missing dvd codec?

does anybody know what codec i might be missing, because whenever i play homemade dvd's on my laptop, i only get video but no audio...and by homemade, i mean stuff that was shot with a camcorder and then burned onto a blank dvd-r, stuff that average joes can do at home...and these dvds do work perfectly normally when i play them on a dvd player on the tv, so it's not as if the dvd is messed up...so does anyone know which codec it might be, or at least know how i can find out which codec i'm missing?