RE: TT and subtitling/captioning - separating timing from style from content - temporal flow of content

See below.


  _____  

	From: Johnb@screen.subtitling.com [mailto:Johnb@screen.subtitling.com] 
	Sent: Thursday, August 07, 2003 6:44 AM
	To: public-tt@w3.org
	
	

	Dear TT-WG, 

	For those that don't know me -  I am a software engineer for a company that produces subtitling (captioning) equipment 
	- so all my comments should be taken in that context. 

	I have just been reading through the F2F minutes for March on the TT-WG home page, 
	and have two questions regarding the tentative model that seems to be appearing for TT-AF. 

	Assuming that I wish to separate the timing in my TT-AF document from the content 
	- by using references within the timing 'tree' a la Daisy model - and assuming that this might be possible! 
	- would it then possible to apply style through the timing tree rather than by inline markup or attribute within the text content.

	I.e. - using example (crudely hatcheted from GA examples) 

	<seq> 
	<ref id="T27" dur="3s"/> 
	<ref id="T28" begin="T27.end " dur="3s"/> 
	</seq>  

	If we support this idiom, then we would introduce a new element type cue instead of using the SMIL ref element type. It would take a select attribute that would use XPointer or XPath to select the content. Also, your use of the begin attribute above is redundant, since the semantics of seq imply that subsequent children follow immediately in time.

	<tt:content id="T27"> 
	 Some text with some&nl; Hard line breaks. 
	</tt:content>  

	We wouldn't use &nl; for a forced line break, but instead use an empty element, e.g., <br/>, or use a style break-after: line. 

	<tt:content id="T28"> 
	 Some more text with some&nl; Hard line breaks. 
	</tt:content> 

	will it be possible to do something like this.... (in spirit if not in exactly this manner...)? 

	<seq> 
	<ref id="T27" dur="3s" style="text-indent:10pt"/> 
	<ref id="T28" begin="T27.end " dur="3s" style="font-size:14pt"/> 
	</seq>    

	This could be readily supported using SMIL/SVG animation vocabulary, e.g., the above would read as (using cue instead of ref as described above):

	<seq>
	  <cue select="id(T27)" dur="3s">
	    <set attributeName="text-indent" to="10pt"/>
	  </cue>
	  <cue select="id(T28)" dur="3s">
	    <set attributeName="font-style" to="14pt"/>
	  </cue>
	</seq>

	<tt:content id="T27"> 
	 Some text with some&nl; Hard line breaks. 
	</tt:content> 

	<tt:content id="T28"> 
	 Some more text with no Hard line breaks. 
	</tt:content> 

	further - might it be possible to replace the style attribute above 
	with a reference to an element (or portion of a style sheet) 
	that defines the style (to avoid multiple large style attribute definitions)? E.g. 

	<seq> 
	<ref id="T27" dur="3s" style="S1"/> 
	<ref id="T28" begin="T27.end " dur="3s" style="S2"/> 
	</seq> 

	<tt:content id="T27"> 
	 Some text with some&nl; Hard line breaks. 
	</tt:content> 

	<tt:content id="T28"> 
	 Some more text with no Hard line breaks. 
	</tt:content> 

	<StyleDef id="S1" defn="text-indent:10pt"/> 
	<StyleDef id="S2" defn="font-size:14pt"/>  

	This could be accomplished by declaring the animation elements separately, and then referring to them for reuse. This would essentially be syntactic sugar, but I would guess useful, at least in terms of saving typing and DOM footprint, e.g., the above example might be expressed as:

	 

	<animations>
	  <animation id="a1">
	    <set attributeName="text-indent" to="10pt"/>
	  </animation>
	  <animation id="a2">
	    <set attributeName="font-style" to="14pt"/>
	  </animation>
	</animations>
	<timing>
	  <seq>
	    <cue select="id(T27)" dur="3s" use="a1"/>
	    <cue select="id(T28)" dur="3s" use="a2">
	  </seq>
	</timing>

	A second question.... 

	It would be desirable for TT (at least IMHO) to include mechanisms for describing the temporal breaking of content. 
	What I am thinking of is a document that does not describe explicitly the timing for all of the content 
	- but rather describes that X amount of content fits into a box of size Y over a time period of Z. 
	Now if the content X is too large for box Y - how does the content get over(?)flowed in a 'temporal sense' through the box.  

	I'm not sure I'm following your scenario here. Are you saying you want individual characters, words, lines, etc. to appear in box Y over time, and do so without explicitly timing each unit? If so, I can see some possible problems, such as (1) needing to specify the granularity of content to be timed (i.e., character, word, etc.); (2) which would entail the need to formally specify how to subdivide content lacking markup into such units. While this might make the content of a TT-AF file smaller, it would also be possible to do this by animating the visibility property of individual units explicitly, making decisions about what constitute units at authoring time, e.g.,

	<style>
	  span { visibility : hidden }
	</style>
	...
	<animation id="a1">
	  <set attributeName="visibility" to="visible">
	</animation>
	...
	<par>
	  <cue begin="0s" select="w1" use="a1"/>
	  <cue begin="3s" select="w2" use="a1"/>
	  <cue begin="6s" select="w3" use="a1"/>
	</par>
	...
	<p>
	  <span id="w1">word1</span>
	  <span id="w2">word2</span>
	  <span id="w3">word3</span>
	</p>

	This would work whether or not you expecify forced line breaks in content using <br/> or break-after:line. Note that the visibiliy property doesn't affect line breaking or layout, but only the visibility of the layed out content.

	This is a 'crux' issue in subtitling / captioning. 

	regards 
	John Birch 

	The views and opinions expressed are the author's own and do not necessarily 
	reflect the views and opinions of Screen Subtitling Systems Limited.