UPDATE 2015: The link bewlow doesn’t work anymore but here’s an you can still download MMFix via archive.org. Note that this does not work for 10.9 (readme says it only works for Snow Leopard). There’s an alternative but it doesn’t work for me on Mavericks. (Via)
Here’s a fix by NoMitso to disable the annoying „function“ of OSX to open and play iTunes everytime you use Media Keys on a Mac, rendering them useless for every other audio or video player.
There are articles on Lifehacker and Superuser for this but they have outdated links to NoMitsu’s MMFix.app that fixes this problem, so I thought I’d link to NoMitsus new domain. If this becomes unavailable contact me and I’ll send you the fix. Btw, the readme says it works only on Snow Leopard and was tested with 1.6.2-4, I’m running it on 1.6.8 and it works fine.