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

From: John Birch <john.birch@screen.subtitling.com>
Date: Fri, 19 Sep 2008 15:06:20 +0100
Message-ID: <4476B296B92A4741A49B0BD0175907009EB267@sss-uk-ex-02.screen.subtitling.local>
To: "Timed Text Working Group WG" <public-tt@w3.org>

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


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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 14:07:02 GMT

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