see: https://twitter.com/inaniwa3/status/941999137226080256

kk.rb

#! ruby -Ku
# coding: utf-8

# usage: ruby kk.rb filename db d
#   ex.) ruby kk.rb hoge.mp4 -30 1.0

require "fileutils"

def argv
  @filename = ARGV[0]
  @db = ARGV[1]
  @d = ARGV[2]
  exit if @d.nil?
  @extname = File.extname(@filename)
  @basename = File.basename(@filename, @extname)
  @workdir = "tmp"
end

def mkdir
  FileUtils.rm_rf(@workdir)
  FileUtils.mkdir_p(@workdir)
end

def detect
  `ffmpeg.exe -i "#{@filename}" -af silencedetect=n=#{@db}dB:d=#{@d} -f null - 2>"#{@workdir}/#{@basename}.txt"`
end

def parse
  lines = open("#{@workdir}/#{@basename}.txt").read.split(/[\r\n]/)
  @ss_t = []
  lines.each do |line|
    if m = line.match(/\[silencedetect @ .+\] silence_start: (.+)/)
      @ss_t << m[1]
    elsif m = line.match(/\[silencedetect @ .+\] silence_end: .+ \| silence_duration: (.+)/)
      @ss_t << m[1]
    end
  end
  @ss_t << nil if @ss_t.length % 2 == 1
end

def cut
  @cutfilenames = []
  (@ss_t.length / 2).times do |i|
    ss = @ss_t[i * 2]
    t = @ss_t[i * 2 + 1]
    @cutfilenames << "#{@basename}.#{i}#{@extname}"
    `ffmpeg.exe -ss #{ss} -i "#{@filename}" #{t.nil? ? "" : "-t #{t}"} "#{@workdir}/#{@cutfilenames.last}" > nul 2>&1`
  end
end

def listname
  s = @cutfilenames.map{|f| "file '#{f}'\n"}.join()
  @listname = "#{@basename}.list"
  File.write("#{@workdir}/#{@listname}", s)
end

def concat
  `ffmpeg -f concat -i "#{@workdir}/#{@listname}" -c copy "#{@basename}.#{@db}.#{@d}#{@extname}" > nul 2>&1`
end

def execute
  argv
  mkdir
  detect
  parse
  cut
  listname
  concat
end

execute