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Media Teleconference Minutes from 6 April

From: Janina Sajka <janina@rednote.net>
Date: Wed, 6 Apr 2011 19:28:14 -0400
To: HTML Accessibility Task Force <public-html-a11y@w3.org>
Message-ID: <20110406232814.GL2453@sonata.rednote.net>
Minutes from today's HTML-A11Y Task Force Media Subteam teleconference are
provided below in (slightly edited) ASCII text and are available as hypertext



                                                           - DRAFT -


06 Apr 2011

   See also: IRC log


          John_Foliot, Judy, Frank Eric_Carlson, Sean, silvia, mark

          John Foliot



     * Topics
         1. Identify Scribe http://www.w3.org/WAI/PF/HTML/wiki/index.php?title=Scribe_List
         2. Issue-152 Multitrack
   Eric: We're a bit closer.
   ... Frank hasn't dropped his proposal yet, but I believe he is going to.
   ... There's quite a bit we like in Ian's proposal and are expecting some modifications from him based on discussion

   jf: are all these discussions being captured in W3C space?

   Eric: Don't know ...
   ... I agreed to forward things, if they weren't

   Judy: Do we want to specify that the discussion on multitrack be copied to the TF list as well?

   JF: Frank, Sean?

   judy: just to clarify, it could be both html and tf lists

   janina: would prefer it was both lists, it's a critical discussion

   silvia: I promissed to write a summary, apoligize it's not done
   ... Ian's proposal is specified in what
   ... I'd like to discuss it.

   janina: Is it at least referenced in W3C space?

   Silvia: Yes, it's referred in the bug on this issue
   ... We have been granted more time for this issue ...
   ... We still have four fundamentally different proposals on the table

   jf: Judy?

   judy: Just concerned that we use the time of people on this call well

   Silvia: Would like to put the controller approach on the table for discussion
   ... Ian suggests simply using js rather than ml
   ... Wondering about advantages vs disadvantages of this

   Eric: His proposal still associates the elements in ml
   ... It explicitly creates a controller object
   ... Negative aspect--majer negative--that timelines are completely independent
   ... It would be possible to play these at different rates,; but this could be confusing for users and hard for devs to
   ... So, we at Apple aren't so thrilled with that

   Silvia: Can you touch on the good things?

   Eric: Yes, we could make this work more logically
   ... Some aspects of Ian, ours, and Seans, for example slaving to a common clock
   ... We gave this feedback to Ian last week--but it was on the what list, sorry

   Eric: Ian did commit to make this change

   Silvia: I believe he's working on it, but I don't know the status

   jf: Do I understand that Ian's controller approach fits with Sean's approach?

   Eric: One aspect of Sean's proposal, last I looked, was to have a text element associated, and Ian doesn't cover that

   jf: And to position the text content?

   Eric: Yes, we agreed to separate that last week
   ... We agree it needs solving, but it's a separate issue

   jf: Do we address it before last call?

   Silvia: At the moment we can render text anywhere on page manually. We want to improve on that using css selector, and
   Sean created a wiki for this

   Sean: Yes, there are several issues around the api for selecting tracks, but they can be handled independently
   ... There are good things in Ian's proposal

   Eric: It would be easier to solve text rendering apart from Issue-152

   Sean: I don't think Ian's has a clean enough approach on mutually exclusive

   Eric: Agree that requiring inband video tracks to be mutually exclusive doesn't make much sense

   Silvia: Agree
   ... Also don't understand why audio can be multiple, but video is exclusive


   Silvia: I believe we can amalgamate these
   ... Frank, have you looked at Ian's Thoughts?

   Frank: Agree there much merit. Agree we start from it

   jf: Does anyone disagree?


   Eric: We need to ask when we can expect an updated version from Ian
   ... It would be helpful for us to continue from an updated spec that incorporates our ideas

   Silvia: I'm messaging him ...

   JF: Main concern is that we have to keep momentum on this

   Silvia: I have an additional question re controller
   ... Inessence this means defining an abstract timeline apart from each of the component elements
   ... Is that possible? An abstract timeline or do we need to pick one?

   Eric: No problem because that's what will happen in the background anyway. All elements will be driven by the hw clock.
   It's an implementation detail
   ... At least in our implementation

   Frank: Can you say more about time offset zero?

   Eric: Having time 0 correspond to one of the files won't be that hard
   ... From the user's perspective don't think it would make sense to have nothing rendered for awahile

   Silvia: Time 0 is where they all start?

   Eric: It may make sense to specify a start time other than 0.

   janina: What about a use case where the alternative is provided in multiple files?

   Eric: Don't doubt that this is the case, but it isn't hard to build the composite file

   Silvia: Don't think multitrack is the best answer for that
   ... Agree that flattening the individual files into a single file is easier for publication, use, etc

   Mark: We currently store each subtitle, etc., in a separate track

   Silvia: But not segmented in time?

