Why won't some of my music play on my iphone?

Most of this music is from cds since none of those are working. Then it's just a few random songs here and there. Is there a quick fix to this? I figured i'd ask here if it was easy enough but if not i'll go to apple support.

Added (1). i forgot to mention that it works perfectly fine on itunes if that makes a difference

CD music moved over to iTunes for use on iPhone must be in MP3 format. Only music format it will play. Check the type of music files those are and if needed convert them to mp3 using a free converter you can download. Best luck.

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