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CORRECTION to {minutes} TTWG Meeting 28/10/2014

From: Nigel Megitt <nigel.megitt@bbc.co.uk>
Date: Fri, 21 Nov 2014 17:14:23 +0000
To: TTWG <public-tt@w3.org>
Message-ID: <D0952244.16B54%nigel.megitt@bbc.co.uk>
Correction: Under the section IMSC 1 CR Exit criteria the minutes state:

   We will not exit CR before January 16th 2016 at the earliest.


I believe this was a typo and it should read "… January 16th 2015 …".

Please let me know if you understood the minuted date to be correct from your recollection of the meeting, otherwise the correction will stand.

Original section link in HTML format: http://www.w3.org/2014/10/27-tt-minutes.html#item15 reproduced below, without correction:

IMSC 1 CR Exit criteria

   action-345?

   <trackbot> action-345 -- Nigel Megitt to Make request to philip
   and silvia to change living standard to editor's draft. -- due
   2014-11-03 -- PENDINGREVIEW

   <trackbot>
   [41]http://www.w3.org/AudioVideo/TT/tracker/actions/345


     [41] http://www.w3.org/AudioVideo/TT/tracker/actions/345


   close action-345

   <trackbot> Closed action-345.

   nigel: sorry that was the wrong action but it was done!

   action-346?

   <trackbot> action-346 -- Nigel Megitt to Scribe notes on cr
   exit criteria for imsc 1 based on meeting debate -- due
   2014-11-03 -- PENDINGREVIEW

   <trackbot>
   [42]http://www.w3.org/AudioVideo/TT/tracker/actions/346


     [42] http://www.w3.org/AudioVideo/TT/tracker/actions/346


   close action-346

   <trackbot> Closed action-346.

   nigel: Goes through scribed notes - group makes edits
   ... Conclusion is:

   Our criteria for exiting CR will be:

   Provide an implementation report describing at least 2
   independent implementations for every feature of IMSC 1 not
   already present in TTML1, based on implementer-provided test
   results for tests and sample content provided by this group.

   We will not require that implementations are publicly available
   but encourage them to be so.

   We will not exit CR before January 16th 2016 at the earliest.

   pal: That's enough for me to edit the SOTD in the CR draft -
   I'll need to get respec.js to allow this custom paragraph.
   ... The next CR draft may include this text in a weird style
   just to get around respec.js.



From: Nigel Megitt <nigel.megitt@bbc.co.uk<mailto:nigel.megitt@bbc.co.uk>>
Date: Wednesday, 29 October 2014 01:44
To: TTWG <public-tt@w3.org<mailto:public-tt@w3.org>>
Cc: "dahl@conversational-technologies.com<mailto:dahl@conversational-technologies.com>" <dahl@conversational-technologies.com<mailto:dahl@conversational-technologies.com>>, fantasai <fantasai.lists@inkedblade.net<mailto:fantasai.lists@inkedblade.net>>
Subject: RE: {minutes} TTWG Meeting 27/10/2014
Resent-From: <public-tt@w3.org<mailto:public-tt@w3.org>>
Resent-Date: Wednesday, 29 October 2014 01:45

Thanks again to all who attended today's TTWG meeting. The minutes for both 27th October and 28th October are concatenated and available in HTML format at http://www.w3.org/2014/10/27-tt-minutes.html


We made one resolutions today:

RESOLUTION: We will support the EBU line padding proposal with the combination of padding on inline content elements and box-decoration-break.

The review period for this resolution ends on 11th November according to our Decision Process.

Today's minutes in text format:


<trackbot> Meeting: Timed Text Working Group Teleconference

   <trackbot> Date: 28 October 2014

   <scribe> chair: nigel

   <scribe> scribeNick: nigel

   <inserted> Day 2 - Tuesday 28th October

Introductions

   Observers: Noria Sakamoto - Toshiba, interested in broadcasting
   in TTML

   Jerome Cho, LG Electronics - wants to meet FCC regulations for
   accessibility with TTML, WebVTT etc.

   Francois Daoust, W3C, just observing.

   Courtney Kennedy: Engineering Manager at Apple, responsible for
   subtitles.

   Cyril Concolato, University in Paris, GPAC/MP4Box etc

   <pal> Pierre Lemieux, supported by MovieLabs / IMSC1 editor

   Debbie Dahl, Chair of Multimodal Interaction Group, observing.
   Interested in synergies between timed text and EMMA standard

   Kazuhiro Hoya, Fuji TV interested in UHDTV, which will adopt
   TTML for closed caption

   Nigel Megitt, BBC, Chair of TTWG

   Glenn Adams, Skynav. Editor of TTML.

WebVTT draft updated

   [38]http://dev.w3.org/html5/webvtt/webvtt-staged-snapshot.html


     [38] http://dev.w3.org/html5/webvtt/webvtt-staged-snapshot.html


   glenn: Looks good to me.

   Cyril: LGTM. When can it be published?

   nigel: Tuesday next week at the earliest, depending on staff

   Cyril: How will we publicise it?

   nigel: I expect Dave Singer to publicise it to the charter
   dependency groups, W3C and external, and to the W3C liaisons.
   ... Dave has also suggested that we publicise it socially at
   TPAC too.

Spec restyling work (fantasai)

   fantasai: The spec templates and styling over time have become
   outdated - we can use some cool web technologies to make specs
   more readable
   ... The scope of the design is not a back-end web app, just
   HTML/CSS. We want a design for desktop, mobile and print, in
   that order. It will change the markup of the headings
   ... and the boilerplate in the Status text that is data, not
   paragraph text. We'll push legalese to the bottom. The abstract
   should be 2-3 sentences above the fold, then
   ... the TOC available without having to scroll it. Then URLs,
   issues, feedback etc should be at the top in a more compact
   format. So the scope of it is to
   ... redo markup, boilerplate, styling. We'll look at styling,
   clean up the stylesheet to be more readable, make sure that the
   document is still quick-scannable
   ... A lot of styling that is ad hoc, like fragments, example
   code, could be harmonised across all the W3C specs. This will
   take a while - it's a side project for me. We want to take into
   ... account what the WGs need.
   ... The functional questions are [the ones on the agenda]. We
   also want general feedback on what to consider, e.g.
   protocol-relative links so we can switch to https.
   ... or always-visible TOC.
   ... The first question is a subjective/emotional one - what
   should the style express, in terms of values.
   ... If we used primary colours and comic sans it would feel
   like a toy not a spec. But if we used a parchment background
   and old style font it would look old-fashioned.
   ... They're not appropriate for W3C, - we want to know what is
   appropriate though, in terms of how they feel.

   glenn: Do you have any templates or ideas?

   fantasai: We have a proof of concept but we don't know where
   it's going just yet. It's going to be experimental - design by
   consensus. We're asking for ideas from the community.

   glenn: Part of the problem is that you have different audiences
   for different specs.

   fantasai: We haven't had feedback on different styles for
   different document types/audiences. We want them to fit
   together and feel like they belong together.

   glenn: One of the problems is that we have a lot of history.

   fantasai: We want to make sure that every group has a working
   toolset - tell us what you use in response.

