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