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proposal to replace dynamicFlow

From: Geoff Freed <geoff_freed@wgbh.org>
Date: Wed, 28 Jan 2009 08:51:02 -0500
To: Public TTWG List <public-tt@w3.org>
Message-id: <C5A5CCF6.52BB%geoff_freed@wgbh.org>

Partly in support of Andrew's message  at http://lists.w3.org/Archives/Public/public-tt/2008Dec/0137.html, partly as a counter-proposal to Sean's proposal at http://lists.w3.org/Archives/Public/public-tt/2008Dec/0142.html, and partly as a way to rethink the way DFXP supports pre-produced roll-up captions/subtitles, I submit the following proposal for the replacement of dynamicFlow.  This is a base proposal; I expect it to receive a severe beating and, I hope, many improvements while remaining as simple as possible.

PROPOSAL:  Delete <tts:dynamicFlow> from DFXP.  Replace it with a new element, <tts:rollUp>, which governs only the behavior of roll-up text.  Other dynamic displays, such as crawls, should be defined separately.

Here are the basic properties of <tts:rollUp>:

1.  Has at least two attributes:
    -- enable, with the values "on" and "off". Initial value is "off".
    -- depth, which specifies the maximum number of rows that are displayed at one time.  Values are any non-negative integer.  Initial value is "3".

Andrew's message includes a feature which could be very useful if applied to <region>:  "Leverage the proposed upperThird/middleThird/lowerThird region tag to allow for the rollup caption area to be positioned appropriately on the screen. Software that converts 608/708 captions to timed text can inspect the line positioning and infer the appropriate screen region."  I'm not sure how to handle this, however.

2.  Can be applied to <region>, <body>, <div> or <p>.

3.  Has fixed timing and scrolling behavior which emulates that specified in EIA-608:  "... the text in the top row of the window is erased from memory and from the display or scrolled off the top of the window. The remaining rows of text are each rolled up into the next highest row in the window, leaving the base row blank and ready to accept new text. This roll-up must appear smooth to the user, and must take no more than 0.433 second to complete."   (excerpted from "Closed Caption Decoder Requirements for Analog Television Receivers"; full doc at http://edocket.access.gpo.gov/cfr_2005/octqtr/47cfr15.119.htm)

4.  A row of text does not paint horizontally or "unroll" into the region when it appears; it simply scrolls up in its entirety.

5.  The currently displayed bottom row of text need not be full in order to force the display to roll up.  That is, if the bottom row ends with a linefeed or a <br />, the next row will roll up regardless of the length of the current row.

Example usage:

<?xml version="1.0" encoding="utf-8"?>
<tt xml:lang="en"
      <ttm:title>Example: rollUp</ttm:title>
        <region xml:id="r1">
            <style tts:backgroundColor="black"/>
            <style tts:color="white"/>
            <style tts:fontSize="14px"/>
            <style tts:origin="0px 240px"/>
            <style tts:extent="320px 150px"/>
            <style tts:displayAlign="after"/>
            <style tts:rollUp="enable(on) depth(2)"/>
          <p region="r1">
            <span begin="00:00:01.00">How doth the little crocodile</span>
            <span begin="00:00:03.00">Improve its shining tail;</span>
              <span begin="00:00:05.00">And pour the waters of the Nile</span>
              <span begin="00:00:07.00">On every golden scale!</span>
              <span begin="00:00:09.00">How cheerfully he seems to grin,</span>
              <span begin="00:00:11.00">How neatly spreads his claws,</span>
              <span begin="00:00:13.00">And welcomes little fishes in</span>
              <span begin="00:00:15.00">With gently smiling jaws!</span>
              <span begin="00:00:17.00"><br /></span>
              <span begin="00:00:19.00"><br /></span>

Received on Wednesday, 28 January 2009 13:51:49 UTC

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