   Cyril: Some specs have a developer view and an author view.

   fantasai: Put that under question 6 'what else we should
   know/consider'

   nigel: Can we answer the questions?
   ... Q1. 3-5 adjectives

   Cyril: I have no idea.

   ddahl: Authoritative

   glenn: consistent

   ddahl: comprehensive

   glenn: One problem is that documents don't have the same
   styling. A lot of it is editor-specific.
   ... The variation may cause some problems. I've also worked
   with ISO and ITU which crank out format-consistent specs that
   are somewhat impenetrable.

   nigel: open, welcoming?

   glenn: It would be nice to use newer styling mechanisms. You
   can't push the envelope too far without hitting browser
   variations.

   courtney: clean, modern.
   ... Additional considerations: Should be something that will
   work for low vision people, using magnifiers, voice-over etc.

   nigel: URLs?

   Cyril: TTML1, WebVTT, IMSC 1

   nigel: +1
   ... Do we have documentation of our markup conventions?

   glenn: Not really - we use XMLSpec as a technology (from 1999).
   Others use respec (WebVTT and IMSC 1).
   ... It's very unlikely that we will adopt respec for TTML.
   ... In TTML1 we have a conventions section in the document.
   XMLSpec and Respec are separately documented for markup.

   nigel: Spec processing tools? We've looked at those already.
   Are there any more?

   group: no more

   nigel: Do we have any goals?

   Cyril: To have the table of contents kept visible when
   scrolling, for easy navigation.

   courtney: +1

   Cyril: In some PDF viewers and Word, I like that searched-for
   words are listed as occurrences on a separate panel.

   courtney: Better search would be good.
   ... When I find a page, it's hard to see the structure of the
   whole thing and relations with other specs.

   nigel: I hate it when clicking on references takes you to the
   Reference section not the thing being referenced.

   Cyril: +1 What's the point in it?

   nigel: What about making defined terms links to other places
   where they're used?

   Cyril: +1
   ... A way to list normative (testable) statements in the spec,
   to generate test suites automatically would be great. CSS has
   that I think.

   tidoust: It was the packaging spec format.

   glenn: That was done by adding markup to every paragraph.
   Extracting assertions from a spec is a hard to automate,
   complex process. Maintaining it becomes quite challenging.
   ... Plus it's not a science. Declarative statements (X is Y)
   can be viewed as normative in some places, then if (X is
   required) implies (Y is required). It's a nice idea, but hard
   to do.
   ... People offer paid services to do that, because it's
   complex.

   nigel: Is there anything else we should know/consider?
   ... Cyril mentioned Developer view/Author view earlier.

   <tidoust> [FWIW, I was referring to the fact that the Packaged
   Web Apps (Widgets) spec was written in a way that allowed the
   extraction of test assertions, see:
   [39]http://www.w3.org/TR/widgets/ and the test suite:
   [40]http://dev.w3.org/2006/waf/widgets/test-suite/#user-agent ]

     [39] http://www.w3.org/TR/widgets/

     [40] http://dev.w3.org/2006/waf/widgets/test-suite/#user-agent


   Cyril: I think there's an HTML 5 spec (might be the WhatWG
   spec) that does differing views.

   glenn: There's a lot of advantage to marking up specs to allow
   automatic extraction. For example, IDL fragments have
   conventions that allow some tools to automatically pull out all
   the IDL
   ... to generate a test generation process. We don't have APIs
   in TTML at the moment. If CSS had followed a similar convention
   for how properties were defined, and HTML had
   ... followed conventions for how elements and attributes were
   defined, then a similar tool could have been used. They didn't
   adopt a convention though, so it's a manual task.
   ... Those are the kinds of tools that it might be useful to
   consider. We could mark up elements and attributes. In the
   original markup I used a few syntactic conventions to assist.
   ... For example ID attributes. I use some specific conventions
   for how identifiers are presented.
   ... I have never documented it anywhere?

TTML2 Timing relationship with related media objects.

   glenn: I can walk us through this. The issue originally came up
   from an example TTML document with some negative time
   expressions.
   ... I immediately pointed out that you can't do that! I did
   wonder why they are putting -ve time expressions in a TTML
   document.

   courtney: Caption authors may use different timecode from the
   video editors.

   glenn: Based on that I thought it would be useful to have an
   offset from authored time expressions to some useful point in
   the media, and allow the player or processor
   ... to use that offset to achieve synchronisation rather than
   mandating precise synchronisation between TTML times and the
   media times.
   ... As I explored that some issues came up. One was the
   difference between the Origin of the document timeline and the
   Begin of the document timeline, and whether they
   ... are different times or the same time. I looked at SMIL and
   SVG time semantics to try to ascertain what was used there. I
   also reviewed the earlier TTML1 work.
   ... We have a concept in TTML that has its own terminology
   definition in TTML2, Root temporal extent.
   ... When this talks about beginning or ending, does it mean
   beginning of the coordinate space or the first timestamp in the
   document.
   ... Say a TTML document has a body with begin="10:00:00". Is
   the origin "10:00:00" or 0s in the document. I eventually
   tentatively concluded that for document time coordinate
   ... spaces is always zero and the beginning of the document is
   always zero. That doesn't mean it's the timestamp of the first
   timed element in the document.
   ... Everything in SVG and SMIL is predicated on the default
   begin being zero, in the coordinate space of the document.
   Recently I came round to understanding that the document
   ... time origin and the document begin point in time are the
   same. Then if I want to synchronise a document with some media,
   then what point am I synchronising? The origin of the
   ... media timeline or the begin. Let's say for example, I have
   a related media object that starts at 5 hours into the media
   timeline. The first timestamp in the media is 5:00:00 (5
   hours).
   ... What do I want to synchronise the 10 hour time in the
   document with, in the media? There are 2 options. One is to
   have zero in the document time coordinate space correspond to
   ... zero in the media time coordinate space. Another is to say
   that there's an offset between the document time coordinate
   space and the media time coordinate space, and that offset
   ... is between the two origins of the coordinate spaces. A 3rd
   option is to pin the origin of the document coordinate space
   (zero) to the begin of the media time coordinate space (5
   hours).
   ... That latter one doesn't seem to be quite so correct.
   ... [draws a picture]

   nigel: Is this predicated on timebase="media"?

   glenn: Let's assume that. The general answer may extend to
   continuous SMPTE timebase too.
   ... I have two entities, a video and a document. Each has a
   timeline - the video content has a timeline and the document
   body has a timeline.
   ... The root temporal extent of the document is the timed
   beginning of the document to the timed ending of the document.
   The choices seem to be the origin or the start of the
   ... first timed element.
   ... I think the logical begin is always zero, if begin is not
   specified.
   ... So this is the document time reference synchronisation
   point. What do want to tie it to - the beginning of the media
   or the origin of the video time coordinate space?
   ... My thinking has evolved on this. Originally I thought that
   Begin(body) would be synchronised with Begin(media). Then the
   offset would be between those two points.
   ... The more I thought about it the less viable it seemed to
   be. Eventually I came to the conclusion that we should
   synchronise Origin(document) and Origin(media).
   ... Then if they happen to correspond, and both the video and
   the body say 10h in their own coordinate spaces then they would
   line up.
   ... i.e. they would be isomorphic time spaces with zero offset.
   ... One of the interesting example issues is: what if the
   playback rates differ between the media and the document. What
   happens to dilations or contractions in the timelines?
   ... It seems like if they're both synchronised with the zero
   point then any modification of the playback speed, as long as
   they're coordinated, would work out pretty well.
   ... It means that you can simply multiply the coordinates with
   the playback rate.

