RE: ISSUE-309 (Image profile fails WCAG 1.2): Image profile needs to permit text equivalent [TTML IMSC 1.0]

I find it difficult to reconcile a design decision with a requirement... unless the original CFF(?) use case explicitly demanded a single document...(which is not clear from below) ;-)

Regardless... I understand the desire to simplify the implicit requirements on a notional processor to only loading, decoding and rendering a single document and therefore I do generally support the forcedDisplayMode concept.
For me this is the inclusion of two logical streams of (connected) content within a single document. Further, I do see this as setting a precedent. :)

With regards to adding text to the image profile, the proposal was only ever to consider the text as 'alternative content'. However,  I would suggest that a 'useful' implementation might make the text available to another process or output device whilst also still decoding the images. (e.g. support text output to a braille display simultaneously to image rendering). I agree that the text should not be considered 'normal TTML text' as (under that specification) it would need to be displayed. Instead I suggest that the (equivalent) alternative text should be included as an attribute of the image... and thus could not have an independent existence from an image?

Ideally I would like this to be a change to the current IMSC specification.

Best regards,
John

John Birch | Strategic Partnerships Manager | Screen
Main Line : +44 1473 831700 | Ext : 2208 | Direct Dial : +44 1473 834532
Mobile : +44 7919 558380 | Fax : +44 1473 830078
John.Birch@screensystems.tv<mailto:John.Birch@screensystems.tv> | www.screensystems.tv<http://www.screensystems.tv> | https://twitter.com/screensystems

Visit us at
Broadcast Asia, Marina Bay Sands, Singapore 17-20 June, Stand 5E4-01

P Before printing, think about the environment

From: Michael Dolan [mailto:mdolan@newtbt.com]
Sent: 12 June 2014 14:21
To: 'Timed Text Working Group'
Subject: RE: ISSUE-309 (Image profile fails WCAG 1.2): Image profile needs to permit text equivalent [TTML IMSC 1.0]

In this case, it is less about whether we agree.  I am clarifying what the requirements are in the liaison. The design for a single document with forcedDisplayMode was developed by a collection of movie subtitle authoring companies, and a collection of device manufacturers.  Us debating alternative designs doesn't change the requirements. If W3C designs something else that requires simultaneous multiple document decoding and merged presentations, that would fail to meet the requirements.

Regarding adding text to the image profile:

"...including text in image profile documents would be an acceptable solution to you."

Yes, as long as it is not required, and it is clearly signaled as "alternative" text in some manner.  It would be incorrect to include normal TTML text since that would have to be displayed and thus result in totally incorrect output.

Regards,

                Mike

From: Nigel Megitt [mailto:nigel.megitt@bbc.co.uk]
Sent: Thursday, June 12, 2014 5:51 AM
To: Michael Dolan; 'Timed Text Working Group'
Subject: Re: ISSUE-309 (Image profile fails WCAG 1.2): Image profile needs to permit text equivalent [TTML IMSC 1.0]

I understand the argument but I don't agree. This may come down to a 'system model' difference.

They are both schemes in which multiple conceptually different content streams need to be made available, and the presentation of one or or more from the group is conditional on settings in the decoder, perhaps defined by the user.

One could equally well generate a solution in which for 'forced display' content the content provider must provide two or more documents and ensure that the combined content of the group never exceeds the constraints of a single document, in complexity, overlapping regions, xml identifiers etc. Then the decoder must select the content from the appropriate documents and combine them client-side for display, which could be a defined 'pre-processing' task.

If necessary we could even signal within documents 'this forms part of a group that may be combined for collective presentation' with a new 'group identifier'. Documents with different group identifiers would offer no guarantee that they may successfully be combined in this way.

A solution like this would be extensible for live streams in which a group of temporally consecutive documents could be assigned the same group identifier and successfully combined for presentation - in that case they would probably be exclusive to each other temporally rather than spatially.


By the way, Mike, I note that you've previously indicated that including text in image profile documents would be an acceptable solution to you.


Kind regards,

Nigel


On 12/06/2014 12:34, "Michael Dolan" <mdolan@newtbt.com<mailto:mdolan@newtbt.com>> wrote:

They are not the same.

forcedDisplayMode text is embedded in a single document since otherwise a decoder would have *simultaneously* decode two documents (one with forced content and one with non-forced content) and merge the output over the visual object.

The desire to force the image profile to contain alternate text is solved with a text profile document.  Only one or the other document is decoded and presented since they each produce substantively the same visual results. And, even if it is desirable to decode both simultaneously, they would not have to be merged onto the visual object.

Regards,

                Mike

From: Nigel Megitt [mailto:nigel.megitt@bbc.co.uk]
Sent: Thursday, June 12, 2014 4:10 AM
To: 'Timed Text Working Group'
Subject: Re: ISSUE-309 (Image profile fails WCAG 1.2): Image profile needs to permit text equivalent [TTML IMSC 1.0]

I've updated this issue with the following note:

The proposed resolution to this is not consistent with the approach taken for forcedDisplay (see also Issue-312<https://www.w3.org/AudioVideo/TT/tracker/issues/312>). In the latter case it is stated that the two types of content must be provided in the same document. In this case it is stated that the content provider may optionally provide multiple documents.

A simple resolution to this would be to permit text to be included in the image profile.


Nigel


This message may contain confidential and/or privileged information. If you are not the intended recipient you must not use, copy, disclose or take any action based on this message or any information herein. If you have received this message in error, please advise the sender immediately by reply e-mail and delete this message. Thank you for your cooperation. Screen Subtitling Systems Ltd. Registered in England No. 2596832. Registered Office: The Old Rectory, Claydon Church Lane, Claydon, Ipswich, Suffolk, IP6 0EQ