Q: Use only part of a track when adding music to a slideshow

Hello mjfriedman,

Thank you for using Apple Support Communities to post your question. Photos slideshows are an awesome way to show off those great pictures in your collection. To use only part of the track in your project, you would need to use another app to cut, and edit the track first, before adding it to the Slideshow. GarageBand is an excellent app that can be used to edit the part of the track you want to use with your slide show. Please see the links below for more assistance.

GarageBand Help

GarageBand for Mac: Split regions in the Tracks area 

Share songs to iTunes

Photos for OS X: Create and work with slideshows

These links should help you with splitting and using that track in your project. The final result will be awesome!

Have a great day.