Meeting minutes
This meeting
Nigel: Today our agenda is:
… TPAC 2023 reflections
… IMSC-HRM - do we have anything to cover on this today?
IMSC-HRM review feedback
Pierre: We received feedback from one content provider, which was positive.
… I am working with three others.
… So far, it's been pretty good.
… Bugs were found in the reference implementation, which were fixed.
… There are also bugs in some content providers' libraries.
… I'm cautiously optimistic that there are no major issues with the spec itself.
… Now everybody is back from IBC and vacation I'm going to try to get it done by end of October.
Cyril: You said one provider - that's Netflix, right?
Pierre: Yes, the only one who has provided feedback to the group.
… One of the three others has provided me with some results privately.
Cyril: I don't know what we decided - when we did the test Nigel there were bugs, but that's okay.
… The Netflix content did not invalidate the IMSC-HRM model, so it is probably good.
… One thing we found that was interesting, but still does not jeopardise the model,
… for some content, Netflix produces content with very small cues - I ran about 3000 pieces of content -
… and we decided the content should have been authored differently.
… The issue is with 2 speakers speaking almost at the same time, they have cues that overlap,
… but not completely, in time.
… If you have 2 speakers, one speaks, then the other starts speaking, then the first stops,
… Netflix splits that into 3 non-overlapping ISDs. If they are very short, that was creating a
… content validation error according to the HRM.
… I suggest we keep that as an issue and keep talking about it.
Pierre: Yes, I think that's worth discussing.
… The bottom line is that the HRM model does not assume that the renderer can detect identical
… regions or parts of ISDs.
Nigel: It does assume some level of caching, at least.
Pierre: Yes but it has no notion of identical content, so background redraws are not cached, for example.
… I'm not sure it's a problem.
… The Netflix approach, which Cyril will raise as an issue, was introduced to work around some
… limitations of some clients.
Nigel: I think we just completed that agenda topic!
Agenda continued
Nigel: We may also have a few things to discuss on DAPT.
… In AOB, Andreas sent an email reminder about the DVB liaison, and I have responded
… on the member-tt list. Not sure if we have anything more to discuss during this call?
group: no request to discuss further today
Nigel: Is there any other business, or points to make sure we cover?
Pierre: What's the plan wrt that liaison?
Nigel: Let's cover in TPAC 2023 reflections
TPAC 2023 reflections
Nigel: Just want to open up to any thoughts or observations anyone had?
… I should comment about the joint meeting with APA WG and MEIG on the Thursday afternoon.
… We had a good discussion, and it included the liaison from DVB, which APA WG was interested in also.
… Since the liaison wasn't clearly targeted at any one group, but several might be interested,
… I asked for a single team contact to bring together the responses and look after sending them.
… François (tidoust) offered to do this or identify someone else who would.
… In that context I think we should bring him in on the reflector discussions.
… Does anyone have any comments on the response draft from Andreas and my reply?
Pierre: Yes, sounds like a good idea to refresh our collective memory.
DVB Liaison (member only reflector link)
Nigel: [iterates through the liaison input]
Pierre: On the point of audio track language, and the interaction between the audio signalled in the
… content and user preference, I think any metadata document that describes what to signal in the content
… is not useful unless there's an algorithm indicating how that metadata is used by the client.
… There are subtle interactions between choice of language on the client, whether or not the client
… has indicated it would like captions or subtitles, and there have been attempts at doing that.
… it's a surprisingly really hard problem.
… It would be great to standardise something, and the algorithm should be standardised to, for the client.
Nigel: I would like to say that too.
Pierre: We should say it plainly: unless there's an algorithm that specifies the interaction between
… user choices and signalling then it is incomplete work.
… There was an algorithm created back in the Ultraviolet/DECE days, and it's quite complex.
Nigel: Yes, I tried reading that once!
Pierre: We should really emphasise that point.
… It's particularly important when forced narrative is available.
Nigel: Yes
… Any more on that, or on TPAC more generally?
Pierre: On TPAC more generally, I was there for the discussion about Apple's suggestion on an API
… for improving TextTrackCue. Do you know if this is going to be turned into an effort within this
… group or another group?
Gary: I think it's on Apple to take the action of updating all the relevant specs like HTML, WebVTT etc
Nigel: They have opened the above pull request on HTML.
… There's a lot of HTML spec complexity in there, but in terms of the basic requirements I have
… added a couple of comments, and recommend others review too.
Nigel: The issue I have with this now is that without full CSS support for fillLineGap and linePadding I don't know how we could use it.
Pierre: In creating imscJS we spent a lot of time working out how to make it match the TTML expectations.
… I'm not aware of any effort being done to validate this API, is my summary.
Gary: From my understanding, the API doesn't preclude any of that, the only change in IMSC is to add
… the attribute tags to the output HTML from imscJS, so the styling should just be carried over.
Pierre: I can believe that theoretically, but we need to see a comparison between the rendered output and
… the test references.
Gary: I guess that's part of getting the pull request approved.
Pierre: The reason I'm raising it is that HTML and CSS and TTML are each complex.
… I've surprised myself in the past with corner cases.
Gary: They brought up that there can be conflicts between the user setting overrides and the
… IMSC presentation. That's another issue - they said there's nothing they can do about that.
Nigel: Two things. Firstly, without CSS support for fillLineGap and linePadding, I think it will be impossible
… to make the tests all render correctly, because the imscJS code that works around those HTML and CSS
… limitations cannot run without the HTML fragment being homed to some DOM element.