   Mark: No
   ... Each file contains the entire duration

   janina: So, continuing as the devil's advocate, what about extended video descriptions?

   Silvia: Yes, that changes the timeline
   ... It's a different problem, and one of the most complex
   ... Would not to like to solve it in multitrack

   Eric: But segmented files wouldn't solve the problem either, because all others would need to be paused while this one
   continues to play

   Frank: Prefer a simpler approach, offset seems too complex
   ... Agree that linking multiple segmented files into a single file should be done in authoring

authoring the media

   jf: So thinking about sign language ... if the sign language tracks stalls for some reason, it should tell the main to
   pause at some point

   Frank: Yes, we can do that today

   Silvia: Am I understanding that the controller isn't the best idea? That one element should be the primary timeline?

   Frank: Yes

   Silvia: So can't you achieve that in implementation? Just pick the one you want to use?

   jf: My concern there is authoring; Now we have to tell people the first video is primary and may not be correct oftimes

   Eric: Silvia's suggesting that that one timeline could be chosen to use as the master
   ... It's only necessary to expose this to authors if we don't require because of data load problems

   Silvia: If we allow any element to be the master, users might prefer different choices

   Frank: if two elements have different length content, how do we reconcile

   Eric: Propose that the duration of the group is the union of its members
   ... Ian has pointed out that it's sometimes not possible to predict
   ... So should be as in video editor, the longer file extends the shorter

   Silvia: So the longest rules

   Frank: And the use case?

   Eric: A movie with director's comments often go longer

   Mark: There's also different packet lengths between audio and video

   <mark> differentpacket durations

   Eric: So if you enable an element that had been disabled, it may make the composite presentation longer
   ... Also think we should apply this principle for display

   Silvia: How so?
   ... They're already displayed in different areas, no?

   Eric: Maybe, maybe not
   ... I suppose depends on controller and what properties we have there
   ... If we require all elements for some time be loaded before we play,

   Silvia: So an abstract state from all the elements that are active?

   Eric: This was in our feedback to Ian
   ... Restating for Sean who some of us couldn't hear ....
   ... Sean smil has this same issue and adopting the behavior that duration of group can be longer of any element we need
   to decide what happens with elements that have video when play goes beyond the end of video
   ... Suggest rendering nothing
   ... Suspect you wouldn't want last sign gesture to be held

   jf: what does smil do?

   Eric: allows to be specified

   <Sean> good summary

   Silvia: Think going to transparent

   jf: so that box would disappear?

   Eric: Yes

   <Sean> does it still contribute to the overall shape however?

   Eric and Silvia say 'yes'

   Mark: Isn't the usual behavior to freez

   Eric: last frame is held because time stops so you see the image for the last frame

   Silvia: Some display links to other videos

   Mark: And if the track is disabled?

   Eric: Then it disappears from rendering

   Frank: I am concerned whether we're taking on more complexity again

   Eric: How different?

   Frank: If longest element wins, what do you do with a loop event?

   Eric: And how is it simpler in the other case?

   <Sean> Is it always the case then that effectively the longest video is always the master?

   Frank: Because we've defined the master

   Silvia: It's the case for both approaches

   Frank: Don't agree

   Eric: So, if we don't require slaved elements ... if we don't pause the timeline because every sample isn't loaded ...
   ... If we require all must load before we play, then I agree it's the same from the implementation viewpoint

   Mark: Sounds like it's simpler to have one master, whichever is the master

   Eric: Don't agree, but let's consider
   ... What do you do with the longer slave?

   Mark: It lengthens the master
   ... So the master is extended to the longest of any of the active elements ...

   Silvia: Yes, and that's the controller
   ... So we change much data about individual elements when we play a group -- so it makes sense to consider the group as
   the master

   Frank: I'll reconsider the proposal

   jf: Four minute warning ...
   ... Silvia, some work on wiki, yes?

   <silvia> yes

   JF: We'll ask Ian to cc W3C lists

   judy: Would it help to have Silvia's summary list remaining questions/issues?
   ... Can we collect now?

   Eric: Several: What should --- Should all group elements have the same controls?
   ... Loaded ranges?
   ... What should happen when script does a seek on one element
   ... Ditto for other attributes -- What happens?

   <Sean> Should in fact media elements have any means of controlling other than the controller

Summary of Action Items

   [End of minutes]


Janina Sajka,	Phone:	+1.443.300.2200

Chair, Open Accessibility	janina@a11y.org	
Linux Foundation		http://a11y.org

Chair, Protocols & Formats
Web Accessibility Initiative	http://www.w3.org/wai/pf
World Wide Web Consortium (W3C)
Received on Wednesday, 6 April 2011 23:28:52 UTC

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