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
www.digitalcabletv.co.uk
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 http://en.wikipedia.org/wiki/MHEG-5 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
http://www.skyinteractive.com/sky/our+servi
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
http://www.planetoftunes.com/dv/stills.html
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
http://developer.msntv.com/tools/colorpick/
Default.htm
Part of the MSN developer network at
http://developer.msntv.com/
Note: we don't use this system in the UK!
Todays task
Re-develop the Bolton.ac.uk homepage for
the NTL system