Coding & Transport
Video transport covers the packaging and delivery of the video over the underlying network to the receiving device. Technical specifications for the transmission of the base band signals via all sorts of broadcast delivery channels have been among the principal deliverables of the DVB Project.
The DVB specification for native IP broadcasting, DVB-NIP, defines a protocol stack for satellite and terrestrial television broadcasting entirely based on IP and no longer relying on the MPEG-2 Transport Stream layer. DVB-NIP covers, with the same broadcast signal, both professional content distribution applications (to CDN caches, mobile or broadcast tower sites, public hotspots, transportation, etc.) and consumer applications (DTH to IP in-home devices).
DVB-NIP reuses many of the IP standards previously defined by DVB for broadband networks and adapts or complements these for use on DVB broadcast networks. It uses the DVB-I specification for service discovery and programme metadata, the DVB-AVC and DVB-DASH specifications for AV coding and packaging, DVB-MABR for multicast distribution, DVB-GSE (generic stream encapsulation) for link layer adaptation, and finally DVB-S2X and DVB-T2 for physical transport. Additionally, some DVB-HB (Home Broadcast) functionality is used for in-home distribution scenarios.
To support the migration of existing DVB networks, the DVB-NIP standard also includes an optional backwards-compatible mode that uses multi-protocol encapsulation (DVB-MPE) to carry the IP packets within an MPEG-2 Transport Stream, for example using DVB-S2.
Multicast technologies enable a scalable and efficient approach to delivering services over managed networks. DVB’s first specification for Multicast Adaptive Bitrate streaming (DVB-MABR) was published in 2020.
DVB-MABR targets concurrent consumption of the same linear media stream by a large audience, where the number of simultaneous connections to the edge-serving infrastructure carrying the same media payloads would otherwise result in a high degree of duplication.
The advantage of multicast is that it is one-to-many – the content is sent only once for all users, reducing the bandwidth required. It can consequently be prioritized, which guarantees both optimized video resolution and minimal latency.
- Webinar: Multicast ABR opens the door to a new DVB era (March 2020)
- Webinar: Making a case for DVB-MABR (July 2020)
DVB-DASH defines the delivery of live and on-demand TV content over the open internet via HTTP adaptive streaming. It builds on MPEG DASH, which was the first internationally-standardized adaptive bit-rate HTTP-based streaming solution. MPEG DASH is a complex specification with many options, so DVB concentrated on those areas which satisfied the core requirements for live and on-demand use cases. The resulting document is a subset of MPEG DASH with a few extensions along with a set of requirements for the DASH player in the client.
DVB-DASH is normatively referenced in the HbbTV specifications from TS 102 796 v1.4.1 onwards. Many devices in the market support this profile and content providers across Europe have deployed services using the DVB-DASH profile to take advantage of its functionality.
In 2019, DVB added a Low Latency extension to DVB-DASH. This provides consistent delivery of live and linear television over DVB-DASH such that the ‘encoder to screen’ latency as well as start-up delay performance can be on par with other DVB distribution solutions without losing the additional functionalities provided by unicast delivery of television services.
- Webinar: DASH: from on-demand to large scale live for premium services (March 2020)
- Webinar: Encoding and packaging for DVB-I Services (March 2020)
- Webinar: DVB-DASH (June 2018)
- DASH Validator
Audio & Video Coding
TS 101 154 – DVB specification for the use of Video and Audio Coding in Broadcast and Broadband applications – is a core element of all DVB solutions.
TS 101 154 is a “living” document, regularly updated to take account of new market requirements and technology developments. It provides implementation guidelines and conformance points for the use of audio and video coding utilizing MPEG-2 systems in satellite, cable and terrestrial broadcasting systems and in IP-based networks, and for the use of video coding for adaptive bitrate delivery over IP-based networks.
In addition to Standard and High Definition television, the document covers the first and second phase DVB UHDTV specifications (incorporating increased resolution, High Dynamic Range, High Frame Rates and wider colour space) as well as Next Generation Audio systems.
DVB standards are used to deliver satellite television services throughout the world.
The first DVB transmission specification was DVB-S for the satellite delivery of signals. The channel coding tools it described for the first time later became important for all other delivery media as well. DVB-S went on to become the world’s most popular system for the delivery of digital satellite television.
Second Generation Satellite (DVB-S2), developed around 2003, took advantage of advanced techniques for channel coding, modulation and error correction to create a system that made a range of new services commercially viable for the first time. For example, when combined with the latest video compression technology, DVB-S2 enabled the widespread commercial launch of HDTV services.
In 2014, DVB released DVB-S2X, an extension of the DVB-S2 specification that provides additional technologies and features. S2X offers improved performance and features for the core applications of DVB-S2, including Direct to Home (DTH), contribution, VSAT
and DSNG. The specification also provides an extended operational range to cover emerging markets such as mobile applications.
The 2019 revision of DVB-S2X added support for Beam Hopping. In multi-beam satellite systems, this technique enables efficient and flexible use of satellite resources for applications such as VoIP, cellular backhaul, Internet of Things, maritime and in-flight connectivity and government.
DVB-T2 is the world’s most deployed digital terrestrial television (DTT) system owing to its superior robustness, flexibility and efficiency. It supports SD, HD, UHD, mobile TV, radio, and any combination thereof.
DVB-T2 uses OFDM (orthogonal frequency division multiplex) modulation with a large number of sub-carriers delivering a robust signal, and offers a range of different modes, making it a very flexible standard. DVB-T2 uses the same error correction coding as used in DVB-S2, offering a very robust signal. The number of carriers, guard interval sizes and pilot signals can be adjusted, so that the overheads can be optimized for any target transmission channel.
Additional technologies used in DVB-T2 are:
- Multiple Physical Layer Pipes allow separate adjustment of the robustness of each delivered service within a channel to meet the required reception conditions (for example indoor or roof-top antenna). It also allows receivers to save power by decoding only a single service rather than the whole multiplex of services.
- Alamouti coding is a transmitter diversity method that improves coverage in small-scale single-frequency networks.
- Constellation Rotation provides additional robustness for low order constellations.
- Extended interleaving, including bit, cell, time and frequency interleaving.
- Future Extension Frames (FEF) allow the standard to be compatibly enhanced in the future.
DVB-C was first published by ETSI in December 1994, subsequently becoming the most widely used transmission system for digital cable television. The standard is deployed worldwide in systems ranging from the larger cable television networks (CATV) down to smaller satellite master antenna TV (SMATV) systems.
DVB-C became the de facto cable standard worldwide, with the exception of North America, where CableLabs’ DOCSIS (Data over Cable Service Interface Specification) was dominant. ( DVB-C is also integrated as the physical layer for the European version of DOCSIS, ITU J.222.1.) China also remains a major user of DVB-C, using it to deliver TV services to around 160 million households.
While a second generation system, DVB-C2, was developed, it was not deployed in the market. There were several reasons for this, as set out in an article by Peter Siebert in Issue 52 of DVB Scene magazine (on page 14).