   <Cyril> scribeNick: Cyril

   nigel: (describing an email sent earlier)
   ... I analyzed it a different way
   ... with all possible combinations of timebase and related
   media
   ... 3 different timebases in TTML: media; SMPTE; and clock
   ... what "relationship" means in the temporal extent definition
   ... if there is no related media, there is no relationship,
   that's easy
   ... the root temporal extent is from begin to end of document
   ... they can be unconstrained
   ... begin is origin and end is infinity
   ... if clock time is used, there might be a relationship with
   some media
   ... nothing here contradicts Glenn
   ... example: tape with every frame with timecode
   ... if you are using media times, the origin of the document is
   the begin of the media
   ... you expect the origin of hte document to be equivalent to
   the begin of the media
   ... 5s in the document means 5s in the media
   ... the root temporal extent is constrained by begin media/end
   media

   glenn: SMIL and SVG make the difference between the specified
   and active time interval
   ... the question: is root temporal extent meant to express the
   active interval or the extent of the time coordinate space of
   the document ?

   nigel: the next limitation is when you have media with SMPTE
   timecode and SMPTE timecode in the document
   ... the document times and media times are actually the same
   ... so no offset applies here
   ... for marker mode = continuous, this is equivalent to saying
   origin(document)=origin(media)
   ... however the rule as stated also works for marker mode =
   discontinuous
   ... i.e. when document times = media times
   ... next: media with SMPTE time codes and clock in the document
   ... the only interpretation is that the document types are
   supposed to be equivalent to clock times when you play the
   media
   ... ex: document time says 10:05, but starts playing at 10:03
   ... the use case for this are strange

   glenn: wall clock values are converted to times by substracting
   the wall clock start time of the document (according to SMIL)

   nigel: consistent with my interpretation ?

   glenn: yes

   nigel: then there is a category of media with no SMPTE time
   codes, but with time
   ... same as glenn, the origin of the document is equivalent to
   the origin of the media
   ... again the framing that glenn talked about applies
   ... the active time cannot go outside of the playback

   glenn: the media active interval is as if it was a parent of
   the document active interval

   nigel: if audio is continuing but video is not, the viewer is
   continuing, you should be presenting subtitles
   ... this is an implementation case
   ... any offset that needs to be applied will be externally
   ... I don't want to duplicate what is already in MP4 files for
   instance

   glenn: the timeoffset I came up with makes it easier
   ... if the house that made the media did not have the media in
   hand, they can provide the offset

   nigel: is that a hypothetical case ?

   courtney: no
   ... different houses will have different conventions
   ... when someone give content to itunes, they give a video
   ... later on they'll get european or asian conventions

   nigel: i don't understand the convention

   courtney: some times people don't want to use zero

   nigel: in SMPTE time code yes

   <nigel> scribeNick: nigel

   Cyril: I understand Courtney's use case. The TTML document
   doesn't reference the media itself. So it will be used in some
   external context with the media.
   ... For example an MP4 file, MSE, DASH. All of those have
   timestamp offset facilities, so I'm puzzled why we're talking
   about this here.

   glenn: Those are all different systems with different ways to
   express the offsets. If it only can be carried outside the
   document it might get lost.
   ... It's useful to have it in the document as a reference point
   to express the intent of the author. We often need to export
   things from in the document to outside the document.

   Cyril: So you want to export from the document some time
   reference?

   glenn: yes

   Cyril: That is fine.

   glenn: Courtney isn't the only person to bring this up - I've
   had other reasons to add this over the years.

   courtney: complex production workflows do mean that we
   sometimes need to do this.

   Cyril: These examples seem to be overly complicated.

   glenn: I think nigel wanted to cover all the cases, which is a
   useful exercise.
   ... Neither of us defined BEGIN(document) and ORIGIN(document)
   actually meant, which is a problem talking about this!

   <Cyril> glenn:

   glenn: Is it the time of the first thing in the time frame or
   the origin of the framing time.

   nigel: the next row is where the media doesn't have timecode
   but the document has smpte timecode, which may start at some
   arbitrary point according to convention.
   ... In that case I can see that an offset would be useful, to
   say "the start of the media is at e.g. 10:00:00". I'm less
   comfortable doing this with media timebase, but it's quite
   closely related.

   Cyril: The same problem will arise with WebVTT.
   ... The general problem is how to carry in-band the time value
   of the begin of the media in the document timeline.

   nigel: Do houses really begin at 300s?

   courtney: I only see this as a real world problem with TTML,
   not WebVTT.

   glenn: I've seen examples with media timeBase. For example,
   taking into account a pre-roll of 13s.

   courtney: This could also apply to WebVTT at some point in the
   future.

   glenn: I added a few notes. I need 2 questions answered.
   ... My hypothesis is that the label BEGIN(document) means the
   origin of the document, i.e. zero on the document time
   coordinate space.
   ... I believe that's most accurate in relation to SMIL and SVG.
   ... This is not the time of the body.
   ... Now the question is what we call the Root Temporal Interval
   - does it also start at the origin, or at the body. We may need
   to distinguish the active root temporal interval
   ... from the overall unqualified root temporal interval.
   ... I want to see if the group can agree that hypothesis.
   ... Then I need a decision on which of the 3 models to use to
   describe the timing relationships.
   ... 1) The two origins sync up.

   courtney: I don't see how that solves it.

   Cyril: That's the only one that works!

   nigel: +1

   glenn: In that case the offset is the difference between the
   origins.
   ... 2) The origin of the document syncs up with the beginning
   of the media.
   ... This one seems more natural to me because 10 hours means 10
   hours into the video.

   nigel: Not if the timebase is smpte! You have to enumerate all
   the options.

   glenn: 3) Begin(body) is begin(media). I don't think this one
   works too well.
   ... When you use media times instead of timestamps then you
   mainly want 2). But with SMPTE timecodes in the media it seems
   like 1) may be more applicable.

   nigel: I think that's right.

   Cyril: There's another way to do this - what happens if you
   have an audio track with some offset too?
   ... In the MP4 and DASH case, and all the others I know, you
   only care about the media itself. The TTML document has an
   anchor point, e.g. 10 hours if that's the begin of the media.
   ... Then you use that to anchor it onto the timeline. In MP4 if
   the video has a big gap at the beginning, you use an offset to
   say when the beginning should occur. Same with the audio.
   ... The TTML document should just give its anchor point as the
   time value in its coordinate space that corresponds to the
   beginning of itself.

   nigel: +1 that's the proposal I made too.

   glenn: So you're saying a media begin point as opposed to an
   offset in the document timeline?

   nigel: yes.

   glenn: So if zero in the document is zero in the media the
   media offset is 0
   ... And for SMPTE timecode with the 10:00:00 convention the
   value would be 10:00:00.
   ... I like that suggestion because it seems to work regardless
   of the timeBase. Have you worked through any play rate
   differences?

   nigel: I'm not confident that I've worked through all the
   playrate consequences.

   Cyril: The solution seems to be found - it needs to be liaised
   back to MPEG because it affects the carriage of TTML in MP4.
   You'd have to store it in the MP4 file.

   glenn: Couldn't you just look in the TTML document?

