DTG Members maintain and support the technical specifications of the DTT platform, known as the D-Book, through numerous expert Working Groups. Whilst ensuring the technical integrity across the D-Book, these DTG Groups also ensure interoperability and define the profiles for the basis of the Freeview and YouView trade mark licenses.

Looking forward, it is vital that DTG Members develop a future roadmap to cover the potential clearance of 700 MHz while resolving the uncertainties, to establish the potential for efficiency improvements from migrating the market to DVB-T2 and to explore the future impact of HEVC.

Current workstreams

  • DTT Platform Steering Group which provides the ongoing technical review of the D-Book, identifies gaps and future work for Working Groups
  • DTG RF Group agreeing the modulation parameters and performance requirements for DTT receivers, including coexistence with other spectrum users such as LTE
  • DTG SI Group defines the profiles of DVB Service Information used on the platform and fills in the gaps where necessary – such as LCNs
  • DTG MHEG Group defines the UK profile of the MHEG-5 standard and acts the rapporteur for the ETSI MHEG Specification.
  • DTG Receiver Recommendations Group agrees the DTT receiver profile requirements.

These DTG Groups are open to Members, contact reception@dtg.org.uk for details.

What is the D-Book?

D-Book coverThe D-Book is the technical specification for UK digital terrestrial television (Freeview and Freeview HD).

The DTG has published and maintained the D-Book for over a decade and the specification is updated annually to keep up with the pace of development in UK DTT.

D-Book 8 was published in March 2015, providing support for the new Freeview Play service, clearance of the 700 MHz band, smart retune to protect user settings during channel changes, over-the-air signalling of software updates via IP, and a standard method for displaying signal strength and quality.

The D-Book is compiled by DTG working groups comprised of the DTG's staff and membership who continually update and peer-review the specification.

The DTG's test centre: DTG Testing tests digital TV products applying for the Freeview, Freeview + and Freeview HD logos against the D-Book standard. Any manufacturer wishing to use the Freeview HD logo on a product must pass the required DTG Testing Freeview HD tests.

The first edition of the D-Book was written in 1996 when the current UK standard for terrestrial broadcasting (DVB-T) was new and untried. Early editions of the D-Book enabled the publication of the European digital TV specification: the E-Book.

In March 2009, the DTG published the 6th edition of the D-Book—enabling the launch of an initial three free-to-air HD channels on Freeview by late 2009, as well as the introduction of a broadband return path which has the potential to be used for streaming on-demand video content such as BBC iPlayer, ITV Player and 4oD, accessing e-government services and allowing viewers to complete transactions via their television. It also introduced DVB-T2, the modulation scheme that is being used in the UK to deliver these services.

In March 2011 the DTG published D-Book 7 which was split into two parts. Part A was the detailed interoperability specification for digital terrestrial television (Freeview HD) while Part B introduced Connected TV and builds on the European HbbTV and OIPF standards to profile enhanced hybrid services. Connected TV is the convergence of ‘traditional’ broadcast digital television and the Internet to deliver new services, applications and programming (both linear and on-demand). D-Book 7 provided an industry-agreed baseline specification for Connected TV products and services that Sky, Virgin Media, YouView and others could build on for trademark requirements to support their services.

D-Book 8 supersedes D-Book 7 Part B, much of which has now been incorporated into HbbTV and is included or referenced in the new edition.

  • D-Book 8 is only available to members of the DTG.

Engineering Channel Over-air Download Schedule

DTG Testing administers The Engineering Channel, carried on Multiplex PSB1 and which is used by manufacturers to download software updates to Freeview/DTT receivers. Over-air downloads scheduled for this week and next are given on the OAD page. A similar system operates for Freesat receivers and the updates currently being broadcast are listed at the bottom of the page. An RSS feed of the schedule is also available.

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.

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.

Overview of MHEG useage in digital TV


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 specification defines the classes and features required to correctly decode and present interactive TV applications, including content formats and APIs that must be implemented for all receivers. It is published as an International ETSI specification, which is further profiled in the D-Book.

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 6.2.1 specification introduced features enabling an MHEG application to utilise the IP connection of the digital television receiver; the MHEG system 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 8 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 UK DTT MHEG profile. DTG Working Groups are open to all Full and New Entrant members.