FFmpeg Audio Transformer Filter Specification

The FFmpeg Audio Transformer is a wrapper for one or more FFmpeg audio filter effects. The FFmpeg Audio Transformer can be inserted in input and output graphs.

JSON Structure

JS

{
	"name": "FFmpeg Audio Transformer",
    "id": "...",
	"bypass": false/true,
    "configuration": {
        ...
    }
}

Field	Description
id	The FFmpeg Audio Transformer supports updating its settings while the ROAD job is already running. If this feature is to be used, an ID must be specified here to address the filter via ROAD's filterSettings API. The ID is optional; default is empty,
bypass	If `true` , the whole FFmpeg filter chain is bypassed, and the audio passes through the filter unmodified. The setting is optional, default is `false` .
configuration	The list of FFmpeg audio effects, and their settings

JSON Structure of "configuration":

{
  "filters": [
    {
      "filterName": "loudnorm",
      "options": {
        "i": "-24.0",
        "linear": "true"
      }
    },
    {
      "filterName": "aformat",
      "options": {
        "sample_rates": "8000|16000",
        "sample_fmts": "s16"
      }
    }
  ]
}

Field

Description

filters

An array of filter objects (required). A filter object consists of a filterName and options

filterName is the name of the FFmpeg Audio Filter as described on https://ffmpeg.org/ffmpeg-filters.html.
options: A list of key/value pairs, which are passed to the filter. The key/value pairs reflect the ffmpeg.exe command line parameter of the corresponding audio filter. Default: none

Notes:

FFmpeg filter effects, which have non-audio input pads or output pads are not supported.
The version of documentation https://ffmpeg.org/ffmpeg-filters.html may differ from the FFmpeg version used in the DAVID FFmpeg Audio Transformer. This means the documentation may differ from the currently supported version in ROAD.
The mapping between JSON configuration and the command line parameter of FFmpeg.exe can be found in the example below.

How to create the audio filter configuration

Example: Audio Limiter

Go to https://ffmpeg.org/ffmpeg-filters.html
When you search for limiter, you find "alimiter" (https://ffmpeg.org/ffmpeg-filters.html#alimiter)

Optionally, you can use FFmpeg.exe (ffmpeg.exe -hide_banner -h filter=alimiter), which shows you the actual parameters with default and minimum and maximum values

Create the JSON configuration for the ROAD pipe specification

alimiter

JS

{
    "filterName": "alimiter",
    "options": {
        "level_in": 1.0,
        "level_out": 1.0,
        "limit": 1.0,
        "attack": 5.0,
        "release": 50.0,
        "asc": false,
        "asc_level": 0.5,
        "level": true
    }
}

Example: audio compressor

Goto https://ffmpeg.org/ffmpeg-filters.html
When you search for compressor you find acompressor https://ffmpeg.org/ffmpeg-filters.html#acompressor

Optionally, you can use FFmpeg.exe (ffmpeg.exe -hide_banner -h filter=acompressor), which shows you the actual parameters with default and minimum and maximum values

Create the JSON configuration for the Pipe specification

acompressor

JS

{
    "filterName": "acompressor",
    "options": {
        "level_in": 1.0,
        "mode": "downward",
        "threshold": 0.125,
        "ratio": 2.0,
        "attack": 20.0,
        "release": 250.0,
        "makeup": 1.0,
        "knee": 2.82843,
        "link": "average",
        "detection": "rms",
        "level_sc": 1.0,
        "mix": 1.0
    }
}