Audio Channel Mapping

Channel Selection

Audio channels are numbered (starting at 1) across all of the audio tracks in a container. For example in a container with two stereo tracks A1 and A2, the channels are numbered 1/2 and 3/4 respectively.

Use the select operator to map specific audio channels to an input stream.

For example the following composition maps the first 8 audio channels from the input1 container to separate surround and stereo input streams:

---
input:
  container:
  - name: input1
    audio:
    - name: surround
      channels: 6
      select:
        channel:
        - 1
        - 2
        - 3
        - 4
        - 5
        - 6
    - name: stereo
      channels: 2
      select:
        channel:
        - 7
        - 8
output:
  container:
  - name: output1
    audio:
    - name: surround
    - name: stereo
{
  "input": {
    "container": [
      {
        "name": "input1",
        "audio": [
          {
            "name": "surround",
            "channels": 6,
            "select": {
              "channel": [
                1,
                2,
                3,
                4,
                5,
                6
              ]
            }
          },
          {
            "name": "stereo",
            "channels": 2,
            "select": {
              "channel": [
                7,
                8
              ]
            }
          }
        ]
      }
    ]
  },
  "output": {
    "container": [
      {
        "name": "output1",
        "audio": [
          {
            "name": "surround"
          },
          {
            "name": "stereo"
          }
        ]
      }
    ]
  }
}

Channel Routing

When a job is submitted the select operator routes channels based on the number of audio tracks found in the input container.

If input1 from the previous example has a single audio track a1 with 8 channels the streams will be routed as shown below:

---
input:
  container:
  - name: input1
    audio:
    - name: a1
      channels: 8
output:
  container:
  - name: output1
    audio:
    - name: surround
      channels: 6
      route:
        name: a1
        channel:
        - 1
        - 2
        - 3
        - 4
        - 5
        - 6
  - name: output2
    audio:
    - name: stereo
      channels: 2
      route:
        name: a1
        channel:
        - 7
        - 8
{
  "input": {
    "container": [
      {
        "name": "input1",
        "audio": [
          {
            "name": "a1",
            "channels": 8 
          }
        ]
      }
    ]
  },
  "output": {
    "container": [
      {
        "name": "output1",
        "audio": [
          {
            "name": "surround",
            "channels": 6,
            "route": {
              "name": "a1",
              "channel": [
                1,
                2,
                3,
                4,
                5,
                6
              ]
            }
          }
        ]
      },
      {
        "name": "output2",
        "audio": [
          {
            "name": "stereo",
            "channels": 2,
            "route": {
              "name": "a1",
              "channel": [
                7,
                8
              ]
            }
          }
        ]
      }
    ]
  }
}

Alternatively, if input1 has 8 discreet audio tracks the streams will be routed as follows:

---
input:
  container:
  - name: input1
    audio:
    - name: a1
    - name: a2
    - name: a3
    - name: a4
    - name: a5
    - name: a6
    - name: a7
    - name: a8
output:
  container:
  - name: output1
    audio:
    - name: surround
      channels: 6
      route:
        channel:
        - name: a1
          channel: 1
        - name: a2
          channel: 1
        - name: a3
          channel: 1
        - name: a4
          channel: 1
        - name: a5
          channel: 1
        - name: a6
          channel: 1
    - name: stereo
      channels: 2
      route:
        channel:
        - name: a7
          channel: 1
        - name: a8
          channel: 1
{
  "input": {
    "container": [
      {
        "name": "input1",
        "audio": [
          {
            "name": "a1"
          },
          {
            "name": "a2"
          },
          {
            "name": "a3"
          },
          {
            "name": "a4"
          },
          {
            "name": "a5"
          },
          {
            "name": "a6"
          },
          {
            "name": "a7"
          },
          {
            "name": "a8"
          }
        ]
      }
    ]
  },
  "output": {
    "container": [
      {
        "name": "output1",
        "audio": [
          {
            "name": "surround",
            "channels": 6,
            "route": {
              "channel": [
                {
                  "name": "a1",
                  "channel": 1
                },
                {
                  "name": "a2",
                  "channel": 1
                },
                {
                  "name": "a3",
                  "channel": 1
                },
                {
                  "name": "a4",
                  "channel": 1
                },
                {
                  "name": "a5",
                  "channel": 1
                },
                {
                  "name": "a6",
                  "channel": 1
                }
              ]
            }
          },
          {
            "name": "stereo",
            "channels": 2,
            "route": {
              "channel": [
                {
                  "name": "a7",
                  "channel": 1
                },
                {
                  "name": "a8",
                  "channel": 1
                }
              ]
            }
          }
        ]
      }
    ]
  }
}

