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> 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
<https://www.w3.org/AudioVideo/TT/tracker/issues/312> Issue-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