EBU Publishes Workflow Architecture For Object Audio

The EBU (European Broadcasting Union) has published an architecture outlining workflow for Object Based Audio (OBA) across the whole chain from sound capture to delivery.

The aim of the document is to outline how broadcasters can exploit the benefits of OBA and be ready to incorporate it with the other video elements of Ultra HD over the coming few years. One objective not spelt out directly in the report called Tech Report 042 is to ensure that the workflow meets the particular requirements of video consumption in the modern multiscreen world, which diverge considerably from digital cinema where OBA is also being deployed.

The EBU report is based on work carried out by the Orpheus Project funded by the European Commission, the European Union’s executive body, on object-based audio. This was conducted over about 30 months culminating in May 2018, creating a full toolset for object-based audio covering all stages of the broadcast workflow. The project comprised 10 major European institutions including manufacturers and also research arms of broadcasters such as the BBC, Bayerischer Rundfunk (Bavarian Broadcasting), a public-service radio and television broadcaster, based in Munich, as well as Institut für Rundfunktechnik, the research institute of the public broadcasters of Germany, Austria, and Switzerland.

Also participating was Germany’s Fraunhofer Institute for Integrated Circuits IIS, which specializes in applied media-related research. Fraunhofer was keen to steer the project towards the specific needs of broadcasting by highlighting the distinction between its needs for OBA and those of digital cinema. The point was to avoid the temptation of merely piggy backing on work already carried out for digital cinema, which has been chiefly employing the Dolby Atmos and Barco/Auro 3D systems.

Fraunhofer pointed out that while cinema audiences experience sound in a specialized large room in the reverberant field of loudspeakers, TV viewers hear the audio more directly, even if they are in a home theater.

Furthermore, the home viewer is prepared to take an optimum position for sound and does not expect it to be equally good everywhere in the room, while for a cinema, expectations are equal all over the theatre, even at the edge.

Another distinction is that the size of a cinema means that OBA is expected to deliver spatial accuracy so that people experience sounds coming from the same direction as their source on the screen. The audio follows the object, but that is not required at home so much, even for large screens and not at all for multiscreen devices. Therefore, it would be overkill to invest in expensive capabilities required for large numbers of loudspeakers in a cinema when home viewers can be served by lower cost arrays where aesthetics may be almost as important as sound reproduction.

There are also significant differences relating to OBA in the content itself. In the cinema, viewers normally watch feature films carefully scored and mixed in a post- production environment. While TV users also watch similar films as well as scripted dramas, they consume a diverse range of other content, including news, sports, documentary and reality shows. In many of these cases, audio production does not need to be so sophisticated and in any case the time and resources to post-produce the program in say a remote truck or OB van are not there.

On the other hand, in some respects TV will be more demanding in its requirement to meet the myriad production requirements and consumption patterns of different services, providing features attractive for delivery to mobile devices as well as the big screen. Furthermore, unlike in the cinema, viewers at home or on the road have full use of remote controls, touch screen or tracking devices with ability to change channels, fast-forward through uninteresting content, and adjust the volume while watching. In an OBA world the viewer may want to be able to manipulate the way objects are presented as well.

An underlying requirement for OBA on TV therefore in the multiscreen era is to migrate from a monolithic ‘one-size-fits-all’ approach to both content and presentation, to one that is personalized to a listener’s interests, wishes, and playback environment. So as Fraunhofer pointed out, object-based broadcasting must enable a wide variety of novel interactions with the audio broadcast content, relating both to what is rendered and how that is done. For a particular program and a particular user or audience, a specific subset of the possible interaction features may be selected.

Another key point is that the design of user interfaces can have a profound effect on the total audio experience and so should be considered during creative and editorial processes. This was taken into consideration during Project Orpheus. For example, if a broadcaster wants to provide access to a highly interactive program in a browser, standard web technologies like HTML might be preferable, but if the need is just to add some extra basic graphics or textual information, a stream of inline JSON data within MPEG-DASH would be adequate. JSON (JavaScript Object Notation) is an open-standard file format that uses human-readable text to transmit data objects and is commonly used for asynchronous (not interactive) communication between browsers and servers. Such considerations are summarized in the EBU’s document under the heading of Presentation Design, but broadcasters would need a lot more detail to really grasp some of the issues they will face migrating their audio workflows to OBA. 

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