LAME Technical FAQ
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There was an observant question during the seminar about why the MP3 file is longer than the original WAV file. The reasons gets at the nittygritty of the MP3 file format, and it's encoder and decoder delays. See questions 1 and 2 in this FAQ of LAME, the MP3 encoder implementation Audacity uses.
Click on LAME Technical FAQ to open the resource.