   Cyril: Let's say your document has an offset of 10 hours - will
   the first sample say 10 hours or zero - is an edit list
   required?

   glenn: In SMIL you can have captions that start before the
   media and end after, but get effectively truncated. Why would
   it affect the carriage in MP4? You can still look inside the
   document.

   Cyril: When you stream/seek/segment the document you don't want
   to look inside it.

   glenn: I think I have enough guidance on this to move forward
   on resolving it.

   nigel: Let's take a break - back at 11.

IMSC 1 CR Exit criteria

   action-345?

   <trackbot> action-345 -- Nigel Megitt to Make request to philip
   and silvia to change living standard to editor's draft. -- due
   2014-11-03 -- PENDINGREVIEW

   <trackbot>
   [41]http://www.w3.org/AudioVideo/TT/tracker/actions/345


     [41] http://www.w3.org/AudioVideo/TT/tracker/actions/345


   close action-345

   <trackbot> Closed action-345.

   nigel: sorry that was the wrong action but it was done!

   action-346?

   <trackbot> action-346 -- Nigel Megitt to Scribe notes on cr
   exit criteria for imsc 1 based on meeting debate -- due
   2014-11-03 -- PENDINGREVIEW

   <trackbot>
   [42]http://www.w3.org/AudioVideo/TT/tracker/actions/346


     [42] http://www.w3.org/AudioVideo/TT/tracker/actions/346


   close action-346

   <trackbot> Closed action-346.

   nigel: Goes through scribed notes - group makes edits
   ... Conclusion is:

   Our criteria for exiting CR will be:

   Provide an implementation report describing at least 2
   independent implementations for every feature of IMSC 1 not
   already present in TTML1, based on implementer-provided test
   results for tests and sample content provided by this group.

   We will not require that implementations are publicly available
   but encourage them to be so.

   We will not exit CR before January 16th 2016 at the earliest.

   pal: That's enough for me to edit the SOTD in the CR draft -
   I'll need to get respec.js to allow this custom paragraph.
   ... The next CR draft may include this text in a weird style
   just to get around respec.js.

   nigel adjourns meeting for lunch - restart at 1300

   /|

   group reconvenes

Change Proposals

   Reviewing change proposals at
   [43]https://www.w3.org/wiki/TTML/ChangeProposalIndex


     [43] https://www.w3.org/wiki/TTML/ChangeProposalIndex


   Change Proposal 15

   [44]https://www.w3.org/wiki/TTML/changeProposal015


     [44] https://www.w3.org/wiki/TTML/changeProposal015


   glenn: margin - this would be very easy to add since there's a
   straight mapping to CSS. I haven't had enough feedback that its
   needed.

   nigel: There's nothing from EBU

   courtney: margin isn't permitted in WebVTT either.

   glenn: The described use case, for indenting 2nd and subsequent
   lines, wouldn't be supported by margin anyway. It's really a
   hanging indent.
   ... We don't have any indent support, hanging or otherwise.

   nigel: Is there a related issue for margin?

   glenn: I don't think so.
   ... I'll edit this on the fly now.
   ... marked as WONTFIX.
   ... box-decoration-break. This got moved in CSS to
   'fragmentation'

   <glenn> [45]http://dev.w3.org/csswg/css-break/


     [45] http://dev.w3.org/csswg/css-break/


   <glenn> [46]http://www.w3.org/TR/css3-break/


     [46] http://www.w3.org/TR/css3-break/


   glenn: but the short name is still css-break! It was last
   published as a WD in TR on January 16.

   <glenn> [47]http://www.w3.org/TR/2012/WD-css3-break-20120823/


     [47] http://www.w3.org/TR/2012/WD-css3-break-20120823/


   glenn: Mozilla seems to have an implementation of this that's
   working.

   nigel: Even in today's draft the property and value combination
   still exist.

   glenn: We have two options in TTML2 syntax: either use
   box-decoration-break directly or go ahead and use something
   simpler like linePadding and map it to this CSS property.
   ... The latter disconnects it as a feature from this particular
   instantion.

   nigel: That's the normal way we do it, but I can see that with
   padding specified on content elements then it would be a
   duplication to add it a second time through linePadding.

   glenn: In that case I proposed adding support for
   box-decoration-break in addition to padding on inline content
   elements that can now be specified.

   PROPOSAL: support the EBU line padding proposal with the
   combination of padding on inline content elements and
   box-decoration-break.

   RESOLUTION: We will support the EBU line padding proposal with
   the combination of padding on inline content elements and
   box-decoration-break.

   issue-286: (TTWG F2F today) We will support the EBU line
   padding proposal with the combination of padding on inline
   content elements and box-decoration-break.

   <trackbot> Notes added to issue-286 Extend the background area
   behind rendered text to improve readability.

   glenn: border - we've added border and made it applicable to
   both region and certain content elements - body, div, p and
   span.
   ... One of the open questions is that border in css is a short
   hand for specifying the width height and colour of all the
   borders simultaneously, not each border separately.
   ... As well as this super-shorthand border property, there is
   the border-width, border-style and border-color properties,
   which allow those values to be specified on all or any from 1-4
   borders separately.
   ... Then finally there are 12 long hand versions for each of
   these plus -top -right -bottom and -left.
   ... I've implemented the shorthand, but we could go for the
   more longhand versions.

   nigel: We should check what's needed to match 708 window
   styles.

   courtney: The FCC regulations don't go to the level of
   granularity of this.

   glenn: I think this note came up when we were doing SDP-US -
   there has been a request in the past to describe which 708
   features are supported in TTML.

   courtney: That's not the same as a requirement. I don't know of
   any examples of subtitles with borders on them.
   ... 708 says borders may be raised, depressed, uniform or
   drop-shadow.
   ... I don't see anything about styling the different sides
   separately.

   glenn: It's not clear what the mapping is for all those values.
   box-shadow in CSS may apply where drop-shadow is required in
   708.
   ... They also introduced border-radius.

   nigel: Let's move on from this - I think we've done enough.

   glenn: line stacking strategy. I don't think we need to do
   anything on this right now - I put this in originally, so I'll
   mark it as under review by me.
   ... region anchor points - this was a proposal from Sean to
   have an auto keyword for the origin and extent properties on
   regions.
   ... I believe there's something like this in WebVTT.
   ... TTML doesn't have these at the moment. Sean was the
   champion and we don't have any other champion or requirement
   for this right now.
   ... I would say we should not take any action on this right
   now.

   nigel: I agree - it's unclear even how the proposal maps to the
   WebVTT way of positioning and sizing regions.

   glenn: text outline vs text shadow. When we defined textOutline
   in TTML1 CSS was also working on an outline property.
   ... the new CSS definition of drop shadow allows you to specify
   multiple shadows simultaneously.

   courtney: the FCC regulation requires text edge attributes:
   normal, raised, depressed, uniform and drop-shadow.

   glenn: TTML1's textOutline offers thickness and blur radius.
   You'd have to have multiple simultaneous shadows to achieve
   raised and depressed styles.

   courtney: Authoring that would be complex.

   glenn: XSL-FO defined a text shadow property even though CSS
   had not done so. We ended up calling it textOutline and we also
   limited it to just one dimension, not two.
   ... It's now officially defined in the CSS 3 text decoration
   module, called text-shadow. It takes 2 or 3 length
   specifications.

