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TTML / tts:showBackground='always'

From: <sylvain.kervadec@orange.com>
Date: Wed, 7 Dec 2016 09:41:53 +0000
To: "public-tt@w3.org" <public-tt@w3.org>
Message-ID: <25100_1481103714_5847D962_25100_471_1_F8ECA7CAF25D0B4AA957200EF98235A22675C1BC@OPEXCLILM41.corporate.adroot.infra.ftgroup>
Dear tt experts,

            I am looking for some clarifications on the expected behavior of the tts:showBackground parameter defined on a temporally inactive region.
To be more specific, I would like to know if the background of a temporally inactive region with a tts:showBackground equal to 'always' shall be displayed or not.
The topic has already been discussed (https://www.w3.org/AudioVideo/TT/tracker/issues/314, and 313, 330), but I still don't know what is the correct answer.

I am using TTML2 as a reference, as it introduces some missing definitions on active regions:
The tts:showBackground definition says that "the background color of a region is always rendered when performing presentation processing on a visual medium", when its value is equal to 'always'.
However, the text also says "For the purpose of determining the semantics of presentation processing, a region that is temporally inactive must not produce any visible marks when presented on a visual medium."
Reading IMSC1, "A presented region is a temporally active region that satisfies the following conditions:.." seems to indicate that an inactive region shall not be presented.

My understanding is thus that an inactive region shall not be displayed, whatever the value of tts:showBackground, but I would appreciate your guidance on the topic.

Here is an example:

<?xml version="1.0" encoding="UTF-8"?>
<tt xml:lang="fre" xmlns="http://www.w3.org/2006/10/ttaf1" xmlns:ttp="http://www.w3.org/2006/10/ttaf1#parameter" xmlns:tts="http://www.w3.org/2006/10/ttaf1#styling" ttp:cellResolution="50 30">
   <head>
      <styling>
         <style xml:id="ts0" tts:fontFamily="monospaceSansSerif" tts:lineHeight="1c" tts:textDecoration="none" tts:fontWeight="normal" tts:fontStyle="normal" tts:fontSize="1c 1c" tts:color="#FFFFFFFF" tts:backgroundColor="#00000064" tts:textOutline="#000000FF 0.1c 0c"/>
         <style xml:id="ts1" tts:lineHeight="2c" tts:textDecoration="none" tts:fontWeight="normal" tts:fontStyle="normal" tts:fontSize="1c 2c" tts:color="#FFFFFFFF" tts:backgroundColor="#00000064" tts:textOutline="#000000FF 0.1c 0c"/>
         <style xml:id="ps0" tts:textAlign="center"/>
      </styling>
      <layout>
         <region xml:id="r0" tts:origin="10% 73%" tts:extent="80% 17%" tts:displayAlign="before"/>
         <region xml:id="r1" tts:origin="10% 66%" tts:extent="80% 24%" tts:displayAlign="before"/>
      </layout>
   </head>
   <body>
      <div style="ts0">
         <p region="r0" begin="00:00:00.280" end="00:00:01.640" style="ps0">
            <span style="ts1" xml:space="preserve">extirpé ?</span>
         </p>
         <p region="r0" begin="00:00:02.720" end="00:00:04.840" style="ps0">
            <span style="ts1" xml:space="preserve">Je dois dire que...</span>
         </p>
         <p region="r0" begin="00:00:07.880" end="00:00:09.960" style="ps0">
            <span style="ts1" xml:space="preserve">mes yeux sont verts, en fait.</span>
         </p>
         <p region="r1" begin="00:00:11.360" end="00:00:11.360" style="ps0">
            <span style="ts1" xml:space="preserve">Je ne qualifierais pas</span>
         </p>
         <p region="r1" begin="00:00:11.360" end="00:00:13.280" style="ps0">
            <span style="ts1" xml:space="preserve">Je ne qualifierais pas</span>
            <br/>
            <span style="ts1" xml:space="preserve">notre réticence</span>
         </p>
      </div>
   </body>
</tt>

The tts:showBackground defaults to 'always'.
Two overlapping regions are defined (for single-line and two-lines subtitles), only one being active at any time.
If we have to display the background for inactive regions, it does not look good, as we have two semi-transparent regions on top of each other.
Adding tts:showBackground='whenActive' would solve our problem, but our contents have been generated without any tts:showBackground value so far.


Thanks in advance for your help.
Best regards,
Sylvain




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Received on Wednesday, 7 December 2016 09:43:21 UTC

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