Switch between two audio devices on macOS depending on process presence (or other factors).

vban-autoswitch.rb

#!/usr/bin/env ruby

# > vban-autoswitch
# Switches between two audio devices depending on process presence and other conditions.
#
#   @dependency SwitchAudioSource (brew install switchaudio-osx)
#
# Configuration is at the end of this file!
#
# Note: This must be running to work obviously.
# You can use Automator to create an application (run shell script, select ruby as shell and paste the script)
# or create a launchd script to run it at launch.

# ~$ vban-autoswitch
# current audio device: MacBook Pro Speakers
# [2023-12-08 14:52:55] app found (pid=27707)
# [2023-12-08 14:52:55] output audio device set to "BlackHole 2ch"
# [2023-12-08 14:52:55] system audio device set to "BlackHole 2ch"
# [2023-12-08 14:54:55] app quit (was pid=27707)
# [2023-12-08 14:54:55] output audio device set to "MacBook Pro Speakers"
# [2023-12-08 14:54:55] system audio device set to "MacBook Pro Speakers"
# [2023-12-08 14:55:12] app found (pid=27869)
# [2023-12-08 14:55:12] output audio device set to "BlackHole 2ch"
# [2023-12-08 14:55:12] system audio device set to "BlackHole 2ch"
# [2023-12-08 14:55:50] condition failed: ac_power (still running pid=27869)
# [2023-12-08 14:55:50] output audio device set to "MacBook Pro Speakers"
# [2023-12-08 14:55:51] system audio device set to "MacBook Pro Speakers"

# -----------------------

require "shellwords"

class VbanSwitcher
  attr_accessor :debug, :check_start, :check_stop, :switch_system, :process_name, :device_a, :device_b, :notify, :sound_a, :sound_b

  def initialize
    @must_fulfill = {}
    yield(self) if block_given?
  end

  def condition name, interval = false, &block
    @must_fulfill[name] = [block, nil, interval, 0]
  end

  def find_process
    pid = `pgrep -x #{process_name.shellescape}`.chomp
    pid.to_i unless pid.empty?
  end

  def process_alive? pid
    Process.getpgid(pid)
    true
  rescue Errno::ESRCH
    false
  end

  def all_conditions_met?
    @must_fulfill.all? do |name, ref|
      b, v, i, l = ref
      if !i || v.nil? || (Time.now - l).to_i > i
        ref[1] = ref[0].call(self)
        puts "[#{Time.now}] check: #{name} #{ref}" if debug
        ref[3] = Time.now if i
      end
      ref[1]
    end
  end

  def current_device
    `SwitchAudioSource -t output -c`.chomp
  end

  def display_notification key, resolved, sound
    cmd = %{osascript -e 'display notification "► #{resolved.gsub(/'"/, '')}" with title "VBAN-autoswitch" subtitle "switched to #{key}"}
    cmd += %{ sound name "#{sound}"} if sound
    cmd += %{'}
    sleep 1 if sound # or sound may get eaten
    system(cmd)
  end

  def change_device! to
    key = :"DEVICE_#{to}"
    resolved = send(key.to_s.downcase)

    if resolved == current_device
      puts "[#{Time.now}] switching to device `#{key}'(#{resolved}) skipped: already on that device" if debug
    else
      puts "[#{Time.now}] " + `SwitchAudioSource -t output -s #{resolved.shellescape}`.chomp
      puts "[#{Time.now}] " + `SwitchAudioSource -t system -s #{resolved.shellescape}`.chomp if switch_system
      display_notification(key, resolved, send("sound_#{to}".downcase)) if notify
    end
  end

  def wait_for_pid
    if !all_conditions_met?
      unless @has_shown_failed_condition_while_waiting
        puts "[#{Time.now}] condition failed: #{@must_fulfill.map{|n, r| n if r[1] == false }.compact.join(", ")}"
        @has_shown_failed_condition_while_waiting = true
      end
      change_device!(:A) if @first_loop
      sleep check_start
    elsif @pid = find_process
      @has_shown_failed_condition_while_waiting = false
      puts "[#{Time.now}] app found (pid=#{@pid})"
      change_device!(:B)
    else
      puts "[#{Time.now}] app not running" if debug
      change_device!(:A) if @first_loop
      sleep check_start
    end
  end

  def wait_for_quit
    alive = process_alive?(@pid)
    if alive && all_conditions_met?
      puts "[#{Time.now}] app still running (pid=#{@pid})" if debug
      sleep check_stop
    else
      if alive
        puts "[#{Time.now}] condition failed: #{@must_fulfill.map{|n, r| n if r[1] == false }.compact.join(", ")} (still running pid=#{@pid})"
      else
        puts "[#{Time.now}] app quit (was pid=#{@pid})"
      end
      @pid = nil
      change_device!(:A)
    end
  end

  def run!
    puts "current audio device: #{current_device}"
    @first_loop = true

    loop do
      @pid ? wait_for_quit : wait_for_pid
      @first_loop = false
    end
  end
end

VbanSwitcher.new do |app|
  # Device to use when process is ABSENT
  app.device_a = "MacBook Pro Speakers"

  # Device to use when process EXISTS
  app.device_b = "BlackHole 2ch"

  # Process (via pgrep -x) to look for
  app.process_name = "VBAN Talkie Cherry"

  # Also switch system sounds (notifications, etc.)
  app.switch_system = true

  # Message Center notifications
  app.notify = true

  # Sound for switching to either device, "" for default sound, false to disable
  app.sound_a = "Bottle"
  app.sound_b = "Blow"

  # time between checks (in seconds)
  app.check_start = 3.0 # uses pgrep shell-out (slower ~ 0.01 - 0.05)
  app.check_stop  = 1.0 # uses Process.getpgid (very fast < 0.0000)

  # print more information
  app.debug = false

  # Define additional conditions that must be met in order to switch (or stay) on DEVICE_B.
  # Note that these get checked often unless you specify a second argument (seconds to cache the value)
  # Nil's won't get cached so return truthy or literally false.
  #
  #app.condition(:mandatory_unique_name, cache_in_seconds=false) { truthy_value_or_false_but_not_nil }

  # examples deactivated by default, remove this condition (or set it to true) or move/copy the examples
  if false
    # Example: Only on AC-power
    app.condition(:ac_power, 30) do
      power_type = `pmset -g ps|sed -nE "s|.*'(.*) Power.*|\\1|p"`.chomp.downcase.to_sym
      power_type == :ac # or :battery
    end

    # Example: Only when external display(s) are connected
    app.condition(:external_displays, 30) do
      displays = `system_profiler SPDisplaysDataType | grep -c Resolution`.chomp.to_i
      displays > 1
    end

    # Example: Only when specific wifi is connected
    app.condition(:wifi_ssid, 30) do
      # get wifi card (typically en0 or en1, you may hardcode)
      card = `networksetup -listallhardwareports | awk '/Wi-Fi|Airport/{getline; print $2}'`.chomp
      #card = "en0"
      ssid = `networksetup -getairportnetwork #{card.shellescape}`.chomp.split(": ", 2)[1]
      ssid == "MyWifiNetwork"
    end
  end

  app.run!
end