   <glenn>
   [48]http://dev.w3.org/csswg/css-text-decor-3/#text-shadow-prope

   rty

     [48] http://dev.w3.org/csswg/css-text-decor-3/#text-shadow-property


   glenn: What we could do is define some new keywords that the
   processor can map. That makes it easier for the author to
   choose amongst the different choices including raised and
   depressed.

   courtney: That seems like a nicer way to do it.

   nigel: +1

   glenn: There are two questions: firstly, should we change the
   name from textOutline to textShadow? I would say no. We can
   just define the mapping semantics, and already have different
   naming anyway.

   Proposal: retain the attibute name textOutline.

   glenn: Proposal: add two new keywords for raised and depressed
   to meet FCC requirements and define mappings.
   ... There's a third proposal to add a 3rd optional length
   specification. This would allow separate definition of offset
   in x and y as well as blur.
   ... I see that textOutline doesn't offer a shadow, but a
   uniform outline that expands by the required length around the
   glyph.
   ... I need to think about this some more.
   ... Now I recall why we thought about adding a new attribute
   called textShadow, to allow this. I don't want to take away
   textOutline and remove backwards compatibility.
   ... either we enlarge the definition of textOutline to make it
   include shadow, or add a new textShadow property. I need to
   review it and see if I can come up with a proposal that works.

   nigel: We're getting behind on the agenda. We'll come back to
   this later.

Change Proposal 25 - Distribution

   [49]https://www.w3.org/wiki/TTML/changeProposal025


     [49] https://www.w3.org/wiki/TTML/changeProposal025


   <scribe> scribeNick: courtney

   : nigel: tab to autocomplete is great!

   nigel: : topic is combining groups of documents

   cyril: in the tool mp4box, if you import ttml files to mp4 and
   concatenate more than one ttml file, then extracting the track
   should give you a combined ttml document.

   glenn: xml:id uniqueness- a similar problem exists in ISD
   creation as described in the document combining proposal.
   ... btw, do you have an example of a specification for a merge
   algorithm? an xml syntax?

   nigel: rules are laid out in presentation

   glenn: so you wouldn't have some way for documents to specify a
   set of rules that it can follow?

   nigel: no, there would be an external set of rules

   glenn: would there be any content support required- additional
   metadata, etc?

   nigel: no

   glenn: you could exclude documents that contain elements with
   mixed content

   nigel: perhaps, but that might be difficult because you could
   not use break spans within a sample.

   <courtney_> nigel: normalize whitespace for comparison of
   samples.

   <courtney_> nigel: to compare elements, need to transform their
   times into a common timeline.

   <courtney_> glenn: you could translate to the isd space first
   prior to comparison.

   <courtney_> nigel: not sure what is possible with that
   approach.

   <courtney_> glenn: this is a transformation process, could be a
   separate spec from TTML.

   <glenn> ACTION: glenn to check if timeContainer explicitly has
   no semantics with timeBase smpte, markerMode discontinuous
   [recorded in
   [50]http://www.w3.org/2014/10/27-tt-minutes.html#action05]

   <trackbot> Created ACTION-347 - Check if timecontainer
   explicitly has no semantics with timebase smpte, markermode
   discontinuous [on Glenn Adams - due 2014-11-04].

   <courtney_> glenn: does the ttp:documentGroup type <xsd:NCName>
   proposal match the syntax of Id in XML?

   <courtney_> glenn: yes it does match

   <courtney_> what's the motivating use case for this?

   <courtney_> nigel: to archive live created subtitles documents
   and to be able to create distributable time constrained
   segmented documents for streaming

   <courtney_> Cyril: I'm not convinced there is a need for
   standardization here yet.

   <courtney_> pal: is there a need for a standard when dealing
   with a private archive where the owner controls what goes in
   and what comes out?

   <courtney_> courtney_: ttml requires lots of small files for
   captioning live events, and this seems like a limitation to me

   <courtney_> pal: no it doesn't have to be, streaming inherently
   involves lots of files

ISD formalisation

   <nigel> scribeNick: nigel

   glenn: shows a terminal window! Invokes some code (ttx.jar)
   with a command line specifying the external-duration and an
   input ttml file
   ... Looks at TTML input document, that would present as 0-1s:
   Foo, 1-2s: Bar, 2s-[unbounded]: Baz
   ... Code validates the input and then writes out 3 Intermediate
   Synchronic Documents (ISDs).
   ... looks at output documents. isd elements in new isd
   namespace, with begin and end on the top level element.

   group questions status of this work.

   glenn: TTML1 defines ISDs but no serialisation of them, nor are
   all semantics fully defined. In TTML2 ED there's an annex that
   defines these, with a syntax for ISD.
   ... This is a proposal with the option for change.

   pal: If we say any TTML document can be split unto a number of
   ISDs why isn't each ISD itself a TTML document. Why introduce a
   new structure?

   glenn: Some good reasons. One: the constraints are different in
   an ISD document than in a TTML document. For example region
   elements have a body child.

   nigel: You could create the ISDs as individual TTML documents
   prior to rehoming the body to each region and resolving the
   styles, as another option.

   glenn: I explicitly wanted to put the ISD into a different
   namespace to reduce confusion. I realised when I started to
   formalise this then if I started with tt:tt and made it
   ... polymorphic then it would be much harder for people to
   understand, and parsers.

   pal: +1 for that
   ... More fundamentally, can the ISD format be mapped into a
   TTML document?

   glenn: I don't know - that wasn't in my thought process.
   ... There are two reasons for doing this work. One is to create
   HTML versions - you have to convert into a time-flattened
   version of the original TTML and apply the styles, and resolve
   region references.
   ... I wanted to make sure that process was fully articulated,
   which is essential to move forward.
   ... The other strong reason is to make it easily mappable into
   the cue structure of HTML text track. My model for each of
   these ISDs is one cue.
   ... Microsoft in the past tried to put a TTML1 document into a
   cue. It wasn't standardised anywhere. I want to have a good
   story for generic mapping TTML into a sequence of cues
   ... that fit into the TextTrack model. So my motivation was
   that each ISD should be representable as a cue, and furthermore
   to be distributable as a sequence of ISDs.

   pal: How can I turn this back into a TT document?

   glenn: I don't know - I didn't want to do that.

   pal: So you've effectively created a new format.

   glenn: It was my intention to make this a new format that could
   be used for distribution.
   ... The other option would be to heavily profile TTML to allow
   it to be distributable. By the way, there are already more than
   one kinds of document that are specified by TTML.
   ... My proposal would be to use the same MIME type and a
   different document type within that.

   pal: My initial feedback is this introduces a new format in a
   world that has too many already!

   nigel: There are multiple steps here. The first is to formalise
   something that's only conceptual for describing an algorithm in
   TTML1; the second is to make it a serialisable format.
   ... If your end goal is a TextTrack cue why not go all the way?

   pal: My feedback is that we should store these as TTML
   documents.

   glenn: Not only has timing been flattened in this process but
   also styles. The only styles that are expressed here are those
   that are not the initial values.
   ... [shows ISD output] There's an attribute and element called
   "css" meaning computed style set. Coding wise, this has been an
   important step for validating our algorithm.
   ... Notice that it still uses the TTML namespace - it copies
   the body into the region element; there can be more than one
   region in the isd.

   group expresses some reservations about defining a new format

   glenn: There are some questions: 1. Is it important and useful
   to define a serialisation format for ISD?
   ... I think it's both. It would help in many ways and reduce
   the discussion about streamability.

