Interactive television is simply integrating active Web content with a television broadcast. Our platform and ATVEF{link to Interactive TV and ATVEF page, 2.1} define Web content as standard HTML and other Web elements. Since standard HTML does not take into account integrating a television broadcast, extensions were designed to existing tags to allow this combination.
Specifically, ATVEF defines an extension to the anchor tag called the view attribute. The view attribute has two valid values: Web and tv. When a TV browser receives a trigger with this attribute, it accepts that there may be some combination of Web and broadcast content. It must retrieve the HTML page to determine how that combination is implemented.
The view attribute can be used in a trigger that asks the home viewer if they wish to display the Web content (on our receivers, this shows up as a "Go Interactive" option). Or the view attribute can be used on a standard Web page to indicate that following a link switches the viewer from the Web world to the TV world.
Example:
<a href="http://webtv.net/" view=tv>
Within the "tv:" attribute you can reference a specific channel by a unique DNS-style identifier. This is especially important when placing a trigger in the Web world where you cannot be certain of the currently tuned channel. For example, the tag "tv:west.hbo.com" indicates the current program on the HBO West Coast broadcast feed. The empty tag "tv:" indicates that broadcast video should be displayed using the current TV tuner setting.
For specific details about the standard for using the "tv:" attribute, please refer to IETF specification Uniform Resource Identifiers for Television Broadcasts (RFC 2838).
As the receiver loads the HTML page it integrates the broadcast by one of two types of instruction: the broadcast image is either used as a background or it is inserted as an image or object within the confines of the Web page.
If you want the TV image to dominate the TV screen, complemented by Web content (for example, a transparent menu), you can make the TV image a background. To do so, use the "tv:" attribute in conjunction with the <BACKGROUND> tag.
The syntax is as follows:
<body background="tv:">
If you want a Web page to dominate the TV screen with the TV image occupying just a portion, then you might use one of the following examples that gives you more control over such attributes as size and position:
<img src= "tv:espn.com" height=90 width=120>
<object data= "tv:cnnfn.com" height=90 width=120>>
TV images can also be layered on top of Web pages, using z-ordered (three-dimensional) cascading style sheets. In this case, the video should be set to "Z= -1" to make it the bottom layer.
Example:
<div style="POSITION: ABSOLUTE; Z-INDEX:-1">
<object data="tv:" height=100% width=100%>
</object>
</div>
The "tv:" attribute can also be used to display a television channel without any Web page enhancement.
For example, if you include an <A HREF="tv:"> tag in your Web page, the current channel is tuned in and displayed as full-screen television. The problem with this is that you lose control over the viewer%u2019s attention if you send the user back to the TV world. It is best to use a blank page with the image as a background. That way you can provide a small icon or link in the corner if the user wants to return to your content.