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INTRODUCTION TO TECHNOLOGY

The Liberate TV Platform™ consists of the Liberate TV Navigator™ middleware solution for set-top boxes, and Liberate Connect™, a suite of server-based network solutions that deliver and manage interactive services to set-top boxes.

There are three versions of the TV Navigator middleware: Standard, Compact and Analog.

TV Navigator Standard is designed for mid range to high-end set-top boxes, such as the Motorola DCT-5000. The most recently announced version for the Standard Platform is version 1.3.

TV Navigator Compact, which currently runs exclusively on the Motorola DCT-2000, is available in two versions: v2.4, which is HTML-based with two-way communication (HTML is transcoded seamlessly into MPEG iFrames), and v3.0.10, which is Java-based with one-way, unidirectional, broadcast based communication. The Liberate Java implementation is called "microVM": it is a subset of Java applicable to this class of devices. Under the recent announcement between Liberate and Sun, this microVM will evolve in the future into a Sun approved CLDC profile, enabling "Java" branding. The current Upcoming versions of the Compact Platform are designed to support two-way communications (version 3.2).

TV Navigator Analog is the middleware used for AOLTV, which has also been licensed to Inprimis, a decoder hardware design company.

Liberate Connect is a modular suite of servers, including Command, Datapoint, Imprint, and Transcode (with its Security server). Liberate Transcode, a content translation server, is the component that has the most impact on the content developer. When deployed to support TV Navigator Standard, Liberate Transcode pre-processes HTML before delivering the content to the set-top box to clean syntax errors, transform the content MIME types into the MIME types supported by memory and CPU constrained set top boxes running the TV Navigator client. When supporting TV Navigator Compact, Liberate Transcode converts the HTML into a series of MPEG still frames. These stills are then stored in an MPEG carousel and are broadcast to the set-top box according to the user's input, creating an interactive experience.

Finally, the Liberate Mediacast server sends and inserts data and application into the MPEG inband stream, for delivery over the broadcast channel into the set top base.

For more information about content authoring for the Liberate TV Platform, please consult the Content Developer's Guides included in Liberate TV Producer and TV Producer Compact.

Rendering and resizing
Both Liberate TV Platforms automatically resize content to fit on the television screen, but their functionality is slightly different. The Compact Platform assumes a frame size of 640x416, renders the MPEG stills at the head end and uses the video decoder of the set-top box to display the content. The Liberate TV Platform Standard assumes a frame size of 560x420, and renders the post-transcoded content on the set top box.

For both platforms, the Liberate Transcode server will "correct" the content for TV display. For example, horizontal scrolling is not considered a "TV-like" property, so content is scaled to fit the horizontal screen dimensions. If more space is needed, vertical scrolling is enabled to allow the viewer to navigate the page. The transcoder will also automatically wrap text that extends outside a given frame's area. In the case of tables, the transcoder will ignore widths specified in HTML if the cell or the table is too wide to fit within the screen dimensions. The cells are adjusted based upon the content within the cells. Because these layout decisions are made by the Liberate Transcode server software, developers should test this functionality before deployment.

Color
The Liberate Transcode server changes colors for the NTSC color space. For example, pure white is not allowed. Additionally, colors are automatically "desaturated" to prevent unwanted visual artifacts. The actual adjustments made are slightly different between the three platforms. The TV Producer kit (refer to following "Tools" section) includes a set of Color Tools that can help you pick suitable colors and combinations for the TV screen.

Fonts
The default and minimum font size (HTML font sizes 1-3) for the Liberate compact platform is a rough equivalent of Helvetica 13. Font sizes 4-7 correspond to 14,15,17 and 18 respectively. TV Navigator Standard allows user definition of a minimum font size and sets the default at a rough equivalent of Helvetica 18 . Additionally Liberate allows for customized fonts to be specified on the server, details to follow.

TV Navigator Standard
Generally speaking, iTV applications conform to some aspects of the ATVEF Specification. TV Navigator Standard implementation adheres to the more inclusive SMPTE (Society of Motion Picture and Television Engineers) Content Level 0. The differences are outlined below:

SMPTE Level 0 (TV Navigator Standard)
HTML 3.2
Frames
No CSS
DOM-T (transitional)
JavaScript 1.1

ATVEF
HTML 4.0 (Frameset)
CSS 1
DOM Level 0
ECMAScript
Note: ECMAScript plus DOM Level 0= JavaScript 1.1

However, TV Navigator Standard does support most of the additional HTML functionality described in the ATVEF specification Protocols for TV channel selection, cache control, link navigation, and access to the user interface elements. Finally, The TV Navigator Standard implementation does not currently support the reception and handling of Transport Type B content. The Liberate Mediacast server, however, provides many of the capabilities of Transport Type B. Consult your documentation for details.

TV Navigator Compact V 2.4
The Compact Platform supports an extended subset of HTML 3.2 and HTTP 1.0 similar to the Standard version. The platform supports the standard GIF and PNG MIME types. JPEG, while supported, has proven to be problematic. Additionally, Liberate's Compact Platform provides full support for Frames, AC-3 Audio with the <embed> tag, interactive slideshows, as well as additional protocols for TV channel selection, cache control, link navigation, and access to the user interface elements.

The Compact Platform V2.4 does not support JavaScript extensions to HTML or extensions to HTML forms, though Compact Platform V3.0 supports Java applets. Unsupported features of HTML 3.2 include <basefont>, <dfn>, <link>, <listing>, <samp>, <script>, <strike>, <style>, <sup>, <sub>, and <var> tags. Support of the <embed> and <applet> tags is limited compared to other browsers. Audio formats other than AC-3 are not supported

This information applies specifically to the Compact Platform, but is likely to have a rough analogy in the Standard Platform as well in terms of what material can be accessed. However, regardless of the technical constraints of either platform, access to the outside world is likely to be limited by the MSO whose system you are authoring for, so thought should be given as to what material your users will be able to view.

The Compact Platform views material that has been pre-rendered into a cache on the server. What is loaded into this cache or can be accessed depends on which of three different modes the system is operating in. In Local-Only Mode the browser navigates local content only and does not access the Internet. If a URL is not in the rendered cache, it will not be displayed. Forms cannot be accessed and Server-side image maps are not selectable. In Walled-Garden Mode, a list of valid URLs is specified. Additionally, URLs that are not in the list but have been "crawled" and exist in the page cache can be displayed. In Dynamic Mode all URLs are valid and may be displayed regardless of whether they are cached.

Liberate makes development tools available through their PopTV developers program. The TV Producer kit includes documentation, utilities, examples, the Liberate TV Emulator and a demo version of Macromedia DreamWeaver including templates and added functionality for the Liberate platform. There is an equivalent kit for Compact, TV Producer Compact, which includes similar documentation, examples, and utilities. There is no emulator for the Compact platform at this time.

Liberate Compact Platform
Motorola DCT 2000

Liberate Standard Platform
Pace DiTV 1000, 1000+, 2000, 4000N; Scientific-Atlanta Explorer 2010; Motorola DCT-5000; ST-Micro 20- and 40-based reference platforms; Next Level RG-2000

Liberate Analog Platform
AOLTV, Inprimis

Revised Monday, 10-Mar-2003 14:38:45 CST - h - © 2000 - 2003 Local Enhancement Collaborative & - Please Comment