Meeting minutes
This meeting
Nigel: [iterates through agenda]. We have a late AOB about the announcement text for
… IMSC 1.2 Rec.
… Any more Other Business, or points to make sure we cover?
group: [no other business]
The codecs parameter should have a formal definition of the use of the combination operators. w3c/tt-profile-registry#71
github: https://github.com/w3c/tt-profile-registry/issues/71
Nigel: [summarises issue]
… I think the semantics are clear but we should check in if we agree!
… The next point is to check where any new text has to go, in the registration text or
… elsewhere in the document.
Mike: codecs is defined by DASH rfc6831 so having a formally defined parameter for TTML
… is going to confuse people. We need a note that this isn't the codecs you think it is, or
… something like that.
Nigel: I half remember discussing this before - we're defining a parameter for the MIME
… type, but the DASH codecs is not part of a MIME type.
Mike: Just a note for now, I will dig around more to see if we need any text about this.
Nigel: Checking in on the semantics,
… this is about signalling processor requirements
… and the + operator means "both things on each side of the operator" are required.
… and the | operator means "either thing is acceptable"
… Then, when both + and | are used, the + has higher precedence,
… so A|B+C|D means any of "A, something that supports B and C, or D"
… and that's it.
… Do we have agreement on that being the intention?
group: [no dissent from this]
Nigel: OK I think we're agreed on that.
Mike: I have a clarification on rfc6381
<mike_> RFC6381 defines MIME type parameters "codecs" and "profiles" for ISO BMFF-wrapped content
Mike: I think its okay because we're in the application/ttml+xml space but we are going
… to need a note that this is for the sidecar native filetype not ISOBMFF.
Nigel: Good point, please could you raise the issue on the repo?
Mike: Sure
Nigel: I think that's orthogonal to defining codecs
Mike: Agreed
Nigel: The next question is where we put the text.
… I'm not sure.
Mike: It's a parameter so it needs to go in the registration text. We're modifying the
… string and the semantics of the MIME type parameter.
Nigel: We're not actually modifying it but we are explaining it better.
Mike: If you put the text in the registration part then it needs to go to IANA, and if you don't
… then that's weird.
Mike: Is this for TTML1 or TTML2 or both?
Nigel: It's both, we moved the registration text into the profile registry.
Mike: I recall now.
Nigel: That's really useful guidance. The last question I have is if we think we must
… define these operators completely with reference to TTML2 profile semantics or if
… we can so it only partially, e.g. in relation to the any() or all() for | and + but with the
… combination only here in the profile registry.
Mike: It seems okay to point to the spec for the definition.
Nigel: I don't want to change TTML2 at this stage.
Mike: It should really be the same.
Nigel: I think there's enough wriggle room there.
Mike: It'd be good if they were the same.
Nigel: This is enough clarity for me to try to make progress. Any other questions or thoughts?
group: [nothing more]
SUMMARY: @nigelmegitt to draft a pull request matching the above discussion
IMSC 1.2
Atsushi: We need to provide some text for a Rec announcement. If we want we may
… coordinate a press release, but we do not need to.
… We need at least some text to include in a news announcement when we go to Rec.
Nigel: Can I ask to work with you on that announcement text Pierre?
Pierre: Of course, how do you want to do it. Shall I take a first pass at it?
Nigel: Yes please
Pierre: What is the deadline?
Atsushi: Release at the Rec. Minimum 2 weeks.
Pierre: I'll aim to have it ready in the next 2 weeks.
Atsushi: I need to request publication of Rec with this text ready for the internal comms
… publication team of W3C.
Pierre: No, where did you post the requested information.
Nigel: I think the answer to Pierre's question is that it's in the agenda issue for this meeting.
Pierre: I found it. All right, I will work on that.
Nigel: One other thing, Pierre, thank you for updating the pull request, I will take a look at
… that change to reference the substantive changes document, and then we should be good
… to merge.
Pierre: That needed to be manually added because it's not part of Respec. It was removed
… from the SoTD when we went back to WD and was never included again.
