Liberate TV Navigator (TV Set-top Box)

An interactive TV set-top box environment.

This is possibly the most advanced of the TV set top boxes that provide a 'Browser in a box'.

This system is gaining much popularity in the UK and Europe and is also becoming more prevalent in the United States. It has the backing of several very large players in the digital TV market and was founded as a joint venture between Netscape Communications and Oracle Inc.

Broadcast head end systems are generally built on Unix systems. Since the heritage of Liberate is that of the Netscape browser, the Liberate platform relates to the Microsoft TV platform in much the same way as the Netscape browser does to the MSIE browser.

From the consumer's point of view, one of the benefits of the Digital TV revolution is that generally the set-top boxes are supplied by the broadcasters. The broadcaster already has control over what gets transmitted from the head end and can now control how it is received. Although we have competing standards for set-top boxes, a TV set-top box will generally receive a predictable content model from the broadcast headend.

The Liberate platform does all that the WebTV and Microsoft TV platform does and possibly more besides, although both are competing with one another and raising the stakes all the time, just like it was during the 'Browser Wars'.

For example, you can request content from an ISP via a dial-up connection or from an always-on cable modem. This uses the normal HTTP request method. However, you can also request resources from the in-band broadcast video signal. These are done with additional request methods. These will allow you to request an item from a particular carousel. A carousel is a collection of assets that are transmitted in a cyclic manner and are embedded into the digital TV transport stream. Requesting an item from a carousel is no more complicated than requesting it from a web server. When the object is delivered on the next carousel cycle it is displayed by the browser in the normal way. Pages can be constructed with any mixture of in-band or online content.

Carousels can be associated with a particular channel or can be shared by many channels being broadcast on a digital TV multiplex.

This platform works very well in Digital Satellite (DSat), Digital Cable (DCable) and Digital Terrestrial (DTT) systems, although at this time it is becoming very popular on DCable.

The present version of Liberate in wide circulation is 1.1 and it is in the process of being upgraded to 1.2. The upgrade process is accomplished by downloading a new browser core into the set-top box which then updates its persistent Flash ROM.

Liberate 1.2 supports much enhanced carousel delivery, ATVEF triggers and also some basic Flash animation support. The JavaScript support is basically 1.2 and the HTML is based on version 3.2, which poses some difficulties in achieving the display effects people are used to deploying with HTML 4. These limitations are imposed because the set-top box hardware is based on a cost-limited CPU which has limited memory and performance. This is necessary to be able to deploy the boxes at a cost that is commercially viable.

As the cost/performance ratio improves, boxes will become more capable and support higher level functionality. It is likely that the Flash support for example will receive some considerable attention, because it allows the designers of the program related material to achieve more advanced and animated effects.

The JavaScript functionality has a few limiting factors when compared with the Netscape browser used in a PC. This extends to a few objects and methods being unavailable. However, there are additional TV-related objects and methods that provide the control of channel switching, volume control and TV overlays. You can for example use HTML to design a semi-transparent overlay that is placed on top of the video or you can place the window into a web page so it resembles an embedded video player plugin.

Major Cable operators and AOL TV are among the services offering contents that work with the Liberate platform.

See also:ATVEF, Interpret, TV Set-top boxes