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RE: Re: questions on simple profile - nested spans

From: Sean Hayes <Sean.Hayes@microsoft.com>
Date: Tue, 7 Aug 2012 18:01:13 +0000
To: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
CC: "Goldstein, Glenn" <glenn.goldstein@viacom.com>, "public-tt@w3.org" <public-tt@w3.org>
Message-ID: <E9A92BD0A4FC934EB7935470A46D1524091752D2@DB3EX14MBXC324.europe.corp.microsoft.com>
The processing happens so that at each time instant T,  the TTML tree is pruned to leave only elements temporally active at time T. Then what remains gets laid out essentially as if it were HTML for each time T; (the actual processing is simplified, because it is possible to compute the set of 'interesting' times at which something changes). At each interesting time T the region is effectively cleared and reflowed.

In the example the timing is arranged on the <p> and <span>s such that each word <span> appears sequentially, and each line <p> is timed to stay visible for 11s. So for example at T=24 the top line has expired, and the remaining markup would look like:

 <p >

  <span >with</span>

  <span >word</span>

  <span  >at</span>

  <span  >a</span>

  <span  >time</span>

  <span  >temporal</span>


<p  >

  <span  >placement</span>


The implementation can treat the points T and T+1 as key-frames in an animation to smooth the transition, as this is apparently preferred by US viewers, in the UK however line-at-a-time jumps are more common.

From: Silvia Pfeiffer [mailto:silviapfeiffer1@gmail.com]
Sent: 06 August 2012 17:26
To: Sean Hayes
Cc: Goldstein, Glenn; public-tt@w3.org
Subject: Re: Re: questions on simple profile - nested spans

I have a question, too.

The document presents this as an example for rollup captions:

<p region='rollup' begin='00:00:13.000' dur='00:00:11.000'>

  <span begin='00:00:01.000'>rollup</span>

  <span begin='00:00:02.000'>style</span>

  <span begin='00:00:03.000'>caption</span>

  <span begin='00:00:04.000'>support</span>


<p region='rollup' begin='00:00:17.000' dur='00:00:11.000'>

  <span begin='00:00:01.000'>with</span>

  <span begin='00:00:02.000'>word</span>

  <span begin='00:00:03.000'>at</span>

  <span begin='00:00:04.000'>a</span>

  <span begin='00:00:05.000'>time</span>

  <span begin='00:00:06.000'>temporal</span>


<p region='rollup' begin='00:00:23.000' dur='00:00:11.000'>

  <span begin='00:00:01.000'>placement</span>

  <span begin='00:00:02.000'>this</span>

  <span begin='00:00:03.000'>could</span>

  <span begin='00:00:04.000'>go</span>


<p region='rollup' begin='00:00:27.000' dur='00:00:11.000'>

  <span begin='00:00:01.000'>on</span>

  <span begin='00:00:02.000'>all</span>

  <span begin='00:00:03.000'>day</span>


Would you mind explaining how this works?
I am particularly confused about where the rollup happens. I assume that the words within the <p> element are all on the same line, but appear one at a time.

That leads me to the conclusion that each <p> will be rendered on the same default position. Does that mean that the <p> elements push each other out of the way?
How does that work technically: when you add a <p> on top of an existing <p> in the same location, is it added below and the previous <p> pushed upwards?

I wasn't able to find that specified in the document. Sorry for my ignorance.

Received on Tuesday, 7 August 2012 18:03:55 UTC

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