For 30 years, the DVB Project has been developing technical specifications for digital television. In addition to being commercially driven, interoperability is a fundamental goal of DVB’s work, with the maximum possible commonalities across the different solutions.
While DVB was initially oriented towards Europe, its standards are now used throughout the world, making it a truly global organization. To mark DVB’s 30th anniversary, we invited key contributors to DVB’s work over the years to write about some of the specifications that were most important to DVB’s success.
This feature was first published in Issue 62 of DVB Scene magazine. Read more about the contributors at the end of the page.
Transporting DVB services
Let’s think back 30 years. DVB was in the process of developing its first specification for digital television – later called DVB-S. The members of the DVB consortium had decided that they would accept standards for audio and video coding designed by the Moving Picture Experts Group (MPEG). But what systems layer should be used for the transport of audio, video (and data)?
The Internet Protocol (IP) and the User Datagram Protocol (UDP) existed already but a Real-time Transport Protocol (RTP) was still unknown. It therefore was quite natural to again look at solutions available from MPEG. The MPEG systems layer offered a solution – or two, to be precise: the Packetized Elementary Stream (PES) and the Transport Stream (TS). The beauty of the TS was that it could be made compatible with the requirements of forward error correction (FEC), so important for transmission over error-prone channels.
For the first-generation DVB systems – DVB-S, DVB-C and DVB-T – a concatenation of a convolutional code and a Reed-Solomon code was found to be the optimal and realistic choice with respect to the implementation cost in TV sets of those days. The Reed-Solomon code based on bytes (B) of eight bits each has an implicit limitation: it exists only up to a length of 255 B. In consequence, a data packet including header, payload, and FEC data must not be longer. PES packets are significantly longer. DVB thus selected a TS packet of 188 B and added an FEC block of 16 B. All this was not controversial. What was controversial was the question how many individual TS packets would need to be identifiable. A packet identifier (PID) of 13 bits would support identification of 8,192 packets. By some, this number was considered too small – but it was chosen.
In 2000, I thought that it would be time to replace the TS with a solution available in the IP world. A member of my team in Braunschweig therefore developed a solution described in his dissertation “Transmission of Media Content on IP-based Digital Broadcast Platforms”, which he presented in 2006. To my surprise, the broadcast community had fallen in love with the TS so deeply that our proposal was not taken up. Some 10 years later, ATSC 3.0 arrived as the first all-IP broadcast standard.
Why is the TS a winner? It was chosen for all DVB broadcast solutions including DVB-S2, DVB-T2, DVB-C2, for ATSC 1.0, for ISDBT-T and for DMB-T: a global solution, really.
The DVB codec toolbox
During the infancy of the DVB Project, the MPEG-2 video codec and MPEG-2 Layer II audio codec were the state-of- the-art international standard video and audio codecs from the ISO/IEC and ITU-T-hosted Moving Picture Experts Group. These codecs enabled the compression of video and audio content so that several digital television services could fit into a multiplex that occupied a channel previously occupied by a single analogue television service.
The first edition of DVB BlueBook A001, published in 1996, specified the use of these codecs. With A001 out there, the members of TM-AVC (a subgroup of DVB’s Technical Module) thought they could sit back and wait for the next generation of MPEG technologies to emerge, expected around a decade later. But in 2001, Australia came knocking on DVB’s door with the request to be able to use a, at the time, proprietary audio codec, namely Dolby AC-3, instead of the MPEG offering, within a DVB-based digital television system. After much deliberation, the first and only fully-fledged DVB ‘toolbox’ specification was conceived, at that stage offering two choices of audio codec, where the usual aim was to provide one solution for a given task.
Successive generations of MPEG video codecs have been adopted in order to facilitate successively higher levels of video experience – H.264/AVC in 2006, H.265/HEVC in 2015, and most recently H.266/VVC, along with AVS3, the “next-generation” video codec primarily for use in China. Audio capabilities have been enhanced with multi-channel surround-sound codecs and configurations and MPEG-H 3D Audio. An important element of the toolbox is the set of audio features for accessibility.