Nigel: I understand, thank you.
CSS font-matching algorithm may introduce fingerprinting issues w3c/ttml2#1202
github: https://github.com/w3c/ttml2/issues/1202
Nigel: I finally got round to setting up a doodle for this, not everyone has been able to
… respond yet.
Pierre: Unfortunately I cannot make the two current most likely dates. It looks like Sam has the most restricted availability.
Andreas: I agree with Pierre, Sam's availability is most restricted, so maybe we should ask
… him for some proposed slots in the next two weeks?
Nigel: Good idea, I will.
SUMMARY: @nigelmegitt to ask @samuelweiler for additional proposed slots.
Andreas: I wonder if our meeting would be an option too?
Pierre: Regrets from me for Thursday 23rd July, most likely. I'd be available following the meeting.
Nigel: That's an option I could add.
text tracks not supported w3c/media-capabilities#157
Nigel: Mike I think you wanted to bring https://github.com/w3c/media-capabilities/issues/157 to our attention?
Mike: CTA Wave is looking at adopting this work on capabilities and I just took a quick
… look at it because it overlaps with work in ATSC and I wanted to see where it is going.
… I noticed they support audio and video but not text tracks.
… Even if there's only one thing, like the profile, that you get back from this API, it struck
… me as a high level omission. I wanted to know if anyone else had any thoughts about this.
… Exploratory discussion here. I suspect that the reaction will be "do a pull request" when you
… know the list you want to enumerate, or something like that.
Media Capabilities Editor's Draft
Nigel: I think the general intent here is to discover processing "grunt" rather than a more
… general profile discovery mechanism.
Gary: There's a case to be made that if a processor can decode text tracks natively, then
… why not?
… I think they may have left it out because for the initial work the actual decoding of video
… has been the focus because you can't really create a polyfill for it whereas for text tracks
… you can. That may be why they have been focusing on just media decoding.
Pierre: Another wild guess is that often timed text is still processed in JS by the client.
Gary: yes
Nigel: Not what they would consider "hardware" by the platform.
Mike: So you think the focus is more on the silicon capabilities not HTML5?
Pierre: Yes
Nigel: +1
Pierre: Defining "silicon" very loosely there!
… That's just a guess based on what I've heard in the past.
… But that's not a reason not to include timed text, but probably why it did not cross the
… minds of the folk working on it.
Mike: Right, there's effectively a media hierarchy, video -> audio -> timed text
Pierre: I think it's a good idea to raise the issue. There's an issue tracker, so maybe we
… ought to raise an issue.
Mike: I've done that. John Simmons, who is very active in CTA Wave, posted a comment
… that means "it doesn't matter", saying there are no IMSC encoders, which I corrected him on.
Pierre: When the problem really surfaces, then the document will be changed.
… This document came up because somebody was having trouble, say figuring out whether
… to send HDR content to the platform.
… Maybe a way to look at it is when there's a problem, the document will get modified at that time.
Nigel: It turns out that Media Capabilities alone isn't sufficient for player implementations
… to decide which media resources to fetch, because for instance it doesn't tell you the
… screen resolution and frame rate (combined) capabilities. So something else is needed.
Mike: Often people find that a profile alone isn't adequate for describing what media resources
… should be fetched. It could be that profile [of TTML] is enough on its own.
… I wanted folk to be aware of this, it may be we can close in a year with no action.
Gary: Looking at the introduction, it wouldn't respond with a "can play" response to a
… MIME type that isn't audio or video. Because text tracks have mainly been provided out
… of band, the methods don't report back ability to play, so that's why it may not be there.
… It would help if media capabilities would strictly declare it's about processing capability.
Mike: It would be [scribe missed]
Nigel: Think about text track cue timing accuracy too - it could be that low end devices
… have a harder problem with this than high end devices, so it may be useful to signal
… the precision available.
Mike: That's a good point.
Meeting close
Nigel: Thanks everyone for the interesting discussion today. Let's finish a couple of minutes
… early, having completed our agenda. [adjourns meeting]