There is no way you can convert a media playlist file, such as .m3u to actual audio file, which of course includes .m4a (MPEG-4) files as well.
At best, you can open the playlist in some text editor and check for the names of the songs and file paths that are listed in it.
Unfortunately, there is no detailed software record in the database that match this conversion.
M3U
Files with m3u extension can be usually found as playlists, typically for a group of .mp3 files or whole folders.
M4A
Files with m4a extension are audio files stored in MPEG-4 (MP4) container and use AAC (Advanced Audio Coding), or Apple Lossless (ALAC) audio compression. M4A is very popular on Mac computers, because it is default audio format used by iTunes. M4A is also default audio format for Apple portable devices (iPod, iPhone, iPad).