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timed roll-up captions: sample video and code

From: Geoff Freed <geoff_freed@wgbh.org>
Date: Thu, 05 Feb 2009 12:06:19 -0500
To: Timed Text Working Group WG <public-tt@w3.org>
Message-id: <C5B086BB.5637%geoff_freed@wgbh.org>

i've uploaded a 20-second demo clip of pre-timed roll-up captions at http://ncamftp.wgbh.org/geoff/tcru2+3_ttwg.mov .  i've added annotations which point out basic features.  the quality is low but you'll get the idea.  note the following:

--  each row of text scrolls in and out smoothly
--  the appearance of text from left to right is smooth and continuous
--  the maximum number of rows (three or two), as well as the position of the regions, changes on the fly

below is what brad and i think the caption file for this clip would look like using current DFXP markup to emulate EIA-608 behavior.  note that rather than create two regions (one for captions in the upper third and one for lower third), i've animated the origin and extent of a single region.

<?xml version="1.0" encoding="utf-8"?>
<tt xml:lang="en"
    ttp:cellResolution="32 15">
      <ttm:title>Example: roll-up captions with animated regions</ttm:title>
        <region xml:id="captions">
            <style tts:backgroundColor="black"/>
            <style tts:color="white"/>
            <style tts:fontSize="14px"/>
            <style tts:origin="1c 1px"/>
            <style tts:extent="32c 2px"/>
            <style tts:displayAlign="after"/>
            <style tts:dynamicFlow="in(line,smooth) out(line,smooth)"/>
            <set begin="00:00:00.00" end="00:00:14.21" tts:origin="1c 1c" tts:extent="32c 2c"/>
            <set begin="00:00:14.21" end="00:00:19.73" tts:origin="1c 13c" tts:extent="32c 3c"/>
            <set begin="00:00:19.73" end="23:23:59.00" tts:visibility="hidden"/>

          <p region="captions">
            <span begin="00:00:09.63">&gt; &gt; JAMIE: Well, this week I'm</span>
            <span begin="00:00:01.58">starting at the Getty Museum</span>
            <span begin="00:00:02.79">here in Los Angeles, at Robert</span>
            <span begin="00:00:04.42">Irwin's famous Central Garden.</span>
            <span begin="00:00:06.63">And in particular focusing on</span>
            <span begin="00:00:08.15">these incredible espaliered</span>
            <span begin="00:00:10.00">bougainvilleas up these manmade</span>
            <span begin="00:00:12.15">steel trees.</span>
            <span begin="00:00:14.21">They're made out of steel</span>
            <span begin="00:00:15.15">reinforcing, and they're just</span>
            <span begin="00:00:16.42">incredible.</span>
            <span begin="00:00:17.05">Come on, I'll show you.</span>
            <span begin="00:00:19.73"><br /></span>


as currently structured, there's no way to know by looking at the content area that these captions are supposed to be roll-up captions--  for that information, you need to look at the layout.  ideally an author ought to be able to explicitly state in the content area that a block of text is roll-up captions.  in addition (and to follow up on something we discussed on last week's call), it would be useful to have a tag that contains inherent roll-up characteristics which emulate 608 behavior, streamlining the authoring of roll-up captions.  let's say the tag is called <608rollUp> and embodies the following fixed behavior:

--  smooth scrolling of rows as they scroll into and out of the region <tts:dynamicFlow="in(line,smooth) out(line,smooth)>"
--  a scrolling speed that corresponds to that specified by EIA-608 (.433 seconds)
--  smooth appearance of characters as they paint in from left to right
-- a safe area corresponding to a 5% margin (padding, i suppose...) on all four sides
-- a 32c x 15c layout (which is DFXP's current default ttp:cellResolution)
-- a region that is black and persistent when it is visible, which differs from 608 behavior where the region is transparent and the characters have a background color
-- a font size which is not specified by the author but is instead determined by the user agent, relative to the size of the root container, and which fits into th 32c x 15c raster

an idea worthy of further discussion?

Received on Thursday, 5 February 2009 17:07:05 UTC

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