Probably the best freeware program available,
SUPER has the ability to convert almost any form of audio/video format to the audio/video format of your choosing.
Before downloading it from the link above, do a Google search for SUPER, from eRight Software. There is plenty of documentation to explain it's capabilities.
I use this program almost every day, it's extremely versatile, and simple to use...and no, I'm not affiliated with them in any way, just a satisfied user of the software.
Randy