Audio Operators

The following operators can be applied to an audio stream:

Operator	Type	Description
`volume`	number	Sets the linear gain of an input or output stream.
`mix`	array	Lists the input streams mixed into an output stream.

`volume`

Sets the linear gain of an audio stream. A linear gain of 1.0 represents a logarithmic gain of 0 dB. Linear and logarithmic gains are related as follows:

dB = 20.0 * log10 (volume), volume = pow10 (dB / 20.0)

`mix`

Combines multiple audio streams. Each element of the array supports the following properties:

Property	Type	Description
`name`	string	Identifies the input stream.
`level`	number	Normalized linear gain applied to all input stream channels. A value of 1.0 represents 0 dB gain.
`phase`	number	Rotation applied to all input channels in degrees (0, 90, -90 or 180).
`channel`	array	Lists the input channels mixed into each output channel. The output stream `channels` property determines the dimension of the array. The array items are either the input channel number (1 based) or a channel object as described below.

The channel object identifies a specific input channel. The object supports the following properties:

Property	Type	Description
`channel`	integer	Identifies the input channel by number (1 based).
`label`	enum	Identifies the input channel by speaker label.
`program`	integer	Identifies the input channel by `program` number.
`level`	number	Normalized linear gain applied to the input channel. A value of 1.0 represents 0 dB gain.
`phase`	number	Rotation applied to the input channel in degrees (0, 90, -90 or 180).

The phase property applies a phase rotation (in 90 degree increments) and can be applied to a stream or a specific channel. For example the standard Dolby ProLogic down mix is implemented as follows:

---
input:
  container:
  - name: input1
    audio:
    - name: surround
      channels: 6
      label:
      - L
      - R
      - C
      - LFE
      - Ls
      - Rs
output:
  container:
  - name: output1
    type: 'mp4 '
    audio:
    - name: stereo
      channels: 2
      mix:
      - name: surround
        channel:
        - label: L
        - label: R
      - name: surround
        level: 0.707107
        channel:
        - label: C
        - label: C
      - name: surround
        level: 0.707107
        channel:
        - label: LFE
        - label: LFE
      - name: surround
        phase: -90
        channel:
        - label: Ls
          level: 0.87178
        - label: Ls
          level: 0.489898
      - name: surround
        phase: 90
        channel:
        - label: Rs
          level: 0.489898
        - label: Rs
          level: 0.87178

{
  "input": {
    "container": [
      {
        "name": "input1",
        "audio": [
          {
            "name": "surround",
            "channels": 6,
            "label": [
              "L",
              "R",
              "C",
              "LFE",
              "Ls",
              "Rs"
            ]
          }
        ]
      }
    ]
  },
  "output": {
    "container": [
      {
        "name": "output1",
        "type": "mp4 ",
        "audio": [
          {
            "name": "stereo",
            "channels": 2,
            "mix": [
              {
                "name": "surround",
                "channel": [
                  {
                    "label": "L"
                  },
                  {
                    "label": "R"
                  }
                ]
              },
              {
                "name": "surround",
                "level": 0.707107,
                "channel": [
                  {
                    "label": "C"
                  },
                  {
                    "label": "C"
                  }
                ]
              },
              {
                "name": "surround",
                "level": 0.707107,
                "channel": [
                  {
                    "label": "LFE"
                  },
                  {
                    "label": "LFE"
                  }
                ]
              },
              {
                "name": "surround",
                "phase": -90,
                "channel": [
                  {
                    "label": "Ls",
                    "level": 0.87178
                  },
                  {
                    "label": "Ls",
                    "level": 0.489898
                  }
                ]
              },
              {
                "name": "surround",
                "phase": 90,
                "channel": [
                  {
                    "label": "Rs",
                    "level": 0.489898
                  },
                  {
                    "label": "Rs",
                    "level": 0.87178
                  }
                ]
              }
            ]
          }
        ]
      }
    ]
  }
}