The GPL is a little complicated, especially when mixing with non-GPL code. There is a FAQ here that may (or may not) help: http://www.gnu.org/licenses/gpl-faq.html
My interpretation of it is that if your code is only loosely tied to getID3 it would be considered a separate program and have no restriction on what license you use. For example, if getID3 sits in its own directory and your code checks to make sure it is there and can still work (or at least not crash, just give a warning like "getID3 files not found, cannot process metadata") if getID3 is missing, then it is a separate program. The user could download a new version of getID3 and upgrade that portion themselves, since it sits by itself.
On the other hand, if you take functions from getID3 source and include it in your own code directly, then it is an integral part of your program and you would need to release your code under the GPL (or compatible license). Or, if you choose not to release your code under the GPL, you would need a getID3 Commercial License (gCL)