You can only use songs without a digital right protection. Songs you recorded yourself or ripped from unprotected CDs,, songs purchased from the iTunes Store. But Apple Music is protected and cannot be used in a soundtrack for a video, a slideshow, or a memory. If it were possible, you could render the slideshow or memory as a video and remove the protection from the song.
http://help.apple.com/iphone/10/#/iphd4f70e68f
Customize a Memory movie. Tap a Memory movie while it’s playing, then tap the adjust button to do the following:
- Edit the title: Tap Title, tap the title and subtitle to edit them, then choose a title style.
- Choose different music: Tap Music, then choose music from a soundtrack or from your music library (only music you own that’s stored on iPhone is available).
- Choose a custom duration: Tap Duration.
- Choose photos and videos: Tap Photos & Videos, tap , then tap the photos and videos you want in the movie. Deselect photos and videos currently in the Memory movie to remove them.