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<font face="Verdana, Arial" size="2">it seems clear to me that if you sign it, you've removed any future commercial use of your music from the mix forever.</font>


The "Attribution-NonCommercial-ShareAlike" license is very broad and I question Magnatune's decision to use it instead of one of the more restrictive Creative Commons licenses.

That said, that specific license doesn't preclude further commerical use of your work. For example, if a film producer wants to use your music in a commerical film, they still have to pay you. But it does remove the commercial incentive to simply reproduce the song and sell it.

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<font face="Verdana, Arial" size="2">I'm not that familar with PRO (ASCAP, BMI, SESAC) agreements, since I haven't deemed it necessary to join one yet, but from what I do know I bet signing an agreement like this, because it is giving away performance rights, would be against the contract you signed with your PRO.</font>


This is actually a VERY valid concern, and I'm taking it straight to Creative Commons to get a response (which I'll post here).