Broadcast Trials

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HbbTV

Dolby at the HbbTV Plugfest

By Jacob Smith

This week, I am at the HbbTV Association plugfest in London to test out some of the new audio features that are made possible by the latest HbbTV specification.

The latest HbbTV spec, version 2.0.2, includes support for HDR video and next generation audio, offering a level of experience that was only previously possible via native OTT apps like Netflix and Disney+.

The HbbTV Association holds these plugfests regularly, and they provide a great opportunity for broadcasters, service providers, TV manufacturers and other stakeholders to get together and test that was has been specified on paper actually works – and that new services will work in a predictable way on receivers. They take place in various locations around Europe – this one was hosted in the great facilities of the DTG, the centre for UK digital TV responsible for the D-Book receiver specification.

Our focus this time is on testing some of the AC-4 next generation audio features that are included in HbbTV 2.0.2, and that are now starting to appear in European TVs. In particular, v2.0.2 means that broadcasters can use the AC-4 next generation audio that is shipping in most European UHDTVs not just for broadcast, but for broadband delivery too. That gives a path via broadband for delivering many interesting new features, including immersive 3D sound, enhanced accessibility features and audio personalisation. This path is easy to implement, because it uses existing device capabilities in the field.

For broadband delivered HbbTV services, V2.0.2 enables receivers to identify that they are equipped with AC-4 decoding so that next generation audio content can be targeted at suitably equipped receivers.

We’re seeing a lot of interest from broadcasters in using personalisation aspects of AC-4, where the audio mix can be optimised to suit different viewer preferences or listening scenarios. For example, these can be used to offer a regular audio mix for normal listening and a dialogue-focussed mix for noisy environments, or two different audio mixes of a football game, with different commentators favouring the two teams. HbbTV v2.0.2 provides a means for the HbbTV app to select the audio mix – this is done using the existing HTML5 AudioTrack mechanism in the browser. So a key focus at the plugfest is to try out this new mechanism, and check that it is working on a variety of different browsers and TVs.

It is encouraging to see the progress that the industry is making with implementing these new features. It’ll be great to see services coming to market to take advantage of these new capabilities.

HbbTV with Dolby AC-4

HbbTV can be attractive to broadcasters as a way to innovate services more flexibly, quickly and cost effectively than traditional terrestrial broadcast. This includes the possibility to deliver services that are more immersive and more personalised through use of next generation audio (NGA).

TV models are now coming to market with interesting functionality for making trials and experimental deployments. There are opportunities to collaborate to ensure broadcasters’ needed functionality is implemented in future devices.

At the HbbTV Symposium in November 2019, it was shown how broadcasters can leverage HbbTV and Dolby AC-4 audio to deliver services that are more immersive and more personalised, to mainstream European UHDTVs.

Demonstrations by Dolby and Vewd featured mainstream TV models from Panasonic and Vestel, offering immersive Dolby Atmos sound using the internal speakers of the TV. The rendering in the TVs created a 3D sound image with height, without need for an external soundbar or home cinema system.

One novel aspect was the possibility to add streamed Dolby Atmos immersive audio to existing terrestrial linear broadcast services as a replacement for the normal stereo broadcast audio. As the immersive audio was streamed, it was not necessary to reconfigure the terrestrial multiplex with an extra audio bitstream. The immersive audio was delivered as an AC-4 bitstream via HbbTV, and synchronised with the broadcast video using the HbbTV v2 Media Synchronisation feature. A simple HbbTV app was used which allowed the user to substitute the broadcast stereo audio with the immersive streamed audio by pressing the blue button.

Demonstrations using the Panasonic TV also highlighted the ability to enhance dialogue clarity by boosting the dialogue level within the mix. This was controlled using the Dialogue Enhancement on/off user setting of the TV user interface.

It was also shown that existing TVs can support the overlay of app-generated sounds. This has many potential applications, including the provision of spoken remote control button sounds for the visually impaired (e.g. for ‘play’, ‘pause’, etc). This is achieved while maintaining the full immersive sound experience over speakers and on the HDMI output.

Other trials and demos

Dolby AC-4 over DVB

European national broadcasters
A major French tennis tournament streamed to mobile devices with immersive audio through Dolby AC-4.

RTVE and Cellnex Telecom’s permanent UHD DVB-T2 trial channel uses Dolby AC-4. RTVE broadcast the Change of the Royal Guard live from the Royal Palace in Dolby AC-4 and Dolby Vision.

EBU
European Broadcasting Union groundbreaking high frame rate UHD broadcast trial featured immersive and personalised audio experiences with Dolby AC-4.

Dolby AC-4 over ATSC 3.0

Phoenix Model Market
Phoenix Model Market launched their first
next-generation television channel with Dolby AC-4.

WRAL-TV & NBC UNIVERSAL
WRAL-TV, NBC Universal, and NAB Showcase Next Gen TV
broadcasted Winter Olympic Games with Dolby AC-4.

Dolby AC-4 on NRJ

NRJ conducted broadcast tests for UHD 4K, HDR and Dolby AC-4 over DTTV in Paris and other regions across France (as well as by satellite) on three DTTV channels over two weeks. The first service was in UHD 4K HDR HLG 50p (over 24 Mbps high-speed broadband), the second and third in HD+ 1080p50 HDR HLG at different, lower rates. NRJ combined each of these video flows with a stereophonic audio component coded in Dolby AC-4.

The purpose was to test the video quality over different encoding bitrates as well as the interoperability of video and audio flows with televisions available on the market. After these accomplishments, on the last day of the test, an immersive and multi-language flow was also successfully broadcast on channel 81 in AC-4 and Dolby Vision.

Now we know that as well as the video, many of the 2017 and 2018 TV models sold in France (LG, Samsung, Philips, etc.) are compatible with an AC-4 transmission, in stereo and in immersive or multiple language formats. Many 2019 television models will also support AC-4.

More to come…