W3C home > Mailing lists > Public > public-html-a11y@w3.org > March 2011

track events.

From: Sean Hayes <Sean.Hayes@microsoft.com>
Date: Wed, 2 Mar 2011 17:44:08 +0000
To: Janina Sajka <janina@rednote.net>, HTML Accessibility Task Force <public-html-a11y@w3.org>
Message-ID: <8DEFC0D8B72E054E97DC307774FE4B913FA9E0FA@DB3EX14MBXC301.europe.corp.microsoft.com>
New Agenda item for today's call if possible.

I have been attempting to implement the current Text Track API, and in particular the event mechanism and I've run into some issues with the current text which I'd like to discuss today; with a view to possibly raising some bugs on the current text.

My understanding of the current text track api is that initially the text track's list of cues is empty. When the text tracks mode is set to anything other than disabled the track resource is fetched and cues may start to get added to the track.cues list.

So far so good.

The text tracks list of cues is written to by the parser for the resource being loaded, and can be updated dynamically while the track state is loading, but there is seemingly nothing in the spec that prevents the parser from continuing to update and completing after the loaded event has been fired. And in the loading state, if the track is being parsed from interleaved in-band data, then each cue may well not be parsed and entered into the cue list until the video playback reaches a point just before the cue is due to be used. Therefore a TextTrackCueList object can contain an indeterminate number of cues. There is no event to tell when or if this list is complete, or any way for an author to easily detect that new cues have been added.

                Q1: Should the loaded event be delayed until after the text parser has completed?
                Q2: Should there be an event or some other mechanism while in the loading state to detect that the list has changed
                Q3: Should there be an event or some other mechanism to detect that the list is final

An author wishing to detect the entry and exit of cues needs to set event handlers individually on each cue in the list, the EventTarget API gives no means of detecting whether a handler has been set. So it is problematic, given that cues may be arriving in a 'just in time' manner, for an author to be able detect the addition of a cue, know whether it has a handler set on it, and to have time to attach an event handler to it  before the playhead passes its active point.

                Q4: Should the onentry/onexit events be removed from cue; and update the oncuechange event on track to receive a list of incoming and a list of outgoing cues as argument so that a) It is possible to set the handler before any cues are added at all, b) so that only a single handler needs to be set, c) make the 'activeCues' list redundant, and d) clear up where these events would bubble to.


-----Original Message-----
From: public-html-a11y-request@w3.org [mailto:public-html-a11y-request@w3.org] On Behalf Of Janina Sajka
Sent: 02 March 2011 09:03
To: HTML Accessibility Task Force
Subject: Agenda: HTML-A11Y Media Subteam on 2 March at 22:00Z for 90 Minutes

SPECIAL NOTE: Please note the new Zakim facilities announced below. We
will discuss the new SIP option in a forthcoming call.

* Time of day conversions

You can check for the correct time of this meeting in your time zone
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** preliminary agenda for HTML-A11Y Media Subteam Telecon 2 March 2011, 22:00Z (for 90 minutes)

Meeting: HTML-A11Y telecon
Chair:	John_Foliot
agenda: this
agenda+	Identify Scribe
agenda+ Actions Review http://www.w3.org/WAI/PF/HTML/track/actions/open
agenda+ Face to Face--Please Register http://www.w3.org/2002/09/wbs/44061/201103_ftf/
agenda+	Issue-152 Multitrack API http://lists.w3.org/Archives/Public/public-html-a11y/2011Feb/0079.html
agenda+	Bug 10693 - Need a means for navigating between related timed tracks of media elements
agenda+ Poster
agenda+	Other Business?
agenda+ be done

** Resource: Face to Face Registration Page:

** Resource: Previous Teleconference Minutes
Media Subteam:	http://www.w3.org/2011/02/23-html-a11y-minutes.html

** Resource: Key Task Force URIs
Task Force Wiki:	http://www.w3.org/WAI/PF/HTML/wiki/Main_Page
User Requirements: http://www.w3.org/WAI/PF/HTML/wiki/Media_Accessibility_Requirements
Technical Dependencies: http://www.w3.org/WAI/PF/HTML/wiki/index.php?title=Media_Accessibility_Checklist
Consensus Procedures:	http://www.w3.org/WAI/PF/HTML/consensus-procedures
Work Statement:		http://www.w3.org/WAI/PF/html-task-force.html

** conference infrastructure access information a.k.a. dial-in  instructions

Reference: http://www.w3.org/Guide/1998/08/teleconference-calendar.html#s_273

2011-03-02, 22:00Z (for 90 minutes)
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This is

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Janina Sajka,	Phone:	+1.202.595.7777;
Partner, Capital Accessibility LLC	http://CapitalAccessibility.Com

Marketing the Owasys 22C talking screenless cell phone in the U.S. and Canada
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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, 2 March 2011 17:44:45 UTC

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