What is MHEG?
MHEG (Multimedia Hypertext Experts Group) is standardised open source software that defines the authoring and presentation of interactive applications for digital television. All digital terrestrial television receivers sold in the UK with the Freeview and ‘digital tick’ logo implement MHEG as standard, along with Freesat receivers, to enable them to receive all the broadcast services.
Broadcasters use MHEG to develop applications to enrich the viewing experience; MHEG compliant digital television receivers allow the viewer to access and interact with data services, consumer services, games and interactive advertisements. MHEG applications are also used to provide access to additional video content associated with a broadcast event via an application.
How does it work?
Broadcasters play out the application components via a data carousel injected into the broadcast stream. The MHEG Engine in the compliant digital television receiver decodes and presents the MHEG data stream to the viewer in the form of the interactive application.
Deployments
MHEG is deployed in the UK on both digital terrestrial and digital satellite platforms; variable transmission bandwidth allocated to the MHEG applications makes efficient use of the available broadcast capacity. Applications can make up a dedicated broadcast service or take the form of a small discrete application (a trigger) used to prompt the viewer to a larger MHEG application.
As well as broadcasters controlling the display of an MHEG application, an application can be launched via the television remote control ‘text’ button. Application navigation is defined by key presses on a standard television remote control, including Left, Right, Up, Down and alphanumeric buttons. Use of the remote control colour buttons (Red, Green, Yellow, Blue) is promoted to increase usability.
In addition to interactive applications, MHEG is used in some countries to generate the digital television platform EPG (Electronic Programme Guide)
MHEG-5 Specification
The MHEG-5 Engine specification defines the classes and features required to correctly decode and present interactive TV applications. The MHEG-5 Engine specification includes bitmap object encoding, scaling, tiling and transparency rules and Resident Program descriptions. The MHEG-5 Engine Graphics specification defines the colour palette, colour representation, Line Art and Dynamic Line Art rules, picture and video handling and text control and presentation.
MHEG and Connected TV
Catch-up VoD services traditionally available through an internet connected PC can be written in MHEG to provide the user with access to broadcaster archive content using the digital television receiver and standard remote control. The DTG's D-Book 6.2.1specification defines how the MHEG application utilises the IP connection of the digital television receiver; the MHEG Engine presents a similar user experience to that found on the web, meaning the viewer never misses an episode of their favourite TV programme.
Web-based presentation technologies (HTML, Adobe Flash) can also be optimised in digital television receivers. An MHEG trigger application and IP connection enable the broadcaster to offer the user richer applications and services. Such applications and services have to be developed for remote control user interaction, instead of keyboard and mouse. D-Book 7 defines the rules for the coexistence of different presentation technologies in the Connected TV ecosystem.
DTG MHEG Working Group
The DTG hosts an MHEG working group who manage the evolution of the MHEG 1.06 profile. DTG Working Groups are open to all Principal, Full and New Entrant members.