   Cyril: It's not TTML anymore, so it's not streaming TTML. It's
   streaming something else.

   nigel: We have a wider environment in which organisations are
   creating and distributing TTML documents and writing players.
   There's no problem splitting temporally on the client side,
   ... so creating a new format where the temporal division
   happens server side doesn't seem to be necessary.

   group adjourns for a break

   back at 1600

Multimodal Interaction - Debbie Dahl

   nigel: Introduces Debbie as an Observer who has some
   requirements for multimodal interaction and thought the
   solution space may involve TTML.

   ddahl: Introduces EMMA 1.0

   [51]http://www.w3.org/TR/emma/


     [51] http://www.w3.org/TR/emma/


   ddahl: Emma represents captured user input in different
   formats.
   ... Now considering capturing system output as well as user
   input. It's helpful to have inputs and outputs in the same
   format for processing, debugging and analytics.
   ... Could be static, defined ahead of time
   ... Generated dynamically by an intelligent system
   ... EMMA is an XML language. We're thinking about capturing
   output. [shows an example]
   ... This example happens to have an ssml message in it, the
   <speak> element. SSML has lots of available complexity, not
   used in this example.
   ... Then other multimedia things might go along with it, such
   as HTML and other kinds of multimedia output - SVG, whatever
   seems appropriate to the application.
   ... My original question was: if we want to speech synthesise
   some output or synchronise pre-recorded audio with some other
   kind of multimedia, e.g. video, an animation of
   ... planes going across a map etc.
   ... How could we take advantage of the work done in TTML to
   make life easier for us in multimodal interaction to
   synchronise multimedia outputs generated in real time by
   interactive systems.

   pal: If what's generated is audiovisual, that's a possibility.
   ... maybe you want to provide captions.

   courtney: there could be a series of responses with timings.

   ddahl: You could say "There are flights to Boston from
   Denver..." and then ask a follow-up question. When you ask what
   time of day would you be interested in flying, at that point
   ... maybe you display a form.

   courtney: If you had some animation that shows a map, and you
   know it will play for 3 seconds, and then in 3 seconds post
   your next question?

   ddahl: Yes. Would it be as simple as incorporating TTML maybe
   wrapped around another element.

   nigel: Thinking about the concepts in TTML, there's a timeline
   against which things could be synchronised, plus styled and
   positioned text. There is an issue raised for associating
   ... audio representations of text, but at present the spec
   describes visual rendering only.
   ... It could be that SMIL is a good place to go.

   pal: It's certainly more flexible.
   ... Is this purely semantic or is there a playback requirement?

   ddahl: In the vision, there's a system that renders the
   captured input into something human-understandable. In the end
   there would be playback.

   pal: The more you're interested in playback the closer you are
   to TTML or WebVTT which are intended to be used for playback.

   courtney: If you're synchronising other kinds of media it's a
   good choice.

   ddahl: I guess you could use TTML and SMIL?

   glenn: That's right - TTML is designed to be referenced by the
   <text> element in SMIL. In the abstract for TTML we say:
   ... "In addition to being used for interchange among legacy
   distribution content formats, TTML Content may be used directly
   as a distribution format, providing, for example, a standard
   content format to reference from a <track> element in an HTML5
   document, or a <text> or <textstream> media element in a [SMIL
   3.0] document. "

   pal: If you'd like to display text or captions over audio or
   video you should use TTML.

   nigel: If you want to display any text that changes over time
   then TTML is a good fit. Probably the time modes in TTML are
   rich enough to support any use case you're likely to have.

   <Cyril> scribeNick: Cyril

   glenn: you can refer to TTML1 today, because TTML1 is REC
   ... if you need features of TTML2, you'd have to wait

   ddahl: we've done work on what we call "output timestamps", for
   when it is planned vs. when it happened
   ... when it actually happens is easier

   glenn: TTML does not care about when it happens
   ... we say when we want it to happen
   ... we use presentation time stamp in the MPEG sense
   ... however we have one mode where we use the SMPTE time base
   ... using SMPTE Time Code along with the video
   ... you can think of them as labels
   ... when one of these labels in the video appear that is when
   the matching TTML element is active

   (glenn explaining the different modes SMPTE, Timestamps and
   clocks)

   scribe: they derive from SMIL
   ... we use a subset of SMIL, not repeat for instance

   ddahl: we might want to do somethings that does not have to do
   anything at all with text, like picture and music

   glenn: we plan to add support for images and possibly audio in
   TTML 2
   ... we will definitely not support video in TTML

   nigel: the use case for audio is audio description
   ... generally created by the same company

   glenn: we don't want to turn TTML into SMIL light

   nigel: at the moment you have simple SSML
   ... but if you start having details in SSML
   ... this is closer to the processor than the human
   ... I wonder if we couldn't go in that direction in TTML adding
   emotion, pronunciation, ...
   ... like a format called PLS (Pronunciation Lexicon
   Specification)
   ... this wouldn't affect the TTML document structure at all
   ... that could guide synthetise audio
   ... There is also EmotionML that is interesting
   ... a big use of TTML is for caption and subtitles
   ... but they are just text, without expression
   ... EmotionML gives you some information
   ... but how do you present that emotion

   glenn: like emoji

   courtney: there are conventions also
   ... describing the way the text was spoken (not the emotion)
   ... that's an interesting idea to explore
   ... the most artful captions have seen describe the way the
   text was prononced

   ddahl: emotionML has different vocabularies
   ... there is a standard vocabulary, but you can add your own

   courtney: if you would be too heavy handed in the way you
   describe the emotion, it could be condescending to the hard of
   hearing
   ... you'd have to do it artfully

   ddahl: some people may have a processor to process emotionML

   nigel: currently the emotions are in the text, forcing everyone
   to view them
   ... if you capture emotion and pronunciation would suffice to
   synthesize speech

   ddahl: you would need prosody or other aspects

   nigel: no one has brought this use case to TTML first

   <nigel> [52]http://www.w3.org/TR/emotionml/


     [52] http://www.w3.org/TR/emotionml/


   ddahl: I had an example of annotating a video with EmotionML

   glenn: TTML allows you to mix any content if it is in a
   different namespace

   Cyril: Example 2 of annotation of videos in the emotionML spec
   seems to have problems (use of ? instead of #, use of "file:"
   instead of "file:///"

   (ddahl shows a demo)

   nigel: you can either add external content to TTML or extend
   TTML

   Cyril: you might want to consider using a separate track
   ... not merging it in the TTML document but using a separate
   track in the HTML sense

   nigel: there does not seem to be any action on this for us at
   the moment

   ddahl: I came looking for information and i'll bring that back
   to my group

   <nigel> scribeNick: nigel

Change Proposal 14 Audio Rendering

   [53]https://www.w3.org/wiki/TTML/changeProposal014


     [53] https://www.w3.org/wiki/TTML/changeProposal014


   nigel: I was going to propose as per CP14 that we consider
   adding PLS and EmotionML into TTML but it seems that we do not
   need to: foreign namespace content can already
   ... be added with no spec changes.

   issue-10?

