W3C

Timed Text Working Group Teleconference

21 Jul 2016

See also: IRC log

Attendees

Present
Nigel, Mike, Andreas, David_Ronca, Philippe
Regrets
Thierry, Frans, Pierre, Glenn
Chair
Nigel
Scribe
nigel

Contents


<scribe> scribe: nigel

This meeting

nigel: We are low on numbers today for various reasons. What are we quorate to discuss?

mike: Perhaps a brief update on the IANA registration

Andreas: TPAC
... Also the lineHeight, background height issue and the need for a solution.

nigel: Okay, I'd also maybe like to come back to the Safe Crop Area proposal.

TPAC 2016

nigel: Note that the hotel closest to the venue is getting low on availability: I just tried booking and failed!
... So it's worth booking accommodation soon.

Andreas: Regarding the conflict (for some) with the Web & TV IG meeting on the Monday
... and the TTWG meeting on the Monday and Tuesday. There is some overlap of interest
... so this is unfortunate. It may be difficult to change this, but we should ask the Web & TV IG
... at least about their agenda so we can have a basis for setting our agenda topics.
... Also we thought about a combined meeting with the Web & TV IG. I'm not sure if this
... is still of interest for others. There's clearly an overlap in what they are working on,
... and also the members are I think interested in progress on the subtitle front. It could
... be a possibility to discuss the issues about WebVTT and TTML and the adoption of
... IMSC.

nigel: For the last few years we have provided an update to the Web & TV IG who are
... indeed interested in our progress, so I think it makes sense to ask for some joint time
... with them so that we can do the same this year. I'll give myself an action.

<scribe> ACTION: nigel Contact the chair of the Web & TV IG to ask about schedule and joint meeting time. [recorded in http://www.w3.org/2016/07/21-tt-minutes.html#action01]

<trackbot> Created ACTION-475 - Contact the chair of the web & tv ig to ask about schedule and joint meeting time. [on Nigel Megitt - due 2016-07-28].

mike: That's a good idea - I won't be there by the way.

davidr: Dae will be there for Netflix - I don't really have an opinion on it.

Profiles registry and TTML IANA registration

mike: If you go to the interaction with IANA link, there's the old one a year or two ago,
... but nothing in there that indicates that we have any open engagement with IANA. I
... thought plh had done that but it looks like not. We've had no response from IANA either.

nigel: Okay, it looks like something's "stuck". I have prompted plh but it's unclear what's happening.
... Ideally he'd be on the call...
... I've sent him a message to see if he is available to join. If he can let's come back to this.

TTML issues

nigel: Andreas, I think you wanted to mention lineHeight etc?

andreas: We discussed this for 3 weeks with a lot of discussion and comments, then
... other discussions took over. I think it's important that we look for a solution because
... HbbTV has now published an update to their spec and they have some normative
... text that clarifies this issue and I think they also are waiting for clear guidance from
... W3C or EBU that they could reference, but because they have to publish sooner they
... needed to include some text. I think it's important for us to check this change and
... also to work on the solution and decide if there's an errata needed for TTML1 or an
... update to IMSC 1 and how in general this should be solved for TTML2.
... It may also be important but out of scope for W3C that HbbTV starts a liaison with W3C
... on this issue.

nigel: Can you recall what HbbTV did?

andreas: They made a lightweight addition, based on a request that a transparent gap
... should not appear between line backgrounds. So the solution is that for lineHeight <= 125%
... when the background is set on consecutive rows there should not be a gap between
... the line backgrounds, without explaining how the renderer should make that happen.
... The solution for how this conceptually and theoretically would be done in TTML is still
... outstanding and the task of this group.

nigel: Even this group may not be the best place to fix it - sometimes we have to do so
... when nobody else will fix it, but it seems like it should be fixed in CSS and then we should
... align with that, otherwise it's a bit backwards.

andreas: It would be good to have a pragmatic solution as soon as possible so that the
... different standards are compatible with us, e.g. by an errata with TTML1. Going back
... to the discussion we had there was I think not a really clear view of the group how this
... case should be handled so there seems to be a gap in TTML1 how it should be handled.
... If this is the case that there is some room for interpretation then there can be an errata
... in TTML1. If this is not the case then it would be good to have a solution in the next
... upcoming spec, which could be an update to IMSC 1.

davidr: I've seen that separation between backgrounds of multiple lines of text is a problem
... on iOS with WebVTT.
... For our TTML clients we don't specify backgrounds.

nigel: Our BBC subtitle guidelines take the opposite approach - a black background is
... required and there must not be gaps between lines, so this is a real issue for us.
... Thank you for raising the profile of this once again.

