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Re: ISSUE-339 (allow #overflow): Allow the use of #overflow [TTML IMSC 1.0]

From: Pierre-Anthony Lemieux <pal@sandflow.com>
Date: Wed, 24 Sep 2014 15:39:45 -0700
Message-ID: <CAF_7JxDubMDaP3kLv-iOj4UBn34J5qnKOVw33aPwWRZ9jnQr0g@mail.gmail.com>
To: Timed Text Working Group <public-tt@w3.org>
Addressed at https://dvcs.w3.org/hg/ttml/rev/82c18c2fe212

Best,

-- Pierre

On Wed, Aug 27, 2014 at 1:28 PM, Timed Text Working Group Issue
Tracker <sysbot+tracker@w3.org> wrote:
> ISSUE-339 (allow #overflow): Allow the use of #overflow [TTML IMSC 1.0]
>
> http://www.w3.org/AudioVideo/TT/tracker/issues/339
>
> Raised by: Frans de Jong
> On product: TTML IMSC 1.0
>
> ---------------------------------------------------------------
> Request
> ---------------------------------------------------------------
> Section 5.8 (Common Constraints->Features)
>
> It shall be possible to use the #overflow feature.
>
> Needed change
>
> Now:
> #overflow -> SHALL NOT be used
>
> Proposed
> #overflow->MAY be used
>
>
> If this editorial change is not feasible the second (but worse option) would be to add a requirement that a processor should not stop processing the document even if it contains the unsupported tts:overflow attribute.
>
>
> ---------------------------------------------------------------------------------------------
> Background
> ---------------------------------------------------------------------------------------------
> In IMSC the use of overflow is not allowed. It is not defined if a processor is allowed to reject a document that uses tts:overflow.
>
> The assumed behaviour in IMSC is tts:overflow="hidden". As this is the TTML initial value and "visible" is not allowed, the feature is prohibited entirely.
>
> In EBU-TT-D it is specified that
>
>                                  If the value of this attribute is “visible", then content
>                                     should not be clipped. If the value is hidden, then content that
>                                     goes outside of the affected region should be clipped and is not
>                                     visible
>
> Further it is added in an informative note:
>
>                    Note:        Setting the feature to “visible” does not
>                                     guarantee that content that overflows the region will be
>                                     presented, e.g. if the content would need to overflow the root
>                                     container region.
>
> Therefore if the default behaviour is applied (content that overflows is hidden) the processor behaviour will still be EBU-TT-D compliant and acceptable. But a processor shall not reject the document and shall process it.
>
> It would be better to enable the feature to make IMSC more consistent. As the implied presentation behaviour is not a strict requirement for a presentation processor it should not cause any problem for any existing processor that has not implemented this feature yet.
>
>
>
>
Received on Wednesday, 24 September 2014 22:40:36 UTC

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