Ruby CLI Audio Player example using afplay

audio_player.rb

# How to play audio from the command line using afplay. Mac only!

# good reading on working with processes/forks: https://saveriomiroddi.github.io/Executing-and-killing-ruby-parallel-background-jobs/
# afplay: https://ss64.com/osx/afplay.html
# POSIX signals: https://man7.org/linux/man-pages/man7/signal.7.html

# Here's a simple example:
# play a song
process_id = spawn "afplay test.mp3"
# stop playing (make sure to use the same process_id returned by spawn)
Process.kill("SIGKILL", process_id)

# Here's a more advanced version of a class for managing afplay
class AudioPlayer
  def initialize(file_path, options = {})
    @command = file_path + build_options_string(options)
  end
  
  def play
    if @process_id
      # resume playing if the process is already running
      Process.kill("SIGCONT", @process_id)
    else
      # start playing by running 'afplay'
      # fork lets us returns a process_id we can use with other commands
      @process_id = spawn "afplay #{@command}"
    end
  end

  def pause
    # send a stop signal to afplay using the process_id
    Process.kill("SIGSTOP", @process_id)
  end

  def stop
    # send a kill signal to aflpay using the process_id
    Process.kill("SIGKILL", @process_id)
    # detach the process
    detach!
  end

  private

  def build_options_string(options)
    valid_options = %i(volume time rate quality)
    options_string = ""
    options.each do |key, value|
      options_string += " -#{key[0]} #{value}" if valid_options.include?(key)
    end
    options_string
  end

  def detach!
    # detaches process
    Process.detach(@process_id)
    # clear the process_id reference
    @process_id = nil?
  end

  def inspect_process
    # in case this is useful, this will print out the process id and status
    p spawn "ps -O=S -p #{@process_id}"
  end

end

# example usage
player = AudioPlayer.new("test.mp3", volume: 2, time: 10, rate: 0.5)

input = gets.chomp

while input != "exit"
  case input
  when "play"
    player.play
  when "pause"
    player.pause
  when "stop"
    player.stop
  end
  input = gets.chomp
end

# cleanup
player.stop

# if your program doesn't exit cleanly:
# 1. run this command: ps -ax | grep afplay
# 2. look for the process id returned (first column of output), for example: 38062
# 3. kill the process manually: kill -9 38062