Profiles registry and TTML IANA registration (continued)

plh: I started the review - IETF says we have to start the review on their TIES mailing list
... first. You have to do a complete submission every time.
... Once we're done we send the request to IANA.

nigel: Is the IETF review period open ended or will it close?

plh: It is open ended; it's been more than a month but I would think that is enough.
... I would not worry about the time period. But I would ask if we addressed the comments?

mike: The status is: we received 2 comments from W3S; one was rejected by the WG

plh: I'm not aware of W3S comments on the IETF list.

mike: I'm not aware of any comments from the IETF list.
... There was a comment from Eric Prud'hommeaux and Paul Libbrecht who posted to the public TTWG reflector
... and those are the only two comments.

plh: [looks on the IETF list] If the comments are not on the IETF list then they are not a concern.

<plh> https://lists.w3.org/Archives/Public/public-tt/2016Jun/0012.html

plh: That's my request on June 16, which I sent to the IANA media types list, as required.

<plh> https://lists.w3.org/Archives/Public/public-tt/2016Jun/0014.html

<plh> https://lists.w3.org/Archives/Public/public-tt/2016Jun/0015.html

plh: So one comment was rejected?

mike: We decided not to proceed with the Mac clipboard type request.

<plh> answer to Paul: https://lists.w3.org/Archives/Public/public-tt/2016Jun/0018.html

mike: Nobody expressed any interest or practice that we could codify.

plh: So did you do what is needed to address the comments?

mike: Eric's comment was editorial, but I didn't want to edit the document until the review
... period is over.

plh: At this point I need the document to be updated so I can submit the registration to
... IANA itself.

mike: Okay I'll make the changes via issues and PRs and send you an email when I'm done.

plh: Then let me know when you're done and email me until I've sent it to IANA!
... The form I will fill is at:

<plh> http://www.iana.org/form/media-types

plh: Sometimes the hardest question to answer is "encoding consideration" so if you think
... it is perfectly answered in your document then you're fine.

<plh> "Encoding Considerations"

mike: All the comments are on the note not the media type registration. We didn't touch
... that aside from adding a codecs parameter.
... I can't understand why the same answer would be a concern now when it wasn't before.

plh: Understood. When I send the form to IANA then, according to my most recent experience,
... they're pretty fast in processing it.

mike: I understand the steps - I'll make the edits and send you an email later.

plh: Thank you.

nigel: Thanks both - great to unlock that.

TTML issues (continued)

nigel: I'd like to come back the BBC's Safe Crop Area proposal - noting that the people
... present today are a mutually exclusive set relative to those present last week when we
... discussed it.
... I don't know if anyone has had a chance to look through it. Mike, thank you for
... sending through the links to smpte documents.
... I think they help to explain how the problem arises but do not solve it.
... [outlines problem of trying to maintain positional registration and complete display]

mike: There's both a display problem and an authoring problem.
... There used to be something like a safe area in the video, not directly solving the
... problem for subtitles and captions. The active format descriptor and bar data help
... to describe the status for video, and SMPTE is in the process of updating those.
... It helps solve the video problem and may provide a framework for how we want to fix
... it for TTML. There's also ISO/IEC 14496-30 corrigendum 1, which tries to provide
... some signalling outside the document, which we should look at.

nigel: It was unclear to me what that corrigendum actually means for the decoder.

mike: It's about the aspect ratio of the TTML and the active format descriptors describe
... how to ignore deliberately black areas even though they're encoded in the video.

nigel: What this proposal does is to defer some of the solution space but provide extra
... information to allow decoders to do a better job.

davidr: At this point we don't deal with the use case of subtitle registration differing from how it is authored.

nigel: Okay, well I encourage everyone to look at the proposal document
... https://lists.w3.org/Archives/Public/public-tt/2016Jun/0003.html
... direct link to PDF: https://lists.w3.org/Archives/Public/public-tt/2016Jun/att-0003/Subtitle_Safe_Crop_Area_BBC_submission_2016-06-09.pdf
... If there are no adverse comments then I intend to raise this as an issue and possibly a PR on
... IMSC 1 for a future update, because that is where it would be most useful for uptake.
... Thanks all [adjourns meeting]

Summary of Action Items

[NEW] ACTION: nigel Contact the chair of the Web & TV IG to ask about schedule and joint meeting time. [recorded in http://www.w3.org/2016/07/21-tt-minutes.html#action01]
 

Summary of Resolutions

[End of minutes]

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