Speaker Selection

The select operator can map audio channels based on speaker labels present in the container:

---
input:
  container:
  - name: input1
    audio:
    - name: surround
      channels: 6
      select:
        channel:
        - label: L
        - label: R
        - label: C
        - label: LFE
        - label: Ls
        - label: Rs
    - name: stereo
      channels: 2
      select:
        channel:
        - label: Lt
        - label: Rt
output:
  container:
  - name: output1
    audio:
    - name: surround
    - name: stereo
{
  "input": {
    "container": [
      {
        "name": "input1",
        "audio": [
          {
            "name": "surround",
            "channels": 6,
            "select": {
              "label": [
                "L",
                "R",
                "C",
                "LFE",
                "Ls",
                "Rs"
              ]
            }
          },
          {
            "name": "stereo",
            "channels": 2,
            "select": {
              "label": [
                "Lt",
                "Rt"
              ]
            }
          }
        ]
      }
    ]
  },
  "output": {
    "container": [
      {
        "name": "output1",
        "audio": [
          {
            "name": "surround"
          },
          {
            "name": "stereo"
          }
        ]
      }
    ]
  }
}

When a job is submitted the operator will route and, if necessary, reorder the channels to match the label selection.

Speaker Assignment

If speaker labels are not present (or incorrect) they can be assigned (or overridden) using the label property:

---
input:
  container:
  - name: input1
    audio:
    - name: surround
      channels: 6
      select:
        channel:
        - 1
        - 2
        - 3
        - 4
        - 5
        - 6
      label:
      - L
      - R
      - C
      - LFE
      - Ls
      - Rs
    - name: stereo
      channels: 2
      select:
        channel:
        - 7
        - 8
      label:
      - L
      - R
output:
  container:
  - name: output1
    audio:
    - name: surround
    - name: stereo
{
  "input": {
    "container": [
      {
        "name": "input1",
        "audio": [
          {
            "name": "surround",
            "channels": 6,
            "select": {
              "channel": [
                1,
                2,
                3,
                4,
                5,
                6
              ]
            },
            "label": [
              "L",
              "R",
              "C",
              "LFE",
              "Ls",
              "Rs"
            ]
          },
          {
            "name": "stereo",
            "channels": 2,
            "select": {
              "channel": [
                7,
                8
              ]
            },
            "label": [
              "L",
              "R"
            ]
          }
        ]
      }
    ]
  },
  "output": {
    "container": [
      {
        "name": "output1",
        "audio": [
          {
            "name": "surround"
          },
          {
            "name": "stereo"
          }
        ]
      }
    ]
  }
}

Program Selection

Channels with identical speaker labels are differentiated by the program number. For example the following composition selects two stereo programs:

---
input:
  container:
  - name: input1
    audio:
    - name: stereo1
      channels: 2
      select:
        channel:
        - label: L
          program: 1
        - label: R
          program: 1
    - name: stereo2
      channels: 2
      select:
        channel:
        - label: L
          program: 2
        - label: R
          program: 2
output:
  container:
  - name: output1
    audio:
    - name: stereo1
    - name: stereo2
{
  "input": {
    "container": [
      {
        "name": "input1",
        "audio": [
          {
            "name": "stereo1",
            "channels": 2,
            "select": {
              "channel": [
                {
                  "label": "L",
                  "program": 1
                },
                {
                  "label": "R",
                  "program": 1
                }
              ]
            }
          },
          {
            "name": "stereo2",
            "channels": 2,
            "select": {
              "channel": [
                {
                  "label": "L",
                  "program": 2
                },
                {
                  "label": "R",
                  "program": 2
                }
              ]
            }
          }
        ]
      }
    ]
  },
  "output": {
    "container": [
      {
        "name": "output1",
        "audio": [
          {
            "name": "stereo1"
          },
          {
            "name": "stereo2"
          }
        ]
      }
    ]
  }
}

Program Assignment

If program numbers are not present they can be assigned using the program property:

