record via Soundflower with ruby-coreaudio

record_soundflower.rb

#!/usr/bin/env ruby

require "coreaudio"

# Usage: record_soundflower.rb output.m4a

def silent?(wav)
  wav.max == 0 and wav.min == 0
end

# detect Soundflower (2ch) audio device
sf = CoreAudio.devices.find{|dev| dev.name == "Soundflower (2ch)" }

if sf.nil?
  $stderr.puts "cannot found device 'Soundflower (2ch)'"
  exit 1
end

file, = ARGV

if file.nil?
  $stderr.puts "please specify output audio file"
  exit 1
end

begin
  af = CoreAudio::AudioFile.new(file, :write, :format => :m4a)

  buf = sf.input_buffer(4096)
  buf.start

  # skip silence
  loop do
    wav = buf.read(4096)
    unless silent?(wav)
      puts "Start recording."
      af.write(wav)
      break
    end
  end

  max_silence = 44100 * 2 / 4096 # about 2sec
  cnt = 0
  loop do
    wav = buf.read(4096)
    if silent?(wav)
      cnt += 1
      if cnt >= max_silence
        # quit if 2sec of silence continues.
        break
      end
    else
      cnt = 0
    end
    af.write(wav)
  end
  buf.stop
  puts "dropped frames: #{buf.dropped_frame} frames"
ensure
  af.close if af
end