Know Your Client Platform

Platform SDK: Broadcast Architecture

Know Your Client Platform

Each client platform that supports the ATVEF standard may interpret the standard in a slightly different way. By becoming familiar with the platform or platforms your client will be viewing the interactive show on, you can write an authoring tool that handles any inconsistencies.

The following section describes how the ATVEF standard is handled by the WebTV for Windows client.

ATVEF Enhancements on WebTV for Windows

The following lists ATVEF enhancement restrictions or recommendations specific to the WebTV for Windows client platform.

Create a base URL, and specify files relative to that base URL. A base URL is the same as a top-level page in the enhancement.
Do not use variable-length UHTTP packets, these are not handled by the WebTV for Windows client.
Do not transmit encrypted or compressed SAP/SDP announcements, these are not handled by the WebTV for Windows client.

Script transmitted in triggers is run relative to the top-level enhancement page. This page typically contains the implementation of any script functions called by triggers. The following ECMAScript examples illustrate how to navigate down to sub-elements of the base page using the DOM:

// Call a script named "writetime" in the frame named "trigger" 
// and pass the value "End of Show" to that script.
window.top.frames.trigger.writetime("End of Show")
 
// Change the background of page in the "main" frame. This is done
// by navigating down the DOM to the body tag on that page and
// setting its background color attribute to blue.
window.top.frames.main.document.body.style.backgroundColor="blue"
 
// Display "main.htm" in the frame named "main"
window.top.frames.main.location.href="main.htm"

For more information about ECMAScript syntax, see the specification at http://www.ecma.ch/stand/ecma-262.htm.

The Web TV for Windows client supports the use of tv: URLs within <OBJECT> and <EMBED> tags. It does not support the use of tv: URLs inside the following tags: <IMG>, <BODY>, <FRAMESET>, <A>, <DIV>, and <TABLE>.
When framesets are used, the tve-receiver object cannot be on the same page as the base URL. This is because the HTML specification declares that you can't include anything on the same page with a FRAMESET tag. (Note that on the WebTV for Windows client, the tve-receiver object is implemented as the Trigger Receiver control.)
The tve-ends attribute, which is optional in the ATVEF specification, is required by the WebTV for Windows client.
The WebTV for Windows client ignores the b=CT:<number> and a=tve-size:<KB> announcement fields