   <trackbot> issue-10 -- Allowing pointers to pre-rendered audio
   forms of elements -- open

   <trackbot>
   [54]http://www.w3.org/AudioVideo/TT/tracker/issues/10


     [54] http://www.w3.org/AudioVideo/TT/tracker/issues/10


   Issue 10 proposes adding a pointer to an external audio file,
   which is the analogue to a pre-rendered graphic image.

   nigel: Issue 10 proposes adding a pointer to an external audio
   file, which is the analogue to a pre-rendered graphic image.
   ... CP14 is a Priority 3 on our list, so I don't think we
   should spend any more time on it right now.
   ... Instead, we should go through the Priority 1 CPs and
   resolve any outstanding questions so that we can complete the
   TTML2 deliverable.

   glenn: Let's return to CP15. We were up to shrink fit
   ... We don't have a champion for shrink fit and no issue, so I
   propose to do nothing.
   ... font face rule - we do have an issue for that. I'm not sure
   if we need the fontFaceFormat attribute.
   ... This implies that there's a fallback loading system that
   would pick the source that it knows how to process.
   ... That would introduce something new in TTML2, which is the
   ability to refer to resources outside the document.
   ... There's a way to get around it, which is to use data URL,
   i.e. embed the data as BASE64 encoded characters in the
   document.

   nigel: I prefer external references for fonts because they
   allow caching.

   glenn: There's a similar issue for backgroundImage resources.
   ... I don't have any open issues on this one.
   ... multiple row alignment
   ... I haven't worked through the possibility of using flexbox.
   I tried to generate some samples and they seemed to produce the
   same results.
   ... I don't want to introduce all of flexbox into TTML2. My
   current thinking is to define a TTML-specific property given
   the semantics according to the proposal.
   ... As part of the mapping to HTML it could potentially be
   mapped to flexbox.
   ... So I need to define a new property that is named
   appropriately and provides these semantics.

   nigel: How will we reference the pre-existing similar feature
   in IMSC 1 and EBU-TT?

   glenn: I don't mind drawing attention to this with a Note if
   people think that's useful - it's just editorial work.
   ... Superscript and subscript: I think I've already closed
   that.
   ... Ths issue is closed.

   nigel: marks it as closed on the CP.

   glenn: Change Proposal 16 - Style conditional
   ... I need to review this. I thought this change proposal had
   to do with an informal proposal I made where I described a
   condition attribute on some elements, where
   ... the value of the condition attribute is an expression in a
   simple expression language, whose evaluation, if false, would
   result in the element being excluded from presentation,
   otherwise
   ... treated as though there were no condition attribute
   present. This came out of the forcedDisplay discussion.
   ... I was going to have a simple expression language that at
   minimum looks like a list of functions in CSS where the names
   of those functions would be drawn from a list of
   ... predefined function list, e.g. "parameter(parameterName)"
   with some defined built-in parameters like "forced" so if you
   want to exclude some content based on this parameter
   ... being false then you would have a
   condition="parameter(forced)=true" that would be evaluated
   during the rendering and presentation process (specifically in
   the ISD generation process).
   ... I need to reread this CP and think about it - the proposal
   seems to have used something more like a media query
   expression. Sean wrote this originally I think.
   ... At minimum I want the condition mechanism to support forced
   semantics. Beyond that I don't have a real agenda.
   ... Other uses might include language.

   nigel: Another is where you may want to preferentially display
   images vs text under some circumstances.

   jdsmith: Are the only conditional inputs for this smooth
   animation and 4:3/16:9 video format? This looks like
   conditional styling.

   glenn: I'm talking about more general conditional expressions
   ... It's an interesting idea to consider feature support
   conditionality.
   ... CP17 Default styles
   ... This is mostly closed. It remains to be defined what a
   pixel means.

   issue-179?

   <trackbot> issue-179 -- Interpreting the pixel measure -- open

   <trackbot>
   [55]http://www.w3.org/AudioVideo/TT/tracker/issues/179


     [55] http://www.w3.org/AudioVideo/TT/tracker/issues/179


   pal: I think most people with CFF and SMPTE-TT think that when
   they author the document the video object has a certain number
   of pixels, and those are the ones they refer to.
   ... They literally relate to the encoded pixels, those in the
   AVC stream for example.

   glenn: Those pixels don't have a size at that point. Then they
   get mapped into a display pixel which does have a size.

   pal: And my 640x480 then gets mapped to a display pixel on my
   1280x720 display.

   glenn: And at that stage the pixel has a concrete size.

   pal: That's my understanding.

   glenn: The rendered pixel is dependent on lots of other
   variables.

   Cyril: But that's not the coded pixel either. In AVC for
   instance you code a pixel, an RGB or YUV value or whatever.
   Then you stretch that according to the pixel aspect ratio.
   ... and then you may apply a clean aperture, to cut out some of
   the image, to make it the right multiple of macroblock size. So
   my guess it that people authoring TTML base it on
   ... the result of this process, taking the output of this
   decoding process, then applying the sample aspect ratio, then
   any cropping.

   glenn: I think this is an open question, it's not necessarily
   like that. For example in SD video you often have 720 pixels
   per line but you only display 704 pixels, so there's an 8 pixel
   buffer on either side
   ... to allow for overruns. So what we were describing is a
   0-719 coordinate space whereas what you were describing was a
   0-713 coordinate space.

   Cyril: Yes, if the video was cropped then you'd have some
   invisible text.

   pal: Some codecs have the ability to store a power of 2 number
   of pixels, internally. Then on the output it has internal
   cropping to put back the right value from the input.
   ... So is it literally the power of 2 internal array or the
   output of the decoder.

   Cyril: Yes, to give an example, in an MP4 file you have 3
   sizes:
   ... 1. The size of the buffer that needs to be allocated.
   ... 2. The result of applying sample aspect ratio and cropping.
   ... 3. Applying a possible scale to the result, usually not
   done.
   ... So in an MP4 file you have the sample entry width and
   height, the clap and pasp width and height, and track header
   width and height.

   pal: That first one you mentioned is what comes out of the
   decoder. That's what I think of when I think of stored pixels.

   glenn: We want to pick one and go with it.

   pal: I'm happy that we're not talking about a display pixel.

   Cyril: I agree it's not the 3rd one. If you really want to use
   that you should use the same metrics to the TTML result.
   ... The only choice is 'output of decoder' or output of sample
   aspect ratio plus cropping.

   pal: I'd take out anything that's dependent on ISO BMFF.

   glenn: +1

   pal: I think people have been using decoder output pixels with
   no further transformation.

   nigel: We need to find what's common across all formats.

   glenn: The source buffer is common.

   pal: I'd use that as a strawman.

   glenn: Previously we said 'pixel as defined in XSL-FO'. But the
   definition there is ambiguous - it can be device dependent or
   what CSS says. CSS says 96 pixels per inch,
   ... but it doesn't say which inch applies. They have some
   angle-based visual model including distance, to compute that.
   It's complicated. I think the CSS people gave up on it and made
   ... it an absolute dimension. They did that because it's what
   most people actually use in implementations. We have a similar
   scenario - most people use a different interpretation
   ... from what's in the spec, for whatever reason.

   pal: Yes, they see a video dimension size and go for that.

   glenn: I think on TTML1 we should add an erratum that defines
   pixel, and then use it normatively in TTML2.

   nigel: What's the proposal?

   glenn: We have a tentative proposal to make pixel a 'stored
   pixel' (pal's term) or 'coded sample' (Cyril's term).

   pal: Let me throw another one in the pot.

   glenn: I like 'coded sample' because it avoids circularity of
   definition.

   nigel: Can I clarify that we're talking about no tts:extent
   being specified on tt:tt?

   glenn: I have to do something different based on whether or not
   there's a related media object.
   ... Otherwise there's another definition.

   nigel: I'm worried that we end up with ambiguity between
   tt:tt@tts:extent and the related media object.

   glenn: That's a different problem, that we also need to deal
   with at the same time.

   nigel: This is exactly the same as the root temporal extent
   problem before - we need to relate the root spatial extent to
   an external display rectangle.

