slidecast too long

I just published two slidecasts. One of them has an mp3 file of about 6 minutes and the other is about 7 minutes long. The slideshare presentation says that they are 18 minutes and 31 minutes respectively. The mp3 files were uploaded onto slideshare directly; they are not linked from another source. How can I get the length of the slide show to be accurate? (The slide file is in pdf format.)