No, it wont as there is really no reason that would nessitate re-encoding the audio.... unless you plan to edit it, but even then i dont see a problem.Also, to be honest, if you can get a CD version of your song please do. Don't use a downloaded mp3 unless it is absolutely necessary as your audio quality will suffer through re-encoding. It's just as bad as using divxes as a video source. Buy CDs, ok?
i dont remember whare but i Do remember seeing a recommendation that IF an mp3 was used to start the video edit at the binning of the song.
this is hardly necessary as there is a remarkibly easy work-around.
it is a simple matter to edit how ever much silence you need or want into mp3 iself for intro or epillog. this wont effect the audio qaulity one bit.
in this manner there is no reason to convert the mp3 to wav and back for insertion into the video.

