Normalize audio volume using ffmpeg and ruby

audio_volume_normalize.rb

  def normalize_volume(file)
    output = `ffmpeg -i '#{file}' -af "volumedetect" -f null /dev/null 2>&1`
    raise "Error getting audio volume from #{file} (#{$?})" unless $?.success?
    max_volume = output.scan(/max_volume: ([\-\d\.]+) dB/).flatten.first
    mean_volume = output.scan(/mean_volume: ([\-\d\.]+) dB/).flatten.first
    return if !max_volume || !mean_volume
    max_volume = max_volume.to_f
    mean_volume = mean_volume.to_f
    target_volume = -14.0
    adjustment = target_volume - mean_volume
    output_file = "/tmp/#{File.basename(file)}"
    result = system(*['ffmpeg', '-i', file, '-af', "volume=#{adjustment}dB", '-c:v', 'copy', output_file])
    raise "Error normalizing audio volume of #{file}" unless result
    File.rename(output_file, file)
  end