Now, you can try to compile your codecs from source, and I've certainly done this sort of thing before; I can build my own kernel (In the days BEFORE xconfig), run Slackware/Gentoo, etc. This just didn't work for me.
BUT, there is an easy solution.
Image via CrunchBase
That's right. Upload your video to YouTube, wait for it to process, and download the resulting MP4 from the My Videos area of the control panel. Presto, you've got your audio converted to something usable in short order.