- From: Erik Hodge <ehodge@real.com>
- Date: Thu, 30 Jan 2003 10:10:17 -0800
- To: "Glenn A. Adams" <glenn@xfsi.com>, "W3C TT Public" <public-tt@w3.org>
At 08:22 PM 1/29/2003 -0500, Glenn A. Adams wrote: >I should have added the following: > >In using RealText and QuickText as (potential) examples of non-streaming >TT content, I did not mean to imply that they were only non-streaming; I >believe (but am not completely certain) that they also may be delivered >in streaming mode; perhaps someone can confirm this for me. RealText was conceived in late 1996 precisely for streaming of long- format text. Its predominant use, however, is just to add short, non-changing text to presentations, e.g., a title, a caption, or a seekable table of contents. But, I've seen a 4 Megabyte RealText file streamed along with a 6-hour video presentation. The RealText *file format* was designed to be independent of delivery method, and to be easily packaged for just-in-time delivery. It's up to a file-format handler on the server side to decide how to package and deliver the contents of the text based on the delivery environment. The *wire format* I think is what we probably don't want to define for TT, but we certainly should think about it while designing the *file format*. So, to be "streamable", a file format should be designed so that: (a) the file handler (reader, parser, packager) on a server (or on the client if HTTP or local-file) doesn't have to read/parse/store the entire file in order to determine what needs to be sent at any given time. (b) the file handler can easily handle a seek request to any given time in the stream with a minimal use of server-side resources. The implications of this include: (1) An XML (assuming we choose that) file can't be validated without reading/parsing the entire file. Therefore, the file has to already be assured to be valid, well-formed XML before an attempt to stream it is made. RealText just does its best when confronted with XML errors without throwing an error and/or stopping the presentation. (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. - Erik >G.
Received on Thursday, 30 January 2003 13:03:13 UTC