Multi Platform Apps Week 2 – Interactive TV

Agenda The working Doctor Who example The platforms The players Technical consideration Design Considerations Overall development requirements

Platforms There are several major platforms in use in the UK (the most developed Digital TV country in the world) Sky Digital – 7.6 million subscribers NTL/Telewest Digital – 2.5 million Freeview – 5 million

Projected Digital takeup Courtesy OFCOM

But Each platform has different operating systems and technologies employed NTL/Telewest use the Liberate system which uses HTML Freeview uses MHEG 5 and open standard Sky uses the OpenTV OS but their interactive services can be built in OpenTV or in the new WML for Sky language

NTL/Telewest This system is the closest to web technology Opertaes on a two way interactive broadband link (usually 512K+) Uses HTML and liberate specific extensions Homepage for development hints is that supported by NTL at Includes a downloadable emulator

Freeview system Catching Sky fast Will probably becomes the dominant platform over the course of next 10 years Uses MHEG 5 open standard technology Multimedia and Hypermedia information coding Expert Group See for a definition Works usuing a carousel – play out of data with no return

Sky System Uses Proprietary OpenTV technology and WML based SkyWAP browser (WTVML) for some content Works using a carousel but can also use a 28.8k modem built into the box (mostly for back channel work) More details (and develop tools) at ces/ebusiness/default.htm ces/ebusiness/default.htm ces/ebusiness/default.htm

Design considerations TV's are usually CRT displays They are also worse at displaying content that a CRT computer monitor They are still (and for the forseeable future will probabaly be) the main mechanism for viewing TV in the world They have some real issues as display deveices

Display considerations TV's are non interlaced That means they build the page one line at a time with alternate lines with each pass So pass 1 may get lines 1 then 3 then 5 etc Pass 2 makes up lines 2 then 4 then 6 That is unlike a computer display which builds the full screen each time (interlaced) So PC to TV display is very different

Screen size A PAL screen is.... (come on remember!) But that does not mean you have that to use A safe area is defined in the centre where you can display content This avoids the problems of over scanning or under scanning of the picture This overcomes the problems you will have with the wide range of qualities and age of TV's

Safe and Title Area The Action safe area of a screen is approximately 90% of the screen so on PAL that is –648 x 519 or rounded to 650 x 520 The Title safe area is smaller but again is approximated at 80% of the screen –576 x 461 or rounded to 575 to 460 –Pixel size is different (1.06 width pixel onTV) Good outline at

Buzzing Ever seen someone on tv in a tweed jacket What happens? Because of the low resolution of screen odd numbered thickness lines cause bussing Rememeber don't use single lines in display Also causes problems with text All text and graphics must be anti aliased

Colours Colours bleed into one another Particularly primary colours High contrast between colours causes problems (white and black bleed together) All designs must be tested through a tv first Test colour combinations

Tips A good online tool is available at Default.htm Default.htm Default.htm Part of the MSN developer network at Note: we don't use this system in the UK!

Todays task Re-develop the Bolton.ac.uk homepage for the NTL system