… And in the proposal, no client code can run on it when that is the case.
… Secondly, if CSS support were added for those features, then that could work around some of the
… oddities that could result from user settings being unexpected, in respect of those two styling features.
… I haven't even thought about ruby and text decoration but I think that ought to work, in principle.
… So maybe the feedback to Apple is yes, but we need CSS support for those missing features.
Gary: Yes, and I think that was discussed and maybe we need to bring that in more strongly that as
… part of this the CSS related discussions need to be restarted.
… To the first point, potentially, and I guess this is the question, the document fragment we give to the API,
… there's nothing disallowing it from being added to the DOM first to apply the workaround beforehand.
… Theoretically this could be done, as a workaround.
Nigel: Yes, though if the user makes the text size bigger then it would break.
Pierre: I don't think anyone has implemented imscJS this way and tested it fully.
Gary: I think Eric did implement it this way, but maybe did not cover all the edge cases.
Pierre: This API is definitely a bit different from what I saw 4 or 5 years ago.
Gary: I don't disagree that a lot more testing is needed, especially with more complex inputs.
Nigel: Sounds like an action to land this point somehow, not sure who is best placed to do so.
… I'm certainly happy to send a message to Eric and James from Apple, as well as Marcos.
Gary: Final point: they link to some tests they wrote for WebKit in their PR, but it does seem to be on the simple side.
Nigel: Any other TPAC discussion points?
group: none
IMSC-HRM
Cyril: What are the next steps to move forward?
… One more content provider reporting and that is it?
Nigel: Good question - what are the exit criteria?
… We have tests
Pierre: Yes.
… I think we need 2 content providers. We have one.
… I'm hoping that we can, in a month, decide whether or not we need changes.
Nigel: [reads CR exit criteria at https://
Cyril: So we already meet the criteria?
Nigel: Apparently so, though in the weakest way we possibly could!
Atsushi: I'm not sure what the first criteria means - do we need a content document
… produced by a content producing implementation and validated by a content validator,
… but I am not sure. We have a manual set of test suites and validated by [scribe missed]
… but if current criteria are that the same document needs to be produced by one implementation
… and validated separately, then we need some other set of content.
Nigel: We discussed at the top of the meeting, and mentioned that Netflix has an implementation
… that they have verified by processing about 3,300 documents through the validator.
Atsushi: That's great!
Cyril: I did send an email. There were ~20 languages, some subtitles for deaf and hard of hearing,
… some forced narratives, some translation subtitles.
Pierre: As another data point:
<pal> From another content platform: I ran the tool over the weekend on 25,000 randomly selected samples from our library. I recorded 100 failures and I have attached the output of the tool for those failures.
Pierre: I'm trying to get them to release those results.
… So far I think all the failures are in the files themselves. That gives a sense of the scale.
… 25,000 TTML files.
… So far all the failures were errors in the TTML that probably came from errors in translation from 608,
… by my guess.
Nigel: Syntactical errors, or something like that?
Pierre: Not sure what you'd call them - for example, timestamps in hh:mm:ss:ff and the frame counter
… goes beyond the frame rate, e.g. if 30fps, and a frame count of 30!
Nigel: Occasionally we see errors like that too in our tooling in the BBC, which we do catch.
Pierre: We are trying to complete the CR exit criteria report by the end of October.
Nigel: Yes, good idea, let's try to get this completed soon - does that timescale work for everyone?
… I'm going to record assent by silence here!
… That's great, gives us about a month to verify that we have met the exit criteria.
DAPT
Nigel: I have one question - anything from you Cyril?
Cyril: Wide review inputs
Nigel: Yes, I have been making the point generally, on email and to people at IBC, that now is the time
… to review the spec and provide comments, while we're in WD and more easily can make changes.
… I did talk to 3 or 4 organisations about DAPT specifically and some were very positive, and said they
… would either be implementing or reviewing or both.
… It was extremely positive.
Cyril: I did open the TAG review and the i18n review, since we last talked.
… I haven't received any feedback yet, though it has not been long.
Atsushi: For i18n we just reviewed it and resolved it as completed, for information.
… We will mark it as completed shortly.
Cyril: Great!
Atsushi: The action on GitHub might take a little time.
Cyril: I can see that aphilips moved it from in-review to completed an hour ago.
Nigel: One question from me: I thought we had resolved to make langSrc be absent or a language code,
… but couldn't find it documented.
Cyril: Yes we did
Atsushi: It's in our minutes
Gary: You're not misremembering.
Nigel: Thank you! I think the action is on me to implement that, so I will go ahead with that.
… The other thing I wanted to note was that I just opened an editorial pull request in response to an
… issue raised by Andreas, about the definitions of script and transcript, so if anyone can review that,
… it's only small, and that'd be helpful!
<atsushi> https://
Redraft opening section of §2.1 w3c/dapt#183
Cyril: Did you have any feedback from privacy and security reviews?
Nigel: No not yet
Cyril: We discussed removing styles too?
Nigel: Yes we agreed to do that, in w3c/dapt#124
Cyril: The language one was w3c/dapt#148
Nigel: Ah, thank you, I will do that.
Meeting close
Nigel: Thank you everyone, we're at time, and just completed the agenda. Let's adjourn. Be free!
… [adjourns meeting]