AWS Elemental Live introduces support for Dolby Atmos® Encoding

In recent years, technology innovation and a drive for an enhanced customer experience have led to broader adoption of Dolby Vision for HDR video and Dolby Atmos for immersive audio.  As the digital media supply chain encompassing content creation, distribution, and consumer consumption matures and expands, customers get the benefit of incredible color, more detailed lowlights, and a high dynamic range with Dolby Vision, as well as an immersive audio experience with Dolby Atmos.

This post focuses on the key benefits of Dolby Atmos, and details how to configure a Dolby Atmos-enabled stream using AWS Elemental Live encoders.

What is Dolby Atmos?

Initially created for the cinema, Dolby Atmos is an innovative audio technology, with sound that moves around you in an immersive experience. While sound recorded in stereo is limited to left and right channels, sound mixed in Dolby Atmos is freed from fixed channels: sound mixers can place individual sounds so they move all around you, and they can also decide the volume, size, and diffusion level of each voice, rustling leaf, or footstep, to reveal nuanced details in the audio.  This unique experience envelops you in sound and places you at the center of the story.

Perspective Detail for 5.1.4 Setup

Dolby Atmos expands on traditional surround sound configurations by adding channels above the listening area, which expands the soundscape and creates an immersive experience. While the Live Dolby Atmos library is capable of other channel configurations (up to 9.1.6), we’ll focus on 5.1.4 since this is the predominant configuration for most Live Atmos events and workflows in use today. 

A common surround sound setup is 5.1 – left, right, and center speakers in front, plus left and right surround speakers; the “.1” is the LFE (Low Frequency Effects) or subwoofer channel. Atmos configurations add height or overhead speakers to the traditional setup, enabling a 5.1.2 or 5.1.4 configuration. These overheads are usually two or four speakers mounted in the ceiling, or via Atmos-enabled speakers that fire sound upward toward the ceiling where it’s reflected down to the listening area. There are also simpler systems utilizing Atmos-enabled soundbars, which provide a similar immersive experience, by up-firing the sound to reflect off the ceiling.

For a complete guide for speaker setup, please refer to the speaker setup guides from Dolby.

Why Dolby Atmos?

Dolby Atmos has been adopted by content creators, broadcasters, and popular streaming services such as Apple TV+, Amazon Prime Video, Netflix, SKY UK, BT Sports, Comcast, and many others. Dolby Atmos is supported in thousands of compatible consumer device models such as phones, tablets, TVs, sound-bars and now even cars. Dolby Atmos is the standard for immersive audio experiences – whether in the cinema, at home, or on the go, consumers can enjoy an experience never heard before.

One advantage of using Dolby Atmos is that it can be enjoyed with most any speaker setup. Instead of carrying pre-mixed audio for a specific speaker setup, Dolby Atmos carries the full experience intended by the artist/live production to any speaker configuration, and the Atmos decoding device then determines how to playback the audio appropriately to the available speakers.

With a software add-on license on your AWS Elemental Live encoder, deploying Dolby Atmos technology is simple and removes the need to purchase additional costly hardware for Dolby Atmos processing.

Scope of support

AWS Elemental Live introduced support for passthrough of Dolby Atmos audio in software release 2.16.3 GA, allowing customers to deliver a Dolby Atmos experience when they have a pre-mixed Dolby Atmos bit stream. Starting with software release 2.22.4 GA, AWS Elemental Live also supports the ability to encode audio sources to Dolby Atmos, and deliver an output in TS, Reliable TS, Apple HLS TS, Apple HLS fMP4, Dash ISO and, TS Archive.

Configuring an event with Dolby Atmos on AWS Elemental Live

Start with the input:

1. Start creating or editing a Live event.
2. In the event, add an input that contains a supported audio source.

A MXF file input source

Now move over to the output side.

3. Find the Apple HLS output tab. You can add multiple outputs in the New Output section.
4. In the Outputs section, for each output stream, select fMP4 as the Segment Type. This setting enables video and audio delivery in fragmented MP4 format. Designate the last stream as audio only.
   

   AWS Elemental Live Outputs configuration

5. In the Streams section, remove the Video configuration for the audio only stream. In the Audio configuration tab, selectDolby Digital Plus with Dolby Atmos in Audio Codec dropdown menu, and select the desired coding mode in the Coding Mode dropdown menu.

Each coding mode has its own associated channel input order. This order must be adhered to closely in order to produce the correct output channels. Here is the default channel order information used in 5.1.4, 7.1.4 and 9.1.6 coding mode.

6. Next, select the proper Bitrate.

Dolby Digital Plus with Dolby Atmos audio codec

Verifying the Output

This information applies if your output is an Apple HLS output group. Elemental Live creates an manifest that complies with the HLS Authoring Specification for Apple Devices.  In the following example, the CODECS attribute in the manifest output includes ‘ec-3’, and the CHANNELS attribute has a value of “12/JOC”, which is the indication that the audio is Dolby Atmos.  The numeric value is the value of the complexity_index_type_a field in the EC3SpecificBox of the Dolby Digital Plus audio track.

#EXTM3U
#EXT-X-VERSION:4
#EXT-X-INDEPENDENT-SEGMENTS
#EXT-X-STREAM-INF:BANDWIDTH=2208800,AVERAGE-BANDWIDTH=2142800,CODECS="avc1.64001f,ec-3",RESOLUTION=1280x720,FRAME-RATE=30.000,AUDIO="program_audio_0"
index_video.m3u8
#EXT-X-MEDIA:TYPE=AUDIO,LANGUAGE="eng",NAME="Alternate Audio",AUTOSELECT=YES,DEFAULT=YES,CHANNELS="12/JOC",GROUP-ID="program_audio_0",URI="index_audio.m3u8"

Summary

Dolby Atmos is an exciting audio technology that delivers an immersive sound experience to your customers. With an add-on software license on your AWS Elemental Live encoder, you can deliver the most compelling, crystal-clear, high-quality video streams accompanied by a vibrant, rich, colorful, and life-like audio experience, without the need to purchase separate, additional hardware for Dolby Atmos processing.

To learn more about AWS Elemental Live visit: https://aws.amazon.com/elemental-live/.

To learn more about Dolby Vision support on AWS Elemental Live, visit: Getting started with AWS Elemental Live and Dolby Vision.