- From: <Johnb@screen.subtitling.com>
- Date: Thu, 17 Mar 2005 17:32:33 -0000
- To: public-tt@w3.org
- Message-ID: <11E58A66B922D511AFB600A0244A722EE57D88@NTMAIL>
Glenn,
Comments inline
-----Original Message-----
From: Glenn A. Adams [mailto:gadams@xfsi.com]
Sent: 17 March 2005 16:11
To: Johnb@screen.subtitling.com; public-tt@w3.org
Subject: RE: Timed Text Authoring Format - Distribution Format Exchange Pr
ofile (DFXP)
_____
From: Johnb@screen.subtitling.com [mailto:Johnb@screen.subtitling.com]
Sent: Thursday, March 17, 2005 9:53 AM
To: public-tt@w3.org
Subject: RE: Timed Text Authoring Format - Distribution Format Exchange Pr
ofile (DFXP)
Glenn,
As defined, the use of referential styles already requires head fragments to
be repeated throughout a stream transmission to permit mid-stream
acquistition. A stream unit is not directly parsable if it uses referential
styling, because it will require lookup in this 'head' fragment.
So it would seem that the sole reason for not including class based (or rule
based) styling is the need for "re-evaluating all rules for each content
unit that arrives".
[GA] Repeating a fragment that contains <head/> or <styling/> is expected in
a streaming delivery scenario. This would be required in general in order to
interpret any fragment that has a semantic dependency on <head/> or <tt/>.
Exactly, and that is true for referential styling too!
Another, and more primary reason for not including rule based styling in
DFXP is that the WG made a conscious choice to simplify DFXP, particularly
since the expected mechanism to be used for applicative styling will be the
use of XPath expressions to select the content to which styles will apply.
The use of XPath necessitates, in the general case, that the entire document
is memory resident in order to construct complex predicates.
Obviously a decision was taken by the WG, my point is whether it was the
correct one ;-)
I understand the restriction created by the use of XPath, and also see the
greatly increased complexity its use will allow in document instances. It is
unlikely that practical inserters will be developed IMHO to process AFXP to
true on-the-wire distribution format - this is what DFXP was intended for.
For my marketplace AFXP is of little relevance, the workstation product will
always be custom to the role of subtitling - I see little to be gained by
adopting the extreme sophistication allowed by AFXP in a preparation
workstation, only to throw most of it away in the transition to DFXP. My
interest is in a distribution format that solves some of the interchange
problems that are faced now by the marketplace. If DFXP does not contain
features that provide improvement over existing formats, what will prompt
it's adoption over those formats? If you are suggesting that distribution be
performed using AFXP (or a sub-profile of it), for what is currently the
largest single target for DFXP (subtitling), then what future is there for
DFXP?
The WG rejected the use of a non-general, special case mode of application
such as you suggest, preferring instead to support a general approach in
AFXP.
I don't see rule based styling as non-general or special case - it's a
powerful feature of CSS.
I am not personally convinced that this is more onerous than supporting a
referential style... YMMV !
Speaking as an implementor, I can assure you that it is more simple to
implement referential styling.
Hmmm! I was also speaking as a potential implementor. Why do you think
searching for an applicable rule is more difficult than searching for an
applicable style reference?
Not including this feature in DFXP does make restyling of DFXP content
somewhat more onerous.... since any relationship between a role and a style
will be lost by transition into DFXP. Consequently, this mandates the use of
AFXP for exchange and pre-distribution storage if the intention is to
support these relatively minor 'presentation' changes at output time.
If you examine the TTAF System Model in Figure 1, you will see there is a
compilation step when going from general AFXP to DFXP. Compilation usually
involves a loss of abstraction, in order to construct a simpler equivalent
expression. This is the model followed with DFXP.
Yet this is more than a loss of abstraction, it is a real loss of data. The
relationship between the style and the metadata is lost.
I may seem to be 'pedantic' on this point, but one of the major limitations
of existing formats is that they do not support easy transitions between
real on the wire distribution formats - where the distribution formats do
not provide equivalent support for presentation options - simply because
they also do not convey this connection between style and role. If there is
no connection between the role / agent metadata and the style in DFXP - then
there is little point in including the role and agent metadata IMHO.
There is no normative use of role/agent in DFXP; it was included to permit
passing through this metadata from AFXP for use by non-standardized
processing, or potentially future standardize processing. An AFXP to DFXP
compiler is free to not include this metadata in DFXP. However, it is there
in order to permit an author to interchange it on an end-to-end basis.
Yes, I understand. But exchange between **authors** should be at an AFXP
level surely? DFXP is targeted to support conversion into multiple true
distribution output formats. This one to many relationship requires that the
one format (the source) contains a sufficient richness, or a sufficiently
high level of abstraction to support the variations in output formats, but
still retain the original intention of the author. The intention of the
author (in subtitling at least) is NOT that a particular word be red, or
italicised, but that it be different from the surrounding context. Or put
another way, what is important is not **THAT** the style exists, but **WHY**
the style change exists. Further, there are very fixed conventions as to the
styling used to represent different contexts (dialogue, shouting, sound
effects, music), and those conventions differ from true on-the-wire
distribution format to format - and from user to user! But these conventions
exist for the same purpose, regardless of distribution format, and it is
that **purpose** that needs to be preserved (and IMHO enforced) in DFXP.
My concern Glenn is this.
Once you make the context optional, you effectively have thrown it away.
