W3C home > Mailing lists > Public > public-tt@w3.org > January 2003

RE: TT Content Buffering and Timing Scenarios

From: Erik Hodge <ehodge@real.com>
Date: Thu, 30 Jan 2003 12:41:38 -0800
Message-Id: <>
To: "Glenn A. Adams" <glenn@xfsi.com>
Cc: "W3C TT Public" <public-tt@w3.org>

At 01:16 PM 1/30/2003 -0500, Glenn A. Adams wrote:

>Could you describe some of the issues with "live timed text" more
>fully and how it can "never have XML rules enforced"? Are you
>saying that even well-formedness rules aren't possible?

(I wrote the following before seeing your response about having
each "access unit" be a self-contained XML document.  I'm
sending this anyway as it may help clarify the problem to

It's not that the rules aren't possible to apply, it's that you
can't verify that it is or is not well-formed until after you've
seen the entire stream.

Here's an example of where an "ill-formed" XML data stream would
not be detectable until after it starts (but you certainly could
detect it and throw an error if you wanted to):

Let's say the live stream is coming from a computer on which someone
is typing some speaker's words and transmitting each sentence as soon
as it is typed.
(1) At time zero they type, "<moderator><strong>Good evening.
Welcome to the Food Show."  This then gets sent (streamed) at 6s.
(2) At 6 seconds they type, "Tonight we will be discussing which
wines go best with different snack foods." This gets sent at 14s.
(3) At 14 seconds they type, "With me today are Phillip McGlass,
editor of Wine About Magazine, and Don Nutt, editor of Junk Food
Magazine</moderator>", which gets sent at 23 seconds.

As you can see, the XML data stream fails to be well-formed at 23
seconds when "</moderator>" is sent without a "</strong>" preceding
it.  Now, the system could react by:
(1) throwing an error and stopping the stream
(2) ignoring the error and maintaining the subsequent text as
(3) ignoring the error and inserting a </strong> into the
appropriate place in the stream to force it to be well-formed.

None of these options is ideal.

         - Erik

> > -----Original Message-----
> > From: Erik Hodge [mailto:ehodge@real.com]
> > Sent: Thursday, January 30, 2003 1:10 PM
> > To: Glenn A. Adams; W3C TT Public
> > Subject: RE: TT Content Buffering and Timing Scenarios
> >
> > (2) Live (created-on-the-fly) timed text can never have XML rules
> > enforced because the entire file doesn't even exist when it starts
> > to be shown.  Live RealText provided me with a lot of challenges
> > in other ways as well.
Received on Thursday, 30 January 2003 15:34:43 UTC

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