WebTV Interactive TV

You may remember the hype surrounding Interactive TV (ITV) back in the early 1990s that barely made it to field testing before it died. Well Interactive TV is back in the form of convergence between the web and TV and WebTV is leading the way with a new standard.

The WebTV Plus box has been out for about a year and includes the new Interactive TV functionality, the original WebTV, which is still available, does not include Interactive TV. In addition to the ITV content, the WebTV Plus box also supports Macromedia’s Flash 2.0, Real Audio 3, Javascript and a very limited implementation of Dynamic HTML. Java and the newer versions of Real Video/Audio are not supported.

In addition to delivering ITV content to Web TV Plus, Microsoft has also included ITV in Windows 98 with "WebTV for Windows 98". This feature is latent in Win98 and will only become available when you install a TV Tuner card.

Vertical Blanking Interval and Crossover Links

Mixing web and TV content starts with the broadcaster of the TV signal. The URL and other information is encoded into the broadcast signal in the Vertical Blanking Interval (VBI). This is the same part of the broadcast frequency that carries the Closed Caption information. The WebTV plus box interprets this signal and when it is received places an icon (see below) in the upper right corner of the TV screen. This link is called a "crossover" link.

When this is clicked on the user is taken to a web page that combines web and TV content.

For those of you without a broadcast TV station there is a way to create ITV content. The crossover link can also be embedded in a regular web page. The link uses the following code:

<a href="crossover_beta.html" view="tv">Link to Cross Over Example</a>

This link would jump you to an ITV page where you can have mixed web and TV content. The view="tv" is the critical part of making sure the WebTV Plus box knows it can start using ITV content.

Embedding and Overlaying with the TV Signal

The Web and TV content can be mixed together in two ways.

  1. A web page can overlay the video signal so that the web page floats over a full screen TV signal
  2. The TV signal can be embedded in the page like a graphic and take up only a small part of the page.

Let’s look at the code to accomplish these two options. Remember the page in which you implement this code must have been linked to using the view="tv" link.

Overlaying Code:

The TV image simply becomes the body background in the HTML, in this case Channel 49 is shown:

<body background="tv:49">

Then the rest of the web page gets built on top of the video signal. An example of this can be seen here. This will only look proper on a WebTV Plus box.

Embedding Code:

The video signal can also be used to make up an object on the page. It can be used much like a JPG or GIF file is placed in the page. Several methods can be used for this, both have the same result. An example can be seen here.

If you embed the TV signal as an object:

<embed height=305 width=476 src="tv:49">

If you embed the TV signal as an image:

<img src="tv:49" height=305 width=476 border="0">

If you are in the "TV World" using ITV the web pages become non scrollable so they must be designed to fit on the screen all at one time. If you want to jump back to the "Web World" to view normal web pages you can use the code:

<a href="normal_web_page.html" view="web">Link back to Web</a>

WebTV has done a great job of easily integrating the TV signal into web pages. Instead of creating a proprietary development platform they have also made good use of web standards in order to implement Interactive TV. WebTV will soon be moving to Windows CE and with this development platform they should be able make the idea of convergence a reality.

Jeff Rule is a principal at RuleWeb Development specializing in DHTML, SMIL, Shockwave and Java based multimedia enhancements for advanced media sites. His first book, Dynamic HTML: The HTML Developer's Guide will be published in November 1998 by Addison Wesley Longman. It features many DHTML multimedia examples from his popular DHTML Demo's web site.


Sidebar 1

The Vertical Blanking Interval contains the following information:





The web site address of the interactive TV content.



A way to categorize interactive television links.

Program, Network, Station


The catchy or interesting message viewers see.

ABC Nightly News


Enables the use of interactive TV links to trigger javascript functions



Specifies the last date the interactive TV link is valid



The view attribute specifies how the receiver should display the linked resource



Shortening of common names

[type:sponsor] becomes [t:s]


Verifies the accuracy of the string and detects data corruption.