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ISSUE-332 (-): #cellResolution support [TTML IMSC 1.0]

From: Timed Text Working Group Issue Tracker <sysbot+tracker@w3.org>
Date: Thu, 07 Aug 2014 12:22:00 +0000
Message-Id: <E1XFMhk-0005Vt-S6@shauna.w3.org>
To: public-tt@w3.org
ISSUE-332 (-): #cellResolution support [TTML IMSC 1.0]

http://www.w3.org/AudioVideo/TT/tracker/issues/332

Raised by: Frans de Jong
On product: TTML IMSC 1.0

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Request
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Chapter 4.8 (Common Constraints -> Features)

The part:

"#cellResolution  SHALL NOT be used."

should be deleted.

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Reasoning
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IMSC currently does not allow the use of the feature #cellResolution
https://dvcs.w3.org/hg/ttml/raw-file/tip/ttml-ww-profiles/ttml-ww-profiles.html#features

It is not sufficient that an IMSC processor processes the EBU-TT-D document but ignores cellResolution values. Indirectly the cellResolution defines the fontSize. IMSC calculates the fontSize in percentages with an implicit cellResolution (with the TTML initial value, "32 15"). EBU-TT-D documents  (example here: http://tech.ebu.ch/docs/ebu-tt/ebu-tt-d-imsc-compliance-example.xml ) will renderin a different font-size and therefore intended line breaks cannot be guaranteed. In this use case this is not acceptable for the broadcaster.

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General use case
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A german broadcaster uses an EBU-TT-D document (https://tech.ebu.ch/docs/ebu-tt/ebu-tt-d-imsc-compliance-example.xml) for HbbTV subtitles and for their catch up tv - portal for PC. Both the HbbTV application (or in the future the HbbTV 2.0 compliant device) and the player of the EBU-TT-D portal support EBU-TT-D. Now the broadcaster licences the same AV content together with the subtitles to a commercial on-demand Internet streaming media provider. The provider distributes its content to a client which is conformant to IMSC 1.0 (IMSC 1.0 Text - http://www.w3.org/ns/ttml/profile/imsc1/text). Conformance to EBU-TT-D of this player is not documented.

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Requirement
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The broadcaster demands from the provider that the subtitles will be displayed as specified in the EBU-TT-D file. The provider will distribute the EBU-TT-D file as it is provided and will not convert the EBU-TT-D file.
Received on Thursday, 7 August 2014 12:22:02 UTC

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