Once adopted, audio and video codecs are not usually ever removed from the toolbox. This acknowledges the fact that different regions of the world are at different stages of technology roll-out. With very few exceptions, all of the codecs and their profiles included in BlueBook A001 are in commercial use somewhere in the world. The DVB video and audio coding specification truly embodies the commercially driven, flexible, consensus-based approach to developing industry standards. In my humble opinion, DVB-AVC has helped significantly to underpin the overall success of the DVB Project.
The pay-TV dilemma
One of the key elements in the formation of DVB was the need to bring together differing and sometimes strongly held views about what was needed to create and grow the marketplace. This was particularly the case in the area of the then recently formed pay-TV broadcasters and their juxtaposition with the more traditional public service broadcasters that had been the backbone of broadcasting in Europe since its inception.
The PSBs argued that the market should be ‘open’ and all reception equipment should be harmonized and standardized across the EU (and indeed the world) in the interests of keeping costs to the consumer as low as possible.
The pay-TV broadcasters, on the other hand, needed to incorporate encryption technology into the receiving equipment and insisted on the right to choose their own technology to protect their businesses. Many also felt that the high costs to consumers of reception equipment in the early stages of the market would require direct or indirect subsidy in order to grow the market quickly enough to sustain these high- risk businesses.
Even for the PSBs the need to protect copyright licensing across borders necessitated the use of encryption technology. While the notion of broadcast coverage being limited to the small amount of overspill from terrestrial transmitters might have worked in the pre-satellite world, the pan-European footprint of the new satellites meant that a more robust solution would be needed. This all became known as Conditional Access. It took many often controversial and heated discussions among the market players to establish some areas of commonality on which technical standards could be designed.
Algorithm & interface
The first and most essential of those standards became known as the DVB Common Scrambling Algorithm (CSA). An additional challenge was that while the CSA obviously needed to be secure against hacking, it also needed to be not too secure in order to satisfy the needs of various government intelligence services!
The second area on which it was agreed to develop common standards was around the interfaces to the CSA that would allow proprietary and secret encryption technologies to be deployed by pay-TV broadcasters in such a way that the same common DVB set-top box could be used across the EU to maximize economies of scale in manufacturing. This second set of standards became known as SimulCrypt and MultiCrypt.
It is testament to the visionary work of the DVB pioneers that all three of these standards remain in use today. What allowed that to happen? I think it can be summarized in two words, which together are the cornerstone of much of DVB’s success over the years: compromise and pragmatism.
The satellite success story
Along with the 30th anniversary of the DVB Project itself, in 2023 we also celebrate the 30th anniversary of its first transmission standard, DVB-S. It’s difficult to imagine a world without DVB’s satellite standards. DVB-S, and the standards that followed it, represented a disruptive paradigm shift, first in media distribution and then for a wide variety of other applications, also covering professional and other emerging markets.
DVB-S was designed to provide DTH (direct-to-home) multi-programme television services, pushing several (instead of one) digital television programmes in a single radio frequency channel/transponder. General-purpose multi-transponder (10–20) telecommunications satellites could be used for television broadcasting, rather than the high-power satellites, with four to five transponders, that had been foreseen by the ITU frequency plan agreed in 1977.
DVB-S was an immediate success, thanks to its flexibility to adapt to the multiple needs of the broadcast industry. Widely adopted for satellite broadcast services around the world, it has also been frequently used also for professional transmissions, driving DVB to extend the specifications to cover contribution applications, such as point-to-point connections between television studios and DSNG (digital satellite news gathering) applications.
Contemporarily, DVB-S ‘inspired’ the cable and terrestrial broadcasting systems DVB-C and DVB-T, which, based on independent sub-systems, maintained a high level of commonality with DVB-S, thus reducing implementation effort and time-to-market.
Ten years later, and with clear worldwide success, in 2003 improvements in channel-coding technology that enabled a performance approaching the Shannon limit motivated DVB to define the second-generation standard for satellite transmissions, DVB-S2, once again followed by the terrestrial and cable specifications. The second generation of DVB standards came together with the general migration of broadcast services towards HDTV (and sometimes 4K UHD), to support the incredible evolution of the consumer TV panels (dimension, resolution and dynamics).
