1 issue.
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Pierre: It looks like we have to solve this in TTML1 to make progress in IMSC.
15:10:40 [nigel]
Glenn: I think there's a fair consensus at this point (to verify) that white space around
15:10:56 [nigel]
.. COMMA in tts:fontFamily is probably justified in TTML1, but not in RGB expressions.
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.. The justification is based on actual usage; we have plenty of fontFamily examples where
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.. there is white space but I cannot find any in RGB expressions in TTML, though there are
15:11:43 [nigel]
.. plenty in CSS. My suggestion is we add a note to TTML1 clarifying that LWSP is permitted
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.. around commas in fontFamily and another emphasising if necessary that it is not
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.. permitted in RGB expressions. I have a different answer for TTML2 however.
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Nigel: Would that work in TTML1 Pierre?
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Pierre: I'm not sure I'm there yet. There's evidence for spaces in fontFamily so we have to
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.. deal with this. What's not clear in my mind is if the revised TTML1 text should say that
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.. spaces shall not be there but by the way there's evidence of documents with spaces,
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.. therefore processors should be tolerant. Or option 2 is to say spaces are permitted but
15:13:32 [nigel]
.. some processors may reject them. I'm not sure it's clear to everyone. We need an issue
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.. in TTML1 and reference it.
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.. [creates issue]
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-> Handling of LWSP in tts:fontFamily #248
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Nigel: The next step is to solicit feedback?
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Pierre: Yes, or to make a call if no feedback is received.
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Nigel: As a strawman I would propose to adopt the second option as a default, i.e. to
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.. permit LWSP in document instances.
15:21:18 [nigel]
Pierre: I don't have a strong opinion - I need to discuss it with others.
15:21:33 [nigel]
Glenn: I do have a strong opinion, which is the second option, to permit LWSP in document instances.
15:22:06 [nigel]
Nigel: I will add each option as a separate comment in the issue so people can add a +1
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.. reaction to the option they prefer.
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.. They're now added on #248.
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Nigel: Is there anything else we can do to unblock that issue now?
15:23:46 [nigel]
Pierre: No, if you know vendors or users I would encourage them to weigh in on that issue.
15:24:14 [nigel]
Glenn: Skynav will be able to point to 4 independent implementations that the second
15:24:21 [nigel]
.. option is the better one, going back to 2004 timeframe.
15:25:25 [nigel]
Topic: IMSC Pull Request 229
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-> Remove tabs from examples (issue #225) #229
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Pierre: I'm waiting for your input Nigel.
15:25:49 [nigel]
Nigel: Apologies, thank you for the reminder.
15:27:16 [nigel]
Glenn: I think you should remove the white space at the ends of the lines.
15:27:49 [nigel]
Nigel: Is this example supposed to test functionality in the presence of white spaces at
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.. the ends of lines?
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Pierre: No.
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Nigel: In that case we should make them as simple as possible so we should remove the
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.. whitespace at the ends of the lines. I will update the PR.
15:28:58 [nigel]
Glenn: I agree that extraneous content should be removed from examples, more generally.
15:29:06 [nigel]
Nigel: I've added a comment to the pull request.
15:29:25 [nigel]
Topic: PQ HDR in PNG
15:29:56 [nigel]
Nigel: I raise this topic just to note that there is a strong objection to the current approach
15:30:06 [nigel]
-> ICC profile contents are ignored, magic string used for labelling #3
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.. Please look at the issue and the linked thread in the Color on the Web CG reflector.
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s/Nigel P/Nigel: P
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Pierre: I've tried to get to the bottom of what was concerning Chris because it was not
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.. clear and it sounds like the main concern was the implication in the proposed Note that
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.. prohibits use of the embedded ICC profile, which is not what it was meant to mean.
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.. I have offered to clarify it so that it does not imply that at all.
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.. As far as I can tell that is the concern. It is possible that an ICCMax profile might be
15:33:00 [nigel]
.. better, and that could be added later. My main blocker is getting an ICC profile that
15:33:19 [nigel]
.. does not have an Adobe copyright, so that's what I'm working on right now.