Without a strong emphasis on the relationship between style and 'role', DFXP
seems to be heading in a direction that (almost) encourages the development
of 'cooked' documents. IMHO this is the antithesis of what is required in a
true multi-target distribution format. I would personally dare to suggest
that DFXP should drop inline style and style references **totally**, in
favour of ONLY a class based style mechanism - simply to enforce the
relationship between style and context/role.
This is because in order to support the conversions that would be
anticipated, the style mechanism would have to also carry the role aspect as
part of the style ID.... thus creating an explosion in style definitions.
Further, each fragment of content that required identification would need to
carry a style reference.
Summary.
IMHO In this aspect, DFXP is too cooked. I prefer mine raw!
Then please contribute and support the development of AFXP.
I intend to, but I'm not so interested as to fund joining the W3C out of my
own pocket ;-)
BTW - Where does this streaming issue come from, a DFXP file is likely to be
trivial in size compared to ANY companion stream. (e.g. video or audio). I
would suggest that any composite stream that included a TT content stream
would simply do so by reference and require the target to pull down the
entire file.
regards John Birch.
-----Original Message-----
From: Glenn A. Adams [mailto:gadams@xfsi.com]
Sent: 17 March 2005 14:02
To: Johnb@screen.subtitling.com; public-tt@w3.org
Subject: RE: Timed Text Authoring Format - Distribution Format Exchange Pr
ofile (DFXP)
Actually, DFXP does not support out-of-line styling in the traditional sense
(e.g., CSS sense). The fact that one can place style specifications in
<head/> and share their use among multiple content elements is merely an
optimization of expressing inline styles (by reference). We call this
referential styling.
What you are requesting is a form of rule based applicative styling that
applies independent style rules to content based on matching criteria. This
mechanism will be defined in AFXP, but was explicitly ruled out for DFXP
since it requires either (1) having all content available to apply rules to,
or (2) repeatedly re-evaluating all rules for each content unit that arrives
(e.g., in a streaming scenario).
The basic model for DFXP is completely inlined styles, but the referential
styles were defined as an optimization to allow:
(1) aggregation and sharing of common inline styles
(2) pre-delivery or separate packaging of a fragment containing
referential styles from fragments containing content
The decision to simplify DFXP was based on the desire that DFXP content be
more concrete and directly parsable/renderable in a potential streaming
context. The general use of out-of-line applicative style rules is
antithetical to this approach.
G.
_____
From: Johnb@screen.subtitling.com [mailto:Johnb@screen.subtitling.com]
Sent: Thursday, March 17, 2005 7:56 AM
To: public-tt@w3.org
Subject: RE: Timed Text Authoring Format - Distribution Format Exchange Pr
ofile (DFXP)
Glenn, et al,
The DXFP specification includes support for styling, both in-line and
out-of-line styling.
However it does not support a class based styling model.
In subtitling, styles are most often associated with changes in the text
'role' (e.g. dialogue differs in presentation from music) or 'speaker' (Joe
- red, Frank - blue).
Could a mechanism be added to support this?
E.g. This might be represented in DXFP by utilising a class based style
mechanism that was sensitive to ttm:role and ttm:agent. Thus:
<style id="s1" style tts:color="white" tts:fontFamily="monospace-serif"/>
<style id="intro" style="s1" tts:fontSize="4%"/>
<style id="documentary" style="s1" tts:fontSize="10%"
tts:fontFamily="sans-serif"/>
<style id="music" ttm:role="music" tts:fontStyle="oblique"/>
<style id="joe" ttm:agent="joe" tts:color="red"/>
<div style="intro">
<!-- all text 4% high -->
<!-- all text monospace-serif -->
<p ttm:role="music">Quiet Violin music</p>
</div>
<div style="documentary">
<!-- all text 5% high -->
<!-- all text sans-serif -->
<p>White Large sans-serif</p>
<p ttm:role="music">White Oblique Large sans-serif</p>
<p ttm:agent="joe">Red Large sans-serif</p>
</div>
the ttm:role and ttm:agent attributes could be considered as implicitly
adding inline style attribute(s) to their container....
regards
John Birch
Senior Software Engineer,
Screen Subtitling Systems Limited,
The Old Rectory, Claydon Church Lane,
Claydon, Ipswich, Suffolk.
IP6 OEQ
Tel: +44 1473 831700
Fax:+44 1473 830078
www.screen.subtitling.com
See us at NAB Las Vegas April 18-21st Stand No. SU8956
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-----Original Message-----
From: Glenn A. Adams [ mailto:gadams@xfsi.com <mailto:gadams@xfsi.com> ]
Sent: 14 March 2005 16:51
To: public-tt@w3.org
Subject: Timed Text Authoring Format - Distribution Format Exchange
Profile (DFXP)
A new update of the Timed Text Authoring Format 1.0 - Distribution
Format Exchange Profile (DFXP), is now available at [1]:
http://www.w3.org/TR/2005/WD-ttaf1-dfxp-20050314/
<http://www.w3.org/TR/2005/WD-ttaf1-dfxp-20050314/>
The TT WG solicits your comments on this new draft as soon as possible,
as a very rapid turn-around is expected in order to publish a first Last
Call (LC) draft.
Please sent comments either to this list or, if you prefer privacy, to
me directly.
Regards,
Glenn Adams
Received on Thursday, 17 March 2005 17:17:26 UTC