If you don’t need a wav file, but can work with MPEG audio, here’s what you can do. Get TMPGEnc from
http://www.tmpgenc.net (click on downloads at the top after you select your language). Open TMPGEnc, skip the wizard. Click on File, MPEG Tools. Choose the Simple De-multiplex tool. Browse for your MPEG file and then click run. If you’re using MPEG-1, the audio will be .mp2 and the video will be .m1v. I think MPEG-2 video will be .m2v.