Multimedia and Hypermedia Experts Group international standards including MHEG-5 for interactive multimedia applications.
MHEG-5 is an international standard for interactive television presentation derived from work in the Multimedia and Hypermedia Experts Group of the International Standards Organisation.
The MHEG-5 UK profile is currently used for the provision of interactive services on digital terrestrial television in the UK where it was first deployed.
Designed for cost-effective implementation on comparatively inexpensive hardware, MHEG-5 capable devices can be produced at very little additional cost to a basic digital receiver.
With a focus on declarative code rather than providing a full procedural programming language, MHEG-5 provides a basic presentation engine specifically intended for interactive applications.
The MHEG programming language includes visible presentation objects, links that respond to events, resident programs and variables. Presentation objects include video, audio, lists, text and graphics. Links trigger events in response to input from the remote control, a timer, a stream event message or the result of a logical condition specified by the programmer. Programs provide basic native functions while variables are used to store integer, boolean, string, object or content references.
A compatible receiver provides an MHEG engine or virtual machine that interprets MHEG applications that are typically broadcast via a carousel file system.
In a broadcast system, an auto-launch application can be associated with a service to execute when a channel is selected. The auto-launch application can then launch other applications or tune to other services. Only one application can run at a time but it is possible to pass information between applications.
Applications can be organised into global application objects and individual scene objects.
In the UK and ETSI profiles, text is presented with a resident Tiresias screen font while graphics objects are presented as line art or PNG bitmaps in a standard 8-bit palette or as MPEG I-Frames.
Information to be presented can either be included as text or graphics embedded in the application, or as referenced content which is acquired from the carousel as required. The latter approach allows the creation of a basic browser application that can be decoupled from dynamically updating data.
The MHP specification has inherited many of the features of the MHEG Profile, including object carousel transmission and the Tiresias system font. Both the MHEG and DVB specification processes are working to ensure that applications from both standards can coexist in a TV service and that MHEG interpreters can be implemented in MHP receivers. This is intended to provide a potential migration path from MHEG to MHP deployment over time as required.
The MHEG-5 standard is available as ISO 13522-5.