   Cyril: I've checked H264 AVC and HEVC and they both define a
   picture as an array of samples, and they both also define a
   message to carry sample aspect ratio.
   ... So the video may have one shape, and the TTML may define a
   different shape rectangle.

   pal: That's right, it's also something we should talk about.

   Cyril: [draws a picture] Decoder produces something with a
   Width and Height (within the decoder). Then you apply Sample
   Aspect Ratio (also within the decoder).
   ... and then, when you display something you may scale it,
   upsample/crop it etc.

   glenn: The array size is the same before and after applying
   sample aspect ratio?

   Cyril: No, the height is the same but the width may change.
   ... If you author using the W and H, and there's anamorphic
   conversion going on then you may need to apply some positioning
   of the TTML extent onto the video.
   ... The 'coded samples' are the ones before scaling with the
   sample aspect ratio.
   ... I don't know what to call the samples after scaling with
   the sample aspect ratio. 'scaled sample'?

   courtney: I'd call them 'square pixels'

   Cyril: that's not how AVC calls them, though it may make sense.

   pal: As a strawman can we use 'coded sample'?
   ... the anamorphic 'pixels'

   courtney: I think it makes sense to use the coded samples from
   the file because then the video in the file and the dimensions
   of the captions are consistent with one another, using the same
   metrics.

   pal: my proposal is use the term 'coded sample', get feedback
   on that as an errata.

   glenn: I'll probably refer to some MPEG document for the
   definition of 'coded sample'. I'm going to say that a TTML
   pixel is a 'coded sample'.

   Cyril: It would be good to provide examples.

   glenn: one interesting scenario is that tts:extent doesn't
   match the coded sample size of the related video object.
   Another is where they do match.
   ... The third is where there's no tts:extent, but there is a
   new ttp:aspectRatio property.

   pal: IMSC says either do 'matching pixel aspect ratio' or
   'define aspect ratio' but not both.

   Cyril: I think we agree but I want to check: If I take an
   anamorphic video, before capture by the camera an object has a
   particular shape. Then after capture it's 'squished' to be
   thinner.
   ... then after decoding it gets restretched to its original
   shape. And what's stored, from the perspective of the coding
   specification, is the squished shape.
   ... So 'square pixels' is something that depends on your
   perspective.

   courtney: So where it the pixel aspect ratio square?

   Cyril: It's after 'unsquishing'.

   group agrees terminology

   pal: In IMSC 1, I will make a revision based on this erratum.
   It should probably say that the goal is never to have to use
   tts:extent and always create resolution independent subtitles.

   Cyril: Can I check that there's no impact caused by interlaced
   and progressive video?

   glenn: We assume it's been deinterlaced.

   courtney: +1

   nigel: In TTML2 how does this impact on viewport-related widths
   and heights?
   ... Do we need to be concerned about the aspect ratio of the
   related video there too?

   glenn: That's what I'm working on at the moment.

   Cyril: SVG lets you specify a viewbox and relate viewport
   coordinates to that too.

   glenn: I'm not sure if we need that too - maybe.
   ... That's all I need for CP17

   Issue-210?

   <trackbot> Issue-210 -- The values for alpha in rgba() don't
   correspond to CSS3 Color definitions -- open

   <trackbot>
   [56]http://www.w3.org/AudioVideo/TT/tracker/issues/210


     [56] http://www.w3.org/AudioVideo/TT/tracker/issues/210


   glenn: cp17 - we allowed 0-255 alpha values but CSS3 defines a
   0-1 scale. So there's an ambiguity if the value 1 is used.

   courtney: Are the types different? Are the expressions
   differentiable by the decimal point?

   glenn: In CSS3 you don't need the decimal if alpha value is 1.
   So you can't infer anything there.
   ... I think we just define the mapping into CSS, because then
   its well defined.

   nigel: I'd argue it's well defined already but just needs to be
   clarified.

   issue-225?

   <trackbot> issue-225 -- tts:fontSize as percentage of container
   dimensions -- open

   <trackbot>
   [57]http://www.w3.org/AudioVideo/TT/tracker/issues/225


     [57] http://www.w3.org/AudioVideo/TT/tracker/issues/225


   pal: TTML1 doesn't really say what you're supposed to do with
   pixelAspectRatio.

   glenn: That's right - it's used to define authorial intent. It
   doesn't say how that should be applied.
   ... But we may need to reference that in the new verbiage.
   ... I put that in originally because PNG has a chunk that
   allows pixel aspect ratio to be defined.

   pal: I think if we go down the path of coded samples then it
   might be good to make sure that pixelAspectRatio is set.

   nigel: Can we resolve this by removing vmin and vmax?

   pal: +1

   issue-225: (f2f meeting) We agreed to remove vmin and vmax.

   <trackbot> Notes added to issue-225 tts:fontSize as percentage
   of container dimensions.

   nigel: CP25. At a minimum that comes down to adding a
   documentGroup identifier.

   glenn: I'm happy to do that.

   nigel: CP5?

   glenn: There are too many details to discuss that. It involves
   converting to ISD! So I have to define that mapping to satisfy
   that.

Wrap-up

   nigel: Thanks everyone - we've covered a huge amount over two
   days, including:
   ... agreeing to publish WebVTT
   ... the MIME type extension
   ... Reviewing the IMSC 1 review comments and agreeing the CR
   exit criteria
   ... thinking about the feelings of our specs
   ... Considering the relationship between TTML and related video
   objects both spatially and temporally
   ... going through the TTML2 change proposals
   ... and we even had time to think about multimodal interaction!
   ... adjourns meeting

   /|

   s/s||/

   s|/

Summary of Action Items

   [NEW] ACTION: cyril Draft a WG note explaining the differences
   and relationships between the various versions of TTML
   [recorded in
   [58]http://www.w3.org/2014/10/27-tt-minutes.html#action02]
   [NEW] ACTION: glenn to check if timeContainer explicitly has no
   semantics with timeBase smpte, markerMode discontinuous
   [recorded in
   [59]http://www.w3.org/2014/10/27-tt-minutes.html#action05]
   [NEW] ACTION: glenn to update point (1) of section 3.1 in ttml2
   to refer to a new annex that defines new processorProfiles MIME
   type parameter [recorded in
   [60]http://www.w3.org/2014/10/27-tt-minutes.html#action01]
   [NEW] ACTION: nigel Make request to Philip and Silvia to change
   Living Standard to Editor's Draft. [recorded in
   [61]http://www.w3.org/2014/10/27-tt-minutes.html#action03]
   [NEW] ACTION: nigel Scribe notes on CR exit criteria for IMSC 1
   based on meeting debate [recorded in
   [62]http://www.w3.org/2014/10/27-tt-minutes.html#action04]

   [End of minutes]
     __________________________________________________________


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Received on Friday, 21 November 2014 17:15:06 UTC

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