For most purposes, "raw" audio ("WAV") needs to be compressed. There is a good number of media compression standards, containers and algorithms. I just don't want to overview them all and discuss compatibility; this topic is too big. On most purely audio devices, unfortunately, the dominated format is badly obsolete MP3, followed by proprietary Microsoft WMA. In other media, notably in video, these algorithms have become rare, now better MPEG4 audio is dominating. If your devices use are well-known OS, such as Windows or Android, you have much more freedom. Anyway, of you have properly compressed media file, its further compression is pointless.
Best library and the utility for all kinds of media conversion is FFMpeg or libavcodec:
http://en.wikipedia.org/wiki/FFmpeg[
^],
http://ffmpeg.org/[
^],
http://en.wikipedia.org/wiki/Libavcodec[
^],
http://libav.org/[
^].
It is available on many platforms, including Microsoft's, and on Android:
http://sourceforge.net/projects/ffmpeg4android[
^].
Instead of using the utility by starting a process (which is also a solution), you can use a .NET wrapper. Please see my past answer:
how to convert image to video in C#[
^].
—SA