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RE: ISSUE-1 (dynamicFlow): dynamicFlow in DFXP cannot emulate an important feature of EIA-608 captions

From: Glenn A. Adams <gadams@xfsi.com>
Date: Fri, 19 Sep 2008 10:16:06 -0400
Message-ID: <C0A7A8BF0F28BA4B9C6C8816309E1D0726C39F@ES1.xfsi.com>
To: "John Birch" <john.birch@screen.subtitling.com>, "Timed Text Working Group WG" <public-tt@w3.org>


as was just pointed out in telecon, DFXP permits moving regions and
making them visible/invisible by dynamic means; namely, by using
<tt:set/> animation element; furthermore, one can use tts:showBackground
to automatically control visibility according to whether region has
content selected into it or not;

one (current) limitation, however, is that all of the animation on a
region using <tt:set/> must appear as a descendant of a <tt:region/>
element, which appears only in the document's header (in <tt:head/>). if
this limitation is problematic, then perhaps it would be possible to
permit specifying <tt:set/> under a content element with a region
attribute, e.g.,

<tt:p region="r0" begin="10s" dur="5s">
<tt:set region="r0" tts:origin="100px 100px" tts:visibility="visible"/>
...
</tt:p>

here the content of this div would be flowed into region r0, and,
furthermore, the animation element would apply to that region (and be
temporally co-terminus) as well;

> -----Original Message-----
> From: public-tt-request@w3.org [mailto:public-tt-request@w3.org] On
Behalf Of John Birch
> Sent: Friday, September 19, 2008 10:06 AM
> To: Timed Text Working Group WG
> Subject: RE: ISSUE-1 (dynamicFlow): dynamicFlow in DFXP cannot emulate
an important
> feature of EIA-608 captions
> 
> 
> Hi Geoff,
> 
> You raise an interesting point.
> 
> I agree, in all captioning systems it is possible to locate captions
as
> appropriate to avoid other on-screen activity.
> In a live presentation, in a TV captioning scenario, the location of
the
> captions may often be controlled as you describe by the captioner /
> subtitler.
> In some cases captions are automatically relocated under control of
> automation or other equipment (for example - logo insertion
equipment).
> 
> 
> Note: In the US systems [608 and 708], captions may be relocated **by
> the viewer**
> Incidentally - this is unique to 608/708 captioning methods, all other
> TV captioning standards do not allow the viewer to control caption
> presentation sytle (including position), only caption visibility.
> 
> Yet, for the DFXP scenario I am undecided if the problem you describe
> does actually exist.
> 
> As mentioned above, for a pre-recorded media asset the captions can be
> correctly located because the captioner has a priori knowledge.
> 
> However, for a 'live' asset, it is not possible to use the standard
DFXP
> mechanism (a single DFXP file) for the captioning - since parsing of
> that file requires a complete file to be present (in theory if not in
> practice :-). Hence the streamed DFXP that was introduced into DFXP.
> 
> Would it not be possible to create locations for dynamic flowed
content
> that exist only within each of the units of DFXP that are streamed?
> I confess to not having that aspect of the CR in my head... So
apologies
> if this is invalid. But my understanding was that the streamed version
> of DFXP was intended to cater for this type of issue... That is a lack
> of a priori knowledge about what needs to be transmitted...
> 
> BTW - my main concerns about dynamic flow are that it won't actually
> work (as I think it needs to) under the CR proposal :-)
> 
> Note: - I do not equate 'live captioning' with dynamic flow... I see
> dynamic flow as equally valid for a downloaded media asset with
captions
> (in which case dynamic flow is a means to avoid timing and flowing all
> the captions explicitly).
> 
> Yours sincerely,
> 
> John Birch
> 
> 
> John Birch | Screen Subtitling Systems Ltd | Strategic Partnerships
Manager
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> 
> -----Original Message-----
> From: public-tt-request@w3.org [mailto:public-tt-request@w3.org] On
> Behalf Of Timed Text Working Group Issue Tracker
> Sent: 19 September 2008 14:43
> To: public-tt@w3.org
> Subject: ISSUE-1 (dynamicFlow): dynamicFlow in DFXP cannot emulate an
> important feature of EIA-608 captions
> 
> 
> ISSUE-1 (dynamicFlow): dynamicFlow in DFXP cannot emulate an important
> feature of EIA-608 captions
> 
> http://www.w3.org/AudioVideo/TT/tracker/issues/1
> 
> Raised by: Geoff Freed
> On product:
> 
> One of my concerns about the current dynamicFlow in DFXP is that it
> cannot emulate an important feature of EIA-608 captions, which is the
> ability to create and change regions on the fly.  Currently,
dynamicFlow
> can feed text into pre-created regions in pre-specified locations.  In
a
> real-time-captioning situaton, region locations may not be known ahead
> of time, and during a broadcast blocks of caption text sometimes have
to
> be moved from, say, the lower-third of the picture to the upper-third
to
> avoid covering important graphics, or sometimes they are just moved up
> (or down) one or two rows.  As far as I know, DFXP does not allow to
> on-the-fly creation of new regions, does it?  If not, then the current
> dynamicFlow isn't really suited for live captioning or subtitling, and
> this is something that I'd like to improve, it if is possible within
the
> bounds of the charter.
> 
> 
> 
> 
> 
> 
> 
> 
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Received on Friday, 19 September 2008 14:16:50 GMT

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