AFAICR if a patent is not (yet) registered in the US,
>> as far as America is concerned, the patent does not exist.
If this is the case, we need to really move fast to snag the
> patent to hold it open. Aacckk! Neither of you have ever filed a patent, have you?The US and the EU recognize each others patents, insofar as their respective patent laws allow. For example, font designs are not patentable in the US, so the US does not recognize EU patents on font designs. But compression algoritms are patentable in the US, so the US will recognize the EU patent on MP3 compression (assuming it is not trivial, there is no prior art, etc.)
So in theory it is never necessary to file a patent in both places. In practice, people do it sometimes because of: (1) speed -- the other patent office might get done faster -- and (2) legal convenience -- paying a second patent filing fee is cheaper than paying a lawer to argue that the patent would have been accepted had it been filed in the jurisdiction in question.
If you did get an MP3 patent through the USPTO -- and I wouldn't put it past the USPTO to grant it without noticing the EU patent -- then when you came into conflict with Frauenhofer, the EU patent, being earlier, would automatically win.