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Dolby AC-4 Decoding and Analysis in StreamXpert
Posted on Tuesday, April 2, 2019

AC-4 is Dolby's latest audio compression technology that provides improved bandwidth efficiency, enhanced features and a modern object-based format. Traction in the market is increasing with implementations by several CE manufacturers, inclusion in broadcast standards (ATSC-3, DVB) and many AC-4 broadcast trials being conducted.

StreamXpert decodes AC-4 audio and shows associated metadata in a concise way, both for OTT and transport streams. Broadcasters can use it for confidence monitoring - checking that the audio actually decodes and that all parameters are configured properly. Equipment manufacturers can inspect and verify AC-4 audio and metadata in their product's output.

Dolby AC-4 uses object-based audio to efficiently carry components - music, sound effects and dialogs, possibly in multiple languages - in separate entities on the same PID. Users select a 'presentation', a particular combination of audio components, for listening in their preferred language or for changing between home/away announcers.

Audio objects on the same PID are known as substreams. A presentation is a combination of substreams. The StreamXpert screenshot on the left shows an example of audio substreams and presentations. The dialog is available in English, Spanish and German, while 'music & effects' is in a seperate substream.

When a user changes the presentation, the music & effects substream remains the same but it's combined with a dialog in a different language. This allows AC-4 to send base substreams with a higher bitrate, such as music, only once. With StreamXpert you can examine the details and listen to all presentations.

DekTec has been working closely with Dolby for a long time, so that our tools are instrumented with optimal support for Dolby technologies. Not surprisingly, the decoding- and analysis implementation in StreamXpert is Dolby certified.

Jeff Riedmiller, vice President at Dolby Laboratories comments:

“When launching a next generation audio system like Dolby AC-4, it is critical to have real-time analysis and monitoring tools available not only to ensure compliance with the standard, but to provide the broadcaster with comprehensive visibility into Dolby AC-4’s rich set of metadata – this ensures their next generation audio experiences are optimal when consumed across the wide range of consumer devices and form factors used today. DekTec is a key industry resource helping broadcast services around the world get on air with confidence and we are delighted that StreamXpert now supports Dolby AC-4 with metadata analysis and decoding. This will be a welcome addition to all the broadcasters worldwide who are working to bring Dolby AC-4 enabled experiences to air.”

StreamXpert is DekTec's signature transport-stream analyzer that is standard across the professional broadcast industry. We are constantly updating StreamXpert to keep it current with the latest stream formats. Users with a maintenance arrangement in place have free access to Dolby AC-4 analysis and decoding by upgrading to the latest version.