I would suggest that you use MPEG Streamclip, which is free. Also get the paid version of Flip4Mac. This enables you to play and convert WMV files on a Mac. It only supplies the codecs you need, so you need MPEG Streamclip to do the actual conversion. (If you have QuickTime Pro version 7, you can do it there as well. Personally, I use MPEG Streamclip because it does the job and is free.)
Once you have both installed, you can convert the file using MPEG Streamclip using Export Audio. Choose AIFF as the format.
many freeware and professional shareware on e-marketing can extract audio from video and trim every para you want, For free you have iTunes.
Go into iTunes preferences and under Advanced tab select Importing tab and change import using WMV encoder to MP3 encoder. Then under then main menus, Advanced, select Convert Selection to MP3. It will leave the original and make an MP3 version.
If you want to pay there is
or just google and try for the best fit you.