Some applications require synchronisation with a television programme running in parallel. Differentiation is generally made between synchronisation points during live programmes (e.g. for sports events) and very precisely timed sequences of synchronisation points (e.g. for Jump&Run games synchronised with the television programme).
Qualitative synchronisation is only possible if the synchronisation points are played back together with the TV signal in multiplex.
In DVB networks it is possible to signal synchronisation points in the form of the DSM-CC stream events defined by MPEG. For precisely timed synchronisation, DVB has specified a virtual timeline (normal play time) which can be applied for synchronisation points.
Applications that are used multiple times are often personalised. It must be possible to permanently store past processes, personal data and user preferences. In most cases a simple model such as website cookies is sufficient. More complex applications may require a complete file system.
Furthermore, saving data locally facilitates an enhancement of the performance due to the temporary storage (caching) of frequently used contents.
Modern iTV concepts often use devices, functions and contents of the home network.
Inputs and outputs
Support is provided to the remote control for the receiver unit as the standard input device. It is necessary to check for duplicate use by the device and the application. Although the use of this is to be viewed as critical, it should be possible to use an infrared keyboard. The future will hopefully bring us support from pointing devices with tactile feedback.
It should be possible to access at least three graphic levels (background, scaled TV picture and application graphic) and the sound system.