DVB-S2 was defined as a single standard to address several satellite applications, from broadcast to broadband and professional ones, thus enabling the use of mass-market products also for professional or other niche applications. And it was another success story, with broad adoption across all the application sectors.
The excellent performance of the second-generation standard made a disruptive third generation unlikely. Nevertheless, another 10 years later, in 2013, DVB started defining DVB-S2X, the extension of DVB-S2 that introduced additional technologies and features to further optimize the core applications of DVB-S2 and complete the application fields of the standard to cover emerging markets such as mobile applications.
DVB’s satellite solutions continue to evolve, most recently adding support for beam-hopping systems and with the initiation of work on adding support for non-geostationary satellite constellations in the second-generation standard for interactive satellite systems, DVB-RCS2. All of this confirms DVB’s position as a leader in satellite specifications.
DVB-SI at your service
The global success of DVB solutions in the marketplace today is based on, and their design inspired by, the MPEG-2 Transport Stream (TS). It is the foundation that shaped everything. But it was not a foundation that came for free. In the first half of the 1990s, the MPEG-2 family of standards were in the process of being conceived to implement pre-recorded media. It was only after players from the broadcast industry approached the MPEG community that, in addition to the Program Stream (PS), which was to be used on DVD media, the TS for use in live broadcast was added to the MPEG-2 specifications.
Apart from its first unique feature at the time (use of two layers of timeline, allowing the terminating device to precisely reconstruct the timing at the source’s input for a smooth presentation), the second big thing about the TS was its layered use of container structures for conveying information about the “core” audiovisual streams in the multiplex. Since DVB calls these services, the container structures conveying information about those services were naturally called service information, or SI for short.
The format of these SI containers (named tables and descriptors) uses the type-length-data design pattern, which makes them extensible yet interoperable, since a receiver can use the length information to skip over the data of a type it does not know about. Instead of defining a container for each use case, DVB partitioned the information into small, (sort of) atomic units, which can be combined to gather all the information needed for a given use case. Effectively, DVB’s tables and descriptors form a domain-specific language for describing the available audiovisual streams and services. From an implementation point of view this enables an implement-once-use- everywhere approach in that, once the implementation of a given container is tested and done, it can be used in many contexts with minimal new testing effort. A first in the media world.
In addition to these microscopic features, it was also the macroscopic, top-level architecture of DVB-SI that gave it a unique advantage.
Television broadcasting happens on many different radio channels, and a receiver can always receive a single channel frequency only. To help ‘agile’ receiver behaviour, DVB-SI can include information about services on other radio channels, too. This allows the receiver to discover available services more quickly, and to alert the user to things of potential interest on radio channels currently not being received. Another first in the media world.
Such architectural patterns would not be picked up by other file and streaming data formats in the media world until much later, and greatly helped the success of DVB technologies in the marketplace.
Ulrich Reimers chaired the DVB Technical Module from the foundation of the DVB Project until 2012. From 1993 to 2020, he was the director of the Institute for Telecommunications Engineering at Technische Universität Braunschweig.
Paul Szucs is vice-chair of the DVB TM-AVC working group. He is Senior Manager, Technology Standards at Sony, a company he has worked with for more than 25 years, focused on standardization, business development and industry alliances.
Vittoria Mignone chairs DVB’s TM-S working group, focused on satellite technologies. Since 1992, she has been with the research centre of Radiotelevisione Italiana, where she is currently head of the Fixed and Mobile Networks Department.
Robin Crossley was involved with the DVB Project from its earliest years and chaired the Conditional Access Specialist group. Now retired, he was previously Director of Technology Development at Sky Group having also worked for SES Astra.
Alexander Adolf is vice-chair of the DVB Technical Module and previously led the working group that developed the DVB-SI specification. He has been involved in the DVB Project and in the development of digital television in Germany for more than 25 years.