Apple m4a format

I have just discovered that music I downloaded from itunes in m4a format will play on my WD TV Live Plus but music I ripped from my cd collection also in m4a format will NOT play. I noticed that my files ripped from cd are much larger in size. This must be the lossless format with the best quality. For some reason I thought the music downloaded from itunes was also a lossless format. Am I missing something here.

seems to be that is not lossless format as well.