Why do some mp3s last longer or shorter than their stated track length? In the most extreme case, I have an mp3 here of Feldman's Violin and Orchestra that iTunes says is 7hrs 25mins long (!!! by even Feldman standards). In fact when you play it, it lasts for about an hour.

Lots of my other mp3s - mostly those I've bought from emusic - are slightly longer than they claim to be, seemingly by proportion (so a longer mp3 will be longer than it should be by more than a shorter one, if you see...). Anyone know why this is, and if there's a quick way to correct all these discrepancies. Only a minor annoyance, but still...