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FFmpeg loudnorm filter - dual pass loudness normalization example - http://k.ylo.ph/2016/04/04/loudnorm.html
#!/usr/bin/env ruby
require 'open3'
require 'json'
ffmpeg_bin = '/usr/local/bin/ffmpeg'
target_il = -24.0
target_lra = +11.0
target_tp = -2.0
samplerate = '48k'
if ARGF.argv.count != 2
puts "Usage: #{$PROGRAM_NAME} input.wav output.wav"
exit 1
end
ff_string = "#{ffmpeg_bin} -hide_banner "
ff_string += "-i #{ARGF.argv[0]} "
ff_string += '-af loudnorm='
ff_string += "I=#{target_il}:"
ff_string += "LRA=#{target_lra}:"
ff_string += "tp=#{target_tp}:"
ff_string += 'print_format=json '
ff_string += '-f null -'
_stdin, _stdout, stderr, wait_thr = Open3.popen3(ff_string)
if wait_thr.value.success?
stats = JSON.parse(stderr.read.lines[-12, 12].join)
loudnorm_string = '-af loudnorm='
loudnorm_string += 'print_format=summary:'
loudnorm_string += 'linear=true:'
loudnorm_string += "I=#{target_il}:"
loudnorm_string += "LRA=#{target_lra}:"
loudnorm_string += "tp=#{target_tp}:"
loudnorm_string += "measured_I=#{stats['input_i']}:"
loudnorm_string += "measured_LRA=#{stats['input_lra']}:"
loudnorm_string += "measured_tp=#{stats['input_tp']}:"
loudnorm_string += "measured_thresh=#{stats['input_thresh']}:"
loudnorm_string += "offset=#{stats['target_offset']}"
else
puts stderr.read
exit 1
end
ff_string = "#{ffmpeg_bin} -y -hide_banner "
ff_string += "-i #{ARGF.argv[0]} "
ff_string += "#{loudnorm_string} "
ff_string += "-ar #{samplerate} "
ff_string += ARGF.argv[1].to_s
_stdin, _stdout, stderr, wait_thr = Open3.popen3(ff_string)
if wait_thr.value.success?
puts stderr.read.lines[-12, 12].join
exit 0
else
puts stderr.read
exit 1
end
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