How to create duplicate pair of keyboard media keys for use with iTunes and streaming websites
Install Karabiner

Which can be found there: Karabiner: a keyboard customizer for OS X

Analyse which keys are involved

Within Karabiner menu select Launch EventViewer... and type on
the music control key you would like to program.
Here is the output you should get:


Make a private.xml

Read the Karabiner documentation on the topic: private.xml Reference Manual

Create the ${HOME}/Library/Application Support/Karabiner/private.xml
with the following content:

&lt;?xml version="1.0"?&gt;
&lt;root&gt;
  &lt;item&gt;
    &lt;name&gt;Shift standard music control keys&lt;/name&gt;
    &lt;identifier&gt;Shift standard music control keys&lt;/identifier&gt;
    &lt;autogen&gt;__KeyToKey__ ConsumerKeyCode::MUSIC_PREV, ModifierFlag::SHIFT_L, ConsumerKeyCode::MUSIC_PREV&lt;/autogen&gt;
    &lt;autogen&gt;__KeyToKey__ ConsumerKeyCode::MUSIC_PLAY, ModifierFlag::SHIFT_L, ConsumerKeyCode::MUSIC_PLAY&lt;/autogen&gt;
    &lt;autogen&gt;__KeyToKey__ ConsumerKeyCode::MUSIC_NEXT, ModifierFlag::SHIFT_L, ConsumerKeyCode::MUSIC_NEXT&lt;/autogen&gt;
  &lt;/item&gt;
&lt;/root&gt;


Depending of your taste, use vi, emacs or TextEdit
(of course not Word).

If you want to be clean, I would suggest you to proceed as I did.

Create a source with the above content in:

${HOME}/Documents/src/Karabiner/music.xml


and then install it within the Karabiner directory:

cp ${HOME}/Documents/src/Karabiner/music.xml "${HOME}/Library/Application Support/Karabiner/private.xml"


( The "…" use is necessary because of the space within Application Support. ).

Load your private.xml

Tell Karabiner you will use a custom setting:


and load it:


Test it

Check that this let you achieve the mapping you want to get with Chrome.

I didn't check this part of your request, and I am not sure I understood
it fully.

Report success or failure, since this may help some other users .