---
input:
  container:
  - name: input1
    audio:
    - name: a1
      channels: 4
      label:
      - L
      - R
      - L
      - R
      program:
      - 1
      - 1
      - 2
      - 2
output:
  container:
  - name: output1
    audio:
    - route:
        channel:
        - label: L
          program: 1
        - label: R
          program: 1
    - route:
        channel:
        - label: L
          program: 1
        - label: R
          program: 1
{
  "input": {
    "container": [
      {
        "name": "input1",
        "audio": [
          {
            "name": "a1",
            "channels": 4,
            "label": [
              "L",
              "R",
              "L",
              "R"
            ],
            "program": [
              1,
              1,
              2,
              2
            ]
          }
        ]
      }
    ]
  },
  "output": {
    "container": [
      {
        "name": "output1",
        "audio": [
          {
            "route": {
              "channel": [
                {
                  "label": "L",
                  "program": 1
                },
                {
                  "label": "R",
                  "program": 1
                }
              ]
            }
          },
          {
            "route": {
              "channel": [
                {
                  "label": "L",
                  "program": 1
                },
                {
                  "label": "R",
                  "program": 1
                }
              ]
            }
          }
        ]
      }
    ]
  }
}

Channel Layout

By default each audio stream is mapped to a track in the output container. Use the layout operator to map output channels to specific tracks. Audio channels are numbered (starting at 1) across all the audio tracks in an output container.

For example the following composition uses the select operator to map the first 4 input channels to 2 stereo streams. The input1 container could have either single channel (mono), dual channel (stereo) or multi-channel audio tracks.

The track property defines 4 single channels tracks in the output1 container. The layout operator maps each stereo stream to specific output channels.

---
input:
  container:
  - name: input1
    audio:
    - name: stereo1
      channels: 2
      select:
        channel:
        - 1
        - 2
    - name: stereo2
      channels: 2
      select:
        channel:
        - 3
        - 4
output:
  container:
  - name: output1
    track:
      audio:
      - channels: 1
      - channels: 1
      - channels: 1
      - channels: 1
    audio:
    - name: stereo1
      layout:
        channel:
        - 1
        - 2
    - name: stereo2
      layout:
        channel:
        - 3
        - 4
{
  "input": {
    "container": [
      {
        "name": "input1",
        "audio": [
          {
            "name": "stereo1",
            "channels": 2,
            "select": {
              "channel": [
                1,
                2
              ]
            }
          },
          {
            "name": "stereo2",
            "channels": 2,
            "select": {
              "channel": [
                3,
                4
              ]
            }
          }
        ]
      }
    ]
  },
  "output": {
    "container": [
      {
        "name": "output1",
        "track": {
          "audio": [
            {
              "channels": 1
            },
            {
              "channels": 1
            },
            {
              "channels": 1
            },
            {
              "channels": 1
            }
          ]
        },
        "audio": [
          {
            "name": "stereo1",
            "layout": {
              "channel": [
                1,
                2
              ]
            }
          },
          {
            "name": "stereo2",
            "layout": {
              "channel": [
                3,
                4
              ]
            }
          }
        ]
      }
    ]
  }
}

Optional Channels

Input audio channels may be treated as optional using the select operator.

If an input channel is not present it is replaced with silence in any output stream referencing that channel. If none of the input channels referenced by an output stream are present then the output stream is removed from the composition.

For example the following composition has an optional Spanish language stream on input channels 3/4:

---
input:
  container:
  - name: input1
    audio:
    - name: english
      channels: 2
      select:
        channel:
        - 1
        - 2
    - name: spanish
      optional: true
      channels: 2
      select:
        channel:
        - 3
        - 4
output:
  container:
  - name: output1
    audio:
    - name: english
      language: 'eng'
    - name: spanish
      language: 'spa'
{
  "input": {
    "container": [
      {
        "name": "input1",
        "audio": [
          {
            "name": "english",
            "channels": 2,
            "select": {
              "channel": [
                1,
                2
              ]
            }
          },
          {
            "name": "spanish",
            "optional": true,
            "channels": 2,
            "select": {
              "channel": [
                3,
                4
              ]
            }
          }
        ]
      }
    ]
  },
  "output": {
    "container": [
      {
        "name": "output1",
        "audio": [
          {
            "name": "english",
            "language": "eng"
          },
          {
            "name": "spanish",
            "language": "spa"
          }
        ]
      }
    ]
  }
}

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