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RE: question re: streaming caption data format

From: Sean Hayes <Sean.Hayes@microsoft.com>
Date: Tue, 21 Oct 2008 10:24:03 +0100
To: "public-tt@w3.org" <public-tt@w3.org>
Message-ID: <90EEC9D914694641A8358AA190DACB3D2802C88B82@EA-EXMSG-C334.europe.corp.microsoft.com>

It seems to me that from an authoring point of view, especially live, being able to pre-design combinations; and then have these triggered by role/agent changes would be a convenient and flexible solution. I could imagine in a future specification, (and we have discussed this before in the context of AFXP), being able to have <style> elements which support some kind of media query, or a CSS like applicative style mechanism, to have style be conditional on attribute values.

NB region cannot hold a metadata attributes; and there is no role element (probably a mistake IMO).

However that is for the future. The actual scenario being discussed here is not so much changing the layout, but rather where the viewer breaks into a stream partway through and hasn't acquired the layout block. This doesn't really happen today in on-demand scenarios on the web, whether true streaming, or just download and play, as the bi-directional protocols allow you to get the caption data out of band or on demand; but is more likely to start happening in true multi-cast and IPTV type scenarios. For this the ability to periodically resend the <layout> block would be convenient. I personally don't think this is something we have to solve in DFXP 1.0 though, and it seems to me largely a lower level protocol and tooling issue.

In terms of compatibility with US captioning, 708 allows for only 8 region definitions at any one time, but does have the capability to destroy and create them on the fly thus has potentially a very large set of combinations over time. Thus DFXP, in order to capture/recreate a long complex 708 sequence, may end up needing a lot of region definitions. But again I think this is more theoretical than reflecting reality, in practice I expect a fairly small set of design combinations get used.

Sean Hayes
Media Accessibility Strategist
Accessibility Business Unit
Microsoft

Office:  +44 118 909 5867,
Mobile: +44 7875 091385


-----Original Message-----
From: public-tt-request@w3.org [mailto:public-tt-request@w3.org] On Behalf Of John Birch
Sent: 21 October 2008 09:29
To: Andrew Kirkpatrick; public-tt@w3.org
Subject: RE: question re: streaming caption data format


Andrew,

If by captioning you are referring to US 608 and 708 captions for the
hard of hearing then I would agree.
In the UK, Europe and other global locations :-) subtitles (translation)
often uses colour changes to indicate a change of speaker.
Italics are frequently used to distinguish off screen narration from on
screen speakers, or music lyrics from spoken words.

While these effects are more commonly used for pre-coded subtitles, they
are used for true live subtitling too.
BTW by live subtitling, I mean subtitles generated without a priori
knowledge of the dialogue in real time.
In live subtitling, there can be no pre-transmission of styles, sinc3
there is no knowledge of what styles may be used... Although it is
feasible that all the potential combinations could be collected in the
header on the chance that they might be used during the performance...
However, this strikes me as somewhat in-elegant :-)

Of course, pre-coded subtitles might be used for the playout of a video
stream and be transmitted in a streaming manner, where for whatever
reason the downloading of the entire subtitle stream at the commencement
of clip playback is undesirable (e.g. when wishing to play from the
middle of a larger asset).

Regards,

John

John Birch | Screen Subtitling Systems Ltd | Strategic Partnerships Manager
Main Line : +44 (0)1473 831700 | Ext : 270 | Office :
Mobile: +44 (0)7919 558380 | Fax: +44 (0)1473 830078
john.birch@screen.subtitling.com | www.screen.subtitling.com
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-----Original Message-----
From: public-tt-request@w3.org [mailto:public-tt-request@w3.org] On
Behalf Of Andrew Kirkpatrick
Sent: 21 October 2008 03:06
To: public-tt@w3.org
Subject: question re: streaming caption data format


DB: Header information is fixed like it is in DFXP. Supports out of band
styling, but no in stream styling. Canuse smil param elements as the out
of band mechanism.

Related to the discussion last week - what is the use case that we are
trying to support where the caption or other text stream needs to change
format?  I may be thinking too narrowly around captioning, but the case
where captions are streaming it is all that the captioner can do to get
the text of the captions into the stream, forget about modifying the
style...  Are there current cases where this is needed?

Thanks,
AWK



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Received on Tuesday, 21 October 2008 09:25:18 GMT

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