TV Authoring Guidelines

TV Authoring Guidelines

Enhanced television has aspects of two technologies; computers, where the content is authored, and television, where it is viewed. The television experience has remained essentially the same for fifty years. TV Enhancements must be designed to accommodate the technical limitations and user expectations of the television experience. Every attempt should be made to keep the ITV experience as familiar as possible to the viewer. Keep complexity to a practical minimum and response times short.

Key Differences of Television Viewing (Compared to Web Surfing)
Low resolution: roughly 550x380 viewable pixels (vs. 1024x768 typical)
Distant Viewing: roughly 10-12 feet (vs. 18-24 inches)
Multiple Viewers (vs. single viewer)
Instant Access (vs. waiting for downloaded material)
Simple Remote (vs. mouse)

Avoid Scrolling
People experienced with the world wide web will have little difficulty navigating even the most complex ITV applications. However many viewers have no familiarity with interactive media. For example, when presented with options for scrolling, viewers may become confused and simply ignore them, missing portions of your content entirely.

Keep File Size Small
Many television viewers have never encountered the lengthy downloads common on the World Wide Web, and may assume that you ITV application is broken if it does not load instantly. Although many MSOs bundle hi-speed cable access with their services, great care should be taken to create bandwidth efficient content. Not only are television viewers unaccustomed to lengthy download times, (potentially causing them to ignore content that does not provide instant gratification,) but many ITV platforms such as analog VBI based implementations of ATVEF transport B are by their nature extremely low bandwidth. Solutions can include using more compressed image formats such as GIF and cutting large images into several smaller ones.

Avoid Plug-Ins and Advanced HTML
Even though most ITV systems are based on HTML, it should not be assumed that you will have access to all the resources available in computer based browsers like Netscape and Internet explorer. Implementations of HTML vary significantly from platform to platform and there is only limited support for plug-ins. Unlike a computer, an ITV set-top does not allow the user to install plug-ins.

Keep Pages Simple
The playback platform for ITV applications is a set top box, not a high-speed computer. Hardware intensive activities such as screen redraws are likely to be very slow. Careful consideration must be given to how hard you are taxing the CPU. When ever possible, test content on an actual system before deployment.

Keep Canvas Small
NTSC resolution is variously reported as 720x486 in digital systems to 640x480 in older NLE systems. These numbers describe the absolute limit of the video frame including the edges of the picture which are not visible on a consumer television. The viewable area is referred to as the "video safe area" and is assumed to be the inner 80% of the total screen, giving a 512x384 "safe" area in a 640x480 system.

While 512x384 is the practical maximum size for ITV content, ITV systems use a variety of pixel specifications both larger and smaller than this. Frequently this space is divided between the interactive content and MSO branding and banner ads. An additional complication arises from the fact and many applications automatically re-scale content and font size to fit in the required space, which can cause unexpected results. Finally, these specifications change not only from platform to platform, but MSO to MSO as well. Check the documentation for your platform and your MSO's user interface guidelines for details and when ever possible, test on content on an actual system before deployment.

Keep Text Big
Computer displays are often viewed at a distance of roughly two feet. By contrast, the distance from a viewer to their television is often twelve feet. As a result, fonts in the range of 9 point, while acceptable on a computer, are illegible when viewed on a television. Use 18 point font for standard text and smaller fonts with caution. Be sure to view your design on an actual television. If necessary, buy an NTSC output card for your PC and connect to a TV monitor. You can approximate the effect of TV distance limits by shrinking an image to 320x240 pixels when viewed on a computer monitor.

Computer Display Resolutions vs. Effective TV Resolution (One-Half Scale)
resolution graphic

Work Only in NTSC Safe Colors
While a complete discussion of NTSC color is outside the scope of this document, it must be noted that computer and television video are inherently different. Computer video can display a much wider range of color and luminance. Colors that can be accurately displayed on a television monitor are described as "NTSC color safe" or "video safe" and many applications (such as PhotoShop) provide functions for converting colors to this standard. As a general rule, luminance values of over 80% and RGB component values above 240 should be avoided.

Avoid Narrow Lines
Television systems display video in an interlaced manner, drawing every other horizontal line on each scan. A horizontal line of one pixel in width will be redrawn every other scan causing it to appear to flicker. Accordingly, lines should be a minimum of 2 pixels in width.

Design for Remote Control, Not Mouse
Remember that the most users only have a remote control to navigate and enter data, no mouse or keyboard. Wherever possible, allow viewers to select from choices you present, rather than typing in information. Users with remote controls can only move the cursor up and down and it will stop on every link you define. Accordingly links should be logically laid out for easiest (fewest clicks) navigation.

Don't Assume Internet Access
Regardless of the technical constraints of the platform for which you are authoring, access to the Internet, in fact to any external data, is likely to be limited by the MSO. Thought should be given as to what material you will need or be able to access from the outside world.