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Timed Text (TT) Authoring Format 1.0 Use Cases and Requirements - Comments!

From: <Johnb@screen.subtitling.com>
Date: Fri, 16 May 2003 10:35:10 +0100
Message-ID: <11E58A66B922D511AFB600A0244A722E093FC0@NTMAIL>
To: public-tt@w3.org
Dear TTWG,
I have just read the draft document Timed Text (TT) Authoring Format 1.0 Use
Cases and Requirements - very clear and comprehensive.
Please find below some comments.
Note in all my comments you may freely substitute caption* for subtitl*  !

RE: Issue (I002):
>Should block level graphics be supported, e.g., to permit pre-rasterization
of entire lines or blocks of lines of text to serve as alternate content?
For example, some subtitling systems use pre-rasterized text that are
represented as bitmap graphics.
It is certainly true that **some** subtitling systems use pre-rasterised
text. This is recognised within subtitling as having distinct
A: Self-evidently pre-rasterised text precludes the ability to **easily**
modify and qualify subtitle files after they have been produced by the
B: Pre-rasterised text requires a greater bandwidth/storage capacity than
existing file formats used to code subtitles.
C: Pre-rasterised text does not scale well.
D: Pre-rasterised text imposes 'producer' choices on the 'consumer' - this
may contradict with the required 'house styles' used by consumer.
There are some advantages: (some of which perversely are the inverse of the
A: Pre-rasterised text imposes a certain protection on subtitle files,
potentially requiring that changes are performed only by a suitably equipped
B: Pre-rasterised text may be previewed by a more simple common viewer
C: Pre-rasterised text may allow for more sophisticated text effects and
styles that cannot be easily produced 'in real time' at a later stage in the
subtitling chain. E.g. 3D glyphs, metallic surfaces and textures...
D: Pre-rasterised text avoids the 'consumer' detrimentally altering the
subtitles (e.g. by selecting too large or small a font) - there is a clear
responsibility for poor subtitles.
While I would not advocate excluding pre-rasterised text - I would advocate
that pre-rasterised text ONLY occurs in a TTAF together with a non
pre-rasterised form. Further I do not like the term alternate content - as
to me it implies that the pre-rasterised form is the 'second' choice - this
may not be the intention of the author / user. Surely pre-rasterised text is
still text?
RE: R502 - Highlight Animation:
>The TT AF shall be capable of expressing animated highlighting of content,
with granularity at the level of individual characters or glyphs.
The list of animated style parameters is some what restrictive IMHO - being
limited to colour changes, visibility and position. Certainly for Karaoke I
would suggest that the ability to decorate text (by underline - floating dot
etc) might be desirable. Other desirable possibilities for highlighting
might include changes to text emphasis (e.g. bold) or even font style /
family. One characteristic of highlighting is that it should not IMHO alter
the text flow, that is any highlighting of text content should not affect
the position of **any** currently displayed glyphs during highlighting.
RE: Issue (I005):
>The rights (accessrights) metadata item defined by [DCMES 1.1]
<http://www.w3.org/TR/2003/WD-tt-af-1-0-req-20030515/> has not been included
here, pending further consideration of whether and what intellectual
property rights management (IPRM) related metadata to explicitly support in
the TT AF.

The inclusion of some form of rights and accessrights information is IMHO
very important. Also of concern is the need to protect the intellectual
property of the content. Speaking only wrt subtitle files - these are costly
to produce - and many users regard a subtitle file as a significant asset.
The inclusion of rights metadata does not protect the content from
unscrupulous exploitation. Is there a means by which the content of the file
(by which I mean the Timing / Style and Text) might be encrypted - whilst
leaving the metadata in the clear?


John Birch
Senior Software Engineer
Screen Subtitling Systems  
The Old Rectory, Church Lane
Claydon, Ipswich, Suffolk
The views and opinions expressed are the author's own and do not necessarily
reflect the views and opinions of Screen Subtitling Systems Limited.
Received on Friday, 16 May 2003 05:31:30 UTC

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