You can do it with the most popular Qianqianjingting. First add the video or audio file whose format you want to convert to the playlist, then right-click in the playlist and select Format Conversion. After setting various options, you can convert the format very conveniently. CoolEdit is also okay, but this software is too professional and the operation is complicated. It is not as easy to use as Qianqianjingting

You can download a lot of accompaniments from Decibel.com