Slideshow Music

Hi

You can't - you can only add individual songs from your library. And then, only if you own them. If they are from a streaming service (eg apple music) you'll not be able to add them to your slide show.

Which system version do you have installed on your Mac?

In Photos 7 you can built a playlist as a backing track in Photos.

• Select ans open the slideshow project in Photos, then click the Music button with the blue note.
• Remove all entries from the "Selected Music" pane, then click the disclosure button for the Music Library to reveal your Music Library. Now you can click songs in the song list to add them to the backing music. Use the search field to find songs quickly. The song has to be downloaded to your Mac and must not have digital rights assigned, as Tony pointed out. I am using the songs I have arranged with GarageBand and saved to Music.

For example: To open your Music Library in the slideshow:

To add songs to your playlist: You can only select songs that are not greyed out. If they are grey, ensure that they have been downloaded in the Music.app and are stored locally.

Go to the sound settings (you may have a speaker in your menu bar top right if enabled - if not go to system settings, sound and enable the "show volume in menu bar"), and choose your TV as the sound device.