DAB over IP

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Abstract

For the transparent consumption of radio services either via Digital Audio Broadcasting (DAB) or Internet Protocol (IP), the same level of metadata and data services for both of the transmissions is necessary. Otherwise, the listener would notice the (even temporary) switch over from DAB+ to IP and back. Rebuilding the same level of audio- and data services compared to DAB, could be difficult in IP delivered scenarios.

This paper presents a technology, to use the DAB Encapsulation of DAB Interfaces (EDI) specification for single service streams as a delivery protocol for IP Radio streaming. The same signal the broadcasters use for the DAB transmission will be reused by a server component which splits the whole ensemble of DAB services into single service EDI streams. Service following becomes easy in the same bitstream, data services and announcements support are included.

The paper includes calculations of the overhead the current technical solution has and gives an outlook on how to reduce this overhead and an overview about the future work.

Introduction

Radio is still an extremely popular medium. Under many different usage scenarios, people can follow a radio program, be provided with news, traffic and weather information, listen to music and simply have fun with it. However, the linear medium of radio faces enormous challenges to the acceptance of listeners. For today’s listeners, access to audio content is as natural as turning on the tap. The success of smart mobile devices, mobile IP connectivity and the fact that most audio content is “device-neutral” means that people can hear almost anything, anywhere, at any time. At the same time, the new audio offerings as podcast and streaming services are multiplying explosively and there is more choice available to listeners than ever before.

Many tongues claim that these developments mean the end of linear radio and that listeners’ needs are met by non-linear, personalised streaming and downloading services. Is that so?

If you put linear live radio and streaming/on-demand audio next to each other and forget the “war of the worlds…” for a moment, a meaningful combination of these two forms holds enormous potential.

For many of its loyal listeners, radio is a medium that is repeatedly switched on because it entertains, informs and frees them from the burden of choosing and becoming active themselves. It offers something new and surprising as well as a kind of an “emotional home” for the listener. OnDemand and streaming, on the other hand, offer control, (almost) limitless choice and direct feedback on the services. The EU-funded project HRADIO wants to show radio stations exactly at the interface of these worlds how such hybrid services look like and how they can be realised on common platforms (Android, iOS and HTML/JS). The following focal points have been identified: Integration of technology, integration of services and integration of the listener.

The development of radio applications is extremely inhomogeneous and diverse. Application developers need a uniform software interface to radio services in order to concentrate on domain-specific tasks and seamlessly integrate radio and on-demand content. At the same time, broadcasters must merge their offerings (broadcast and non-linear) and understand them as a homogeneous service.

To enable developers to concentrate their work fully on the functionality of the applications, the HRADIO project chose the Open Mobile Radio Interface (OMRI) standard as the API to implement access to radio-specific functionalities. OMRI is an API specification currently available as Java API documentation and was standardised by the WorldDAB Technical Committee and ETSI in 2018. As part of HRADIO’s work, the OMRI specification for Android devices with DAB USB receivers was implemented and is used in the project as a basis for the development of hybrid radio mobile applications.

However, it’s clear, that not all of the envisaged end user devices and platforms will be equipped with DAB hardware receivers or are not reasonably usable with a plugged-in receiver device via the USB connector. Therefore, HRADIO applications must be able to utilise pure IP delivery of radio services.

A digital radio service is more than just the stereo audio signal, it is difficult to have a full replacement for DAB signals at the pure IP level. First of all, pure IP streaming services do not have a full replacement to the DAB DynamicLabel or DynamicLabel+ data service. Although there are the so-called ICY tags in Shoutcast1 streams, they cannot reach the functionality of DynamicLabel+ messages and tags. Furthermore, IP Streamed Audio does not offer any alternatives for the slideshow services in DAB, nor does it signal service following and alarm announcements.

These services and signalling surely can be replaced in own application developments by proprietary solutions, but this means a considerable additional development effort as well as additional infrastructure and server capacities. Even if such proprietary solutions exist, they are usually realised over additional IP connections (STOMP, WebSockets, XMLHTTP requests) and do not provide the same level of synchronisation with the audio service as a self-contained system such as DAB.

Therefore, this document proposes the usage of DAB multiplexes in its standardised Encapsulation of DAB Interfaces (EDI) format for the streaming of point to point IP radio services as a replacement for the commonly used Shoutcast streaming.