Dolby Atmos

A Dolby Atmos theater includes height channels allowing sounds to be rendered as objects in three dimensional space.

A Dolby Atmos master supports up to 128 audio channels. Each audio channel represents either a direct speaker or to an audio object. The three dimensional position and movement of each object is rendered into the available speaker channels.

Transform supports the following Dolby Atmos master formats:

1. Dolby Atmos Master Format (DAMF). This is the native format produced by the Dolby Atmos mastering tools.
2. Broadcast WAV format (BW64) containing Audio Definition Model (ADM) metadata. This is the format required for iTunes delivery.
3. Material Exchange Format (MXF) containing an Immersive Audio Bitstream (IAB). This is the standard for Atmos delivery within an IMF package.

Transform also support Dolby Atmos channel-based immersive (CBI) audio content in one of the following speaker configurations:

Encoding

Dolby Atmos is encoded using Dolby Digital Plus with Joint Object Coding (JOC). For example the following composition will transcode a Dolby Atmos damf master to a Dolby Digital Plus:

---
input:
  container:
  - name: atmos
    audio:
    - name: a1
output:
  container:
  - name: mp4
    type: 'mp4 '
    audio:
    - route:
        name : a1
      properties:
        AudioNormailzation:
          MeteringMode: bt1770_3
          DialogIntelligence: true
          SpeechThreshold: 25.0
      encode:
        Format: 'atmos'
        properties:
          BitRate: 640000

{
  "input": {
    "container": [
      {
        "name": "atmos",
        "audio": [
          {
            "name": "a1"
          }
        ]
      }
    ]
  },
  "output": {
    "container": [
      {
        "name": "mp4",
        "type": "mp4 ",
        "audio": [
          {
            "route": {
              "name": "a1"
            },
            "properties": {
              "AudioNormailzation": {
                "MeteringMode": "bt1770_3",
                "DialogIntelligence": true,
                "SpeechThreshold": 25.0
              }
            },
            "encode": {
              "Format": "atmos",
              "properties": {
                "BitRate": 640000
              }
            }
          }
        ]
      }
    ]
  }
}

Properties

The Dolby Atmos encoder supports the following properties.

Audio Loudness

The Dolby Atmos encoder requires audio loudness measurements which can be either:

• supplied using the properties described above.
• extracted from Dolby audio metadata present in the master file.
• measured using Audio Normalization.