remix.rb

require 'wav-file'

def cut
  f = open("input.wav")
  format = WavFile::readFormat(f)
  dataChunk = WavFile::readDataChunk(f)
  f.close

  bit = 's*' if format.bitPerSample == 16 # int16_t
  bit = 'c*' if format.bitPerSample == 8 # signed char
  wavs = dataChunk.data.unpack(bit) # read binary

  step = format.hz * format.channel / 20

  loop_total_count = wavs.length / step

  length = wavs.length
  max = 2**(format.bitPerSample-1) * step

  parts = []

  dest = []

  last_is_on = false

  ontime = 0

  while wavs.length > 0 do
    chunk = wavs.slice!(0, step)
    volume = chunk.inject(0){ |a, b| a + b.abs } / max.to_f
    is_on = volume > 0.02

    ontime += step if is_on

    if not last_is_on and is_on

      if ontime < format.hz * format.channel * 0.5
        puts "write volume: #{volume} samples: #{ontime}"
        parts << dest
      end

      dest = []
      ontime = 0
    end
    dest.concat(chunk)
    last_is_on = is_on
  end

  dest.concat chunk

  parts

end

unless File.exists?('dump.txt')
  open('dump.txt', 'w'){ |f|
    f.write Marshal.dump(cut)
  }
end

f = open("input.wav")
format = WavFile::readFormat(f)
dataChunk = WavFile::readDataChunk(f)
f.close
bit = 's*' if format.bitPerSample == 16 # int16_t
bit = 'c*' if format.bitPerSample == 8 # signed char
parts = Marshal.load(open('dump.txt').read)

secs = 60

total_dest = []
index = (parts.length * 0.7).to_i
while total_dest.length < format.hz * format.channel * secs
  total_dest.concat(parts[index])
  index += [1, -1].sample
  index = 0 if index < 0
  index = parts.length-1 if index > parts.length
  p [index, parts[index].length ]
end

dataChunk.data = total_dest.pack(bit)
open("output.wav", "w"){|out|
  WavFile::write(out, format, [dataChunk])
}
dest = []