Karabiner

private.xml

<?xml version="1.0"?>
<root>
  <item>
    <name>Music Controls to Cmd + F13,F14,F15</name>
    <appendix>* Music Prev to Cmd+F13</appendix>
    <appendix>* Music Play/Pause to Cmd+F14</appendix>
    <appendix>* Music Next to Cmd+F15</appendix>
    <identifier>remap.consumer_to_cmd_fkeys_f13</identifier>
    <autogen>__KeyToKey__ KeyCode::F13, ModifierFlag::COMMAND_L, ConsumerKeyCode::MUSIC_PREV</autogen>
    <autogen>__KeyToKey__ KeyCode::F14, ModifierFlag::COMMAND_L, ConsumerKeyCode::MUSIC_PLAY</autogen>
    <autogen>__KeyToKey__ KeyCode::F15, ModifierFlag::COMMAND_L, ConsumerKeyCode::MUSIC_NEXT</autogen>
  </item>
  <item>
    <name>Speaker Controls to F13,F14,F15</name>
    <appendix>* Volume Down to F13</appendix>
    <appendix>* Volume Mute to F14</appendix>
    <appendix>* Volume Up to F15</appendix>
    <identifier>remap.consumer_to_fkeys_f13</identifier>
    <autogen>__KeyToKey__ KeyCode::F13, ConsumerKeyCode::VOLUME_DOWN</autogen>
    <autogen>__KeyToKey__ KeyCode::F14, ConsumerKeyCode::VOLUME_MUTE</autogen>
    <autogen>__KeyToKey__ KeyCode::F15, ConsumerKeyCode::VOLUME_UP</autogen>
  </item>
</root>