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Re: ISSUE-163 navigating-tracks: Chairs Solicit Change Proposals

From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Date: Thu, 7 Jul 2011 10:03:06 +1000
Message-ID: <CAHp8n2nnGO5-icdG4vg-KGWk4Pzu-GAGbtg5iuhuxGjoLLRQTw@mail.gmail.com>
To: Philip Jägenstedt <philipj@opera.com>
Cc: public-html@w3.org
On Wed, Jul 6, 2011 at 11:50 PM, Philip Jägenstedt <philipj@opera.com> wrote:
> On Wed, 06 Jul 2011 14:56:12 +0200, Silvia Pfeiffer
> <silviapfeiffer1@gmail.com> wrote:
>>>> For WebVTT I am expecting a discussion in the WHATWG, since it's not
>>>> specified in this WG. There is bugs that track this, see
>>>> http://www.w3.org/Bugs/Public/show_bug.cgi?id=12662 .
>>> OK, thanks.
>> Do you also think this approach of putting hierarchies inside cues is
>> simpler than building hierarchical structures through separate cues,
>> or even with separate tracks? Or do you have a nicer way of dealing
>> with DAISY-like requirements?
> There are a few things with
> <http://www.w3.org/WAI/PF/HTML/wiki/Media_Navigation> that I'm not a fan of:
>  * I seems a bit random to me to represent top-level chapters as time
> ranges, but sub-chapters as time cues.
>  * There can be no more than two levels. Not a big deal, but all else equal
> not having this limitation would be better.

No, that's not true. The example at
shows 3 levels and there can be an unlimited number.

>  * New WebVTT markup and somewhat magic transformation to HTML.

Not magical - it follows the way in which the WebVTT mapping is
already defined at
, but only adds one element to create the hierarchy.

> Something that could be trivially parsed by both web browsers and scripts
> would be nicer, IMO. If you consider that a chapter is a range, you can
> build a chapter tree by just looking at which chapters are contained within
> another. Example:
> 00:00:00.000 --> 00:00:10.700
> Title Slide
> 00:00:10.700 --> 00:00:47.600
> Introduction by Naomi Black
> 00:00:47.600 --> 00:07:37.900
> Talk on WebVTT
> 00:00:47.600 --> 00:01:50.100
> Impact of Captions on the Web
> 00:01:50.100 --> 00:03:33.000
> Requirements of a Video text format
> 00:03:33.000 --> 00:04:57.766
> Simple WebVTT file
> 00:04:57.766 --> 00:06:16.666
> Styled WebVTT file
> 00:06:16.666 --> 00:07:37.900
> Internationalized WebVTT file
> From this you could programmatically find the chapter tree.

That is possible and is also something I considered at
. The parsing of this and creation of the hierarchical navigation tree
would need to deal with all kinds of possible markup errors, which is
why I find it not so simple to use by authors.

After today's media accessibility task force call, I've added header
markup to that example, which more explicitly states the hierarchical
level. That may help with some of the parsing and could even
auto-correct some markup errors. It could also be more lax about
overlapping time regions and basically just care about start times.

> It also has the
> benefit that it's possible to use this as a visible track for debugging
> purposes, as all currently active chapters would be visible.

How are you suggesting to make chapter tracks visible? I've got an
experiment at http://www.html5videoguide.net/demos/google_io/3_navigation/
and am finding it hard enough to make one level of navigation visible
in the transport bar (the list on the right would not be a default
rendering). I have no good solutions for making multiple hierarchical
levels visible.

> With some
> script+CSS I suppose it might even be a useful technique in production. The
> only downside that I can see is that it's a bit tricky to author.

Yes, I found the ul/li way of authoring more immediately readable.
Providing a non-hierarchical list of cues and making them hierarchical
just through analysis of time markers is asking for a rather complex
algorithm, which is why I tried to avoid it.

Received on Thursday, 7 July 2011 00:04:04 UTC

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