after playing an .m4a, the music player mutes the sound between each song on the playlist

I can play the playlist, but when a .m4a is playing the progress bar is slow and doesn't update very fast, then it mutes between each song and I have to unmute it to hear the music, also If I play about 5 or 6 .m4a songs then the DSM 330 becomes unresponsive except to turn it off, but I will keep playing music, you just can do anything.
Any thoughts. I am using ffdshow for the .m4a, from K-lite codec pack