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RE: Timed Text Authoring Format - Distribution Format Exchange Pr ofile (DFXP)

From: Glenn A. Adams <gadams@xfsi.com>
Date: Sat, 19 Mar 2005 18:17:18 -0500
Message-ID: <7249D02C4D2DFD4D80F2E040E8CAF37C0E9049@longxuyen.xfsi.com>
To: "Sean Hayes" <shayes@microsoft.com>, <Johnb@screen.subtitling.com>
Cc: <public-tt@w3.org>
While it is true that one could divide fragments into separate document
instances, that is not what I had in mind. I had in mind the proven work
of MPEG-7 Part 1 with its definition of BiM, or a similar type of
fragment encoding. The effort to use this type of mechanism is minimal
while the gain is significant. Note that this mechansim has also been
adopted by TV Anytime for unidirectional delivery of metadata.

 

  _____  

From: Sean Hayes [mailto:shayes@microsoft.com] 
Sent: Saturday, March 19, 2005 6:01 PM
To: Glenn A. Adams; Johnb@screen.subtitling.com
Cc: public-tt@w3.org
Subject: RE: Timed Text Authoring Format - Distribution Format Exchange
Pr ofile (DFXP)

 

Right, I didn't say it was impossible, just that it seems like a lot of
effort for not much gain. You could for example do <f0,f1-f4> as one
dfxp instance, and <f0,f5-9> etc as other document instances. The
granularity can be chosen to match the delivery scenario.

 

  _____  

From: Glenn A. Adams [mailto:gadams@xfsi.com] 
Sent: 19 March 2005 03:47
To: Johnb@screen.subtitling.com; Sean Hayes
Cc: public-tt@w3.org
Subject: RE: Timed Text Authoring Format - Distribution Format Exchange
Pr ofile (DFXP)

 

See http://www.w3.org/TR/2005/WD-ttaf1-dfxp-20050314/#streaming for a
prelimiinary discussion of streaming DFXP content, where data access
units are XML or infoset fragments of a DFXP document instance.

 

G.

 

  _____  

From: Johnb@screen.subtitling.com [mailto:Johnb@screen.subtitling.com] 
Sent: Friday, March 18, 2005 6:16 AM
To: shayes@microsoft.com
Cc: public-tt@w3.org
Subject: RE: Timed Text Authoring Format - Distribution Format Exchange
Pr ofile (DFXP)

 

Sean,

 

Welcome aboard the thread!

 

[SH]

I've never really accepted that streaming a single XML document is a
particularly likely scenario. Much more likely IMO is to break the
captions up into 'I-frame' mini documents which stretch for a
significant period of time (e.g. a DVD chapter) and if necessary repeat
these on a cyclic basis in a media stream.

[JB]

An interesting idea.... I've only thought about this from each extreme,
i.e. streaming per subtitle (and periodically sending a header), or
sending the whole document. If I understand correctly you are suggesting
chopping a large DFXP document into multiple smaller ones? Each valid in
itself? This is certainly compatible with Digital Cinema thinking, where
a very large media file is chopped into 'reels'. 

 

[SH]

I think it is likely that if and when AFXP is made available that it, or
more likely a constrained use of it (effectively another profile), will
be more useful as a modern captioning and subtitle technology.

[JB]

Yes, I absolutely agree. Problem is the pressure is on to adopt
something now!. Maybe the 'path' is to adopt DFXP on the understanding
of allowing a constrained superset of DFXP (or AFXP sub-profile) in the
future, to cater for re-work scenarios.

 

best regards

 

John Birch

 

 -----Original Message-----
From: Sean Hayes [mailto:shayes@microsoft.com]
Sent: 18 March 2005 10:30
To: Glenn A. Adams; Johnb@screen.subtitling.com; public-tt@w3.org
Subject: RE: Timed Text Authoring Format - Distribution Format Exchange
Pr ofile (DFXP)

	I'm just catching up on this thread. I must admit that I share
John's opinion that not supporting applicative styling in DFXP is
probably an error, and I have said so on numerous occasions in the WG,
however I have given in to the majority opinion (on the understanding
that this feature goes into AFXP). I do accept it would mean a
significant increase in overhead for DFXP, but in my opinion not so much
that makes it impractical. 

	 

	What is probably more significant at this stage is that adding
it will delay the already well overdue DFXP document.

	 

	I've never really accepted that streaming a single XML document
is a particularly likely scenario. Much more likely IMO is to break the
captions up into 'I-frame' mini documents which stretch for a
significant period of time (e.g. a DVD chapter) and if necessary repeat
these on a cyclic basis in a media stream.

	I think it is likely that if and when AFXP is made available
that it, or more likely a constrained use of it (effectively another
profile), will be more useful as a modern captioning and subtitle
technology.

	 

	Sean

	 

	
  _____  


	From: public-tt-request@w3.org [mailto:public-tt-request@w3.org]
On Behalf Of Glenn A. Adams
	Sent: 17 March 2005 09:56
	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 12:33 PM
	To: public-tt@w3.org
	Subject: RE: Timed Text Authoring Format - Distribution Format
Exchange Pr ofile (DFXP)

	 

	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!

		 

		[GA] Yes. This is understood, and is acceptable (and
different from the general model).

		 

		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? 

		 

		[GA] Clearly, the WG members believe that DFXP is more
than adequate to serve as an interchange format among existing
distribution formats. If you can present a concrete case why this is not
true, then I'm certain the WG will carefully consider. Also, keep in
mind that you can use arbitrary extensions in DFXP provided they are in
a different namespace. This will allow you and others to customize their
uses. If it appears that there is a common extension desired by many
parties, then we can consider standardization.

		 

		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.

		 

		[GA] And it will be similarly powerful in AFXP, but not
DFXP.

		 

		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?

		 

		[GA] Because looking up a referential style does not
require traversing the document instance. It merely requires a hashtable
lookup on the set of styles already received in the fragment that
contains the <styling/> element. In contrast, applicative styling
potentially requires evaluating every node of the DOM in order to match
a single rule.

		 

		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.

		 

		[GA] What you call "data" I call "abstraction". It does
not lose "content". Furthermore, if a compiler wishes to do so, it can
add non-standardized decorations that allows it to recover the
abstraction. However, standardization of such reversible transform is
not a requirement for DFXP, and, indeed, was an explicit
non-requirement.

		 

		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?

		 

		[GA] It is not the intent of the WG or its specs to
dictate to authors how they should use the different profiles. It is
their choice. The two profiles have different design centers. DFXP is
explicitly intended to be cooked/flattened/compiled...

		 

		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.

		 

		[GA] Then you will want to use AFXP for such abstraction
level, or add proprietary extensions to DFXP.

		 

		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.

		 

		[GA] I'm afraid you have a different idea of the
intention of DFXP than the TT WG. The intention you ascribe to DFXP is
what the TT WG ascribes to AFXP.

		 

		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 ;-)

		 

		[GA] Then you will have to be satisfied with what the TT
WG produces, while, of course, taking due consideration of yours and
other comments from the public. I would note that some very small
companies (mine for instance) is willing to make this investment out of
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.

		 

		[GA] There are many real-world use cases where it would
be useful or important to integrate DFXP content into a streaming data
context, particularly in unidirectional delivery contexts.

		 

		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] 
			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/ 

			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 Saturday, 19 March 2005 23:17:15 GMT

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