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Re: ACTION-329: Revisit issue-339 to investigate potential resolution options

From: Glenn Adams <glenn@skynav.com>
Date: Tue, 23 Sep 2014 07:37:49 -0600
Message-ID: <CACQ=j+fHN0VXpezQnxG=MBgXa9BArc6zpYRqJwGBoJreSztMxQ@mail.gmail.com>
To: "De Jong, Frans" <dejong@ebu.ch>
Cc: Timed Text Working Group <public-tt@w3.org>

On Tue, Sep 23, 2014 at 4:32 AM, De Jong, Frans <dejong@ebu.ch> wrote:

> Dear all,
> I have followed up ACTION-329. Please find here the result as it was
> agreed during the EBU Subtitling Group's meeting last Friday.
> Best regards,
> Frans
> -- Response on Issue-339
> 1. Intention of EBU-TT-D usage of tts:overflow.
> Presentation of text is the primary goal of the EBU-TT-D use cases; whilst
> unexpected overflow of text is undesirable, in a chain that can not be
> fully constrained in regards to fonts and text layout it is considered
> unavoidable. It is considered a worse option to clip overflowed text and
> potentially change the editorial meaning as read by the user than to permit
> presentation engines to try to display the text.
> 2. Interpretation of TTML1 tts:overflow wording.
> EBU interpreted the text of TTML 1 SE tts:overflow as follows:
> •       The region size is unaffected by overflow.
> •       Wrapping of text, when wrapOption=“wrap” is bounded by the size of
> the region.
> •       Line areas flowed into a region may be affected by overflow, and
> they may be rendered outside the region if tts:overflow=“visible”.
> •       We expect presentation processors to clip all content outside the
> region area if tts:overflow=“hidden”.
> •       The default behaviour if tts:overflow is unspecified is to process
> the document according to the initial value “hidden”, which could in some
> cases, that we are unable to control, result in some text being hidden.
> 3. Interpretation of IMSC 1 current wording.
> EBU interprets the prohibition of tts:overflow from IMSC 1 documents as a
> directive that the initial value of tts:overflow, “hidden”, applies and
> that processors are therefore expected to clip text that happens to fall
> outside the region.
> 4. Mitigation approaches.
> EBU would support a recommendation that documents should be authored
> assuming the ‘worst case scenario’, i.e. with strict clipping of content
> that falls out of region areas, regardless of the value of tts:overflow in
> the document.
> EBU proposes a change to IMSC 1 to make clear that presentation processors
> shall be permitted to display text that overflows the region, indicated
> within documents by use of tts:overflow=“visible”:
>         “NOTE: Presentation processors are permitted to display text that
> overflows the region if tts:overflow=“visible”. “
> In order to permit those processors to show overflowed text, the value
> “visible” must be permitted within IMSC 1 documents. This change requires
> that the #overflow feature be changed to MAY be permitted in IMSC 1, as
> requested in Issue-339.
> As a minimum, even in the absence of any functionality to display or
> indeed clip overflowed text, presentation processors should be permitted to
> process documents that have a tts:overflow attribute set either to “hidden”
> or “visible”.
> EBU would support an erratum to TTML1SE that clarifies that the intended
> meaning of the tts:overflow wording is as stated in 2. above. Specifically
> it must be clear that, for the purposes of drawing region backgrounds and
> calculating wrapping, the region size is unaffected by the value of
> tts:overflow.
> 4. Impact on TTML2.
> EBU does not consider tts:overflow a complete solution to the rendering
> and presentation problems that may occur, and
> may propose, or would support in principle, overflow avoidance strategies,
> for example copy-fit (aka shrink to fit) algorithms, or
> attribute-controlled direction for processors to adjust region origin and
> size to maintain the presentation of text within a region.
> -----Original Message-----
> From: Timed Text Working Group Issue Tracker [mailto:sysbot+tracker@w3.org
> ]
> Sent: mercredi 17 septembre 2014 14:43
> To: public-tt@w3.org
> Subject: ACTION-329: Revisit issue-339 to investigate potential resolution
> options
> ACTION-329: Revisit issue-339 to investigate potential resolution options
> http://www.w3.org/AudioVideo/TT/tracker/actions/329
> Assigned to: Frans de Jong
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Received on Tuesday, 23 September 2014 13:38:36 UTC

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