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.. When I get that updated profile I will commit it, and I've encouraged Chris to revise his
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.. issue to be more specific. In the absence of that I will create a pull request that hopefully
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.. will satisfy Chris.
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Nigel: I think it would be reasonable for me to ping Chris with a reminder tomorrow, given
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.. that I proposed a week's review 6 days ago.
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Pierre: If he can't agree to that review period then we can say that when we have resolved
15:35:34 [nigel]
.. the copyright issue we plan to move forward, which sets a new effective deadline for
15:35:39 [nigel]
.. expressing his concerns.
15:36:38 [nigel]
Topic: Logical vs Physical pixels
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Pierre: Have we got anything more to discuss on this?
15:36:59 [nigel]
Glenn: Last night I did a subsequent edit, and I believe it is all resolved now.
15:37:10 [nigel]
.. I took out unreferenced terminology for example everything with Viewport.
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Pierre: Ok great.
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Glenn: I also took others out like dot pitch, storage units, sample units and substituted
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.. logical pixels. I took out the word "physical" and used the word "display" pixels and
15:38:15 [nigel]
.. referred to hypothetical output devices as opposed to actual output devices.
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Nigel: Is this in a pull request?
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Glenn: It has been merged already.
15:39:04 [nigel]
-> Apply improvements to aspect ratio and pixel semantics. #321
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.. There is one open issue on the definition of "contain" .
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.. Issue 30 has now been closed.
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s/Issue 30/#30
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Pierre: It sounds like we ended up in a place where the root container coordinate system
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.. is all logical, right?
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Glenn: Right. We ended up with logical pixels and display pixels and logical pixels have
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.. no aspect ratio, but that there's a logical transformation via PAR that creates display
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.. pixels from logical pixels.
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Pierre: Why have two terms?
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Glenn: In my mind you author into logical pixels and there's a transformation process that
15:41:48 [nigel]
.. turns them into dimensioned pixels, and I feel that's an important concept to retain.
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.. I am also trying to converge with the SVG model.
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Pierre: I think we're very close to having logical coordinates.
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Glenn: Please review the changes and raise issues.
15:46:21 [nigel]
Nigel: I've just found a broken link in 10.2.33 to presentation context coordinate space.
15:46:30 [nigel]
Glenn: That's a link I removed so thanks, I'll resolve that today.
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Nigel: Ok that's an action on all to review.
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-> deprecate use of pixel units unless tts:extent on root element is in pixels #330
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Glenn: Is there anyone who disagrees with this issue?
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group: [silent]
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Glenn: I'll take that as tentative support.
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Topic: TTML issues
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-> revert deprecation of ttp:profile on root element #331
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Nigel: I've commented on that.
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Glenn: Okay I'll look.
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Nigel: I think there's evidence that people are trying deliberately to target multiple
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.. processor profiles.
15:50:54 [nigel]
.. Is there any possibility of extending the value space to allow the short codes?
15:51:34 [nigel]
Glenn: I doubt that, due to the use of URI.
15:52:45 [nigel]
.. Right now it is deprecated, we are just talking about undeprecating it.
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Nigel: To me undeprecating it could be improved maybe by extending it too. I'm not hugely
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.. concerned.
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Topic: TTML progress tracking
15:53:43 [nigel]
Glenn: We are getting near the end of May. We plan to have everything at least in pull
15:54:01 [nigel]
.. request form, so I will work this week to knock off the 24 items on my list. I have been
15:57:19 [nigel]
.. taking things off my list that have no pull request.
15:58:06 [nigel]
Nigel: Please do not close issues just because you do not intend to work on them. We will
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.. leave issues open so that people who want can pick them up until we decide to
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.. assess the open issues and choose to close or defer those we do not have work for.
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.. The reason for leaving issues open is to signal that work is needed.
15:59:04 [nigel]
Dae: There are 18 features that need image example - I may need help with those.
15:59:35 [nigel]
Nigel: Okay, feel free to send a message to the group reflector listing those or send the
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.. list to me and I can include it in the agenda that I will send on Tuesday.
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Nigel: Do you also need the example documents from which to generate the images?
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Dae: That would help.
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Nigel: We're out of time for today. Thanks all. [Adjourns meeting]
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