RE: TT and subtitling

Re: difference in access and presentation units, it would depend
upon how the latter is defined. For example, if defined as the
bitmap to be BLTed into a graphics plane, then if the access
unit were that bitmap, there would not be a difference; however,
if the access unit were a compressed image, e.g., JPEG, PNG,
etc., then there would be a non-zero decoding time. Further,
but if the access unit were text which required layout and
glyph rasterization, then there would be a fair difference,
and non-zero decoding time as well.
 
G.

	-----Original Message-----
	From: Johnb@screen.subtitling.com [mailto:Johnb@screen.subtitling.com] 
	Sent: Monday, February 03, 2003 5:06 AM
	To: Glenn A. Adams
	Cc: public-tt@w3.org
	Subject: RE: TT and subtitling
	
	

	GAA> 

		As for access unit vs presentation unit, I would tend to use the
		former when talking about the coded representation and its delivery
		and buffering modes, and use the latter term for talking about its
		decoded to-be or currently presented modes. 

	I must admit I find this a sublte distinction - do you anticipate there being a major difference between the format of an access unit and a presentation unit for TT? (encryption and compression issues aside).