http://henrik.nyh.se/2008/09/using-apple-media-keys-over-the-network

back.sh

#!/bin/bash
ssh hyper "osascript -e 'tell app \"iTunes\" to back track'"

mute.sh

#!/bin/bash
ssh hyper "osascript -e 'set volume output muted not (output muted of (get volume settings))'"

name.henriknyh.controlmaster.plist

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>name.henriknyh.controlmaster</string>
    <key>ProgramArguments</key>
    <array>
        <string>/opt/local/bin/ssh</string>
        <string>-MN</string>
        <string>hyper</string>
    </array>
    <key>RunAtLoad</key>
    <true/>
    <key>StandardOutPath</key>
    <string>/dev/null</string>
    <key>StandardErrorPath</key>
    <string>/dev/null</string>
</dict>
</plist>

next.sh

#!/bin/bash
ssh hyper "osascript -e 'tell app \"iTunes\" to next track'"

playpause.sh

#!/bin/bash
ssh hyper "osascript -e 'tell app \"iTunes\" to playpause'"

volume_down.sh

#!/bin/bash
ssh hyper "osascript -e 'set volume output volume (output volume of (get volume settings) - 7)'"

volume_up.sh

#!/bin/bash
ssh hyper "osascript -e 'set volume output volume (output volume of (get volume settings) + 7)'"