Using iMovie for Audio Slideshows
Instructions:
1) Identify the images you want to use. Put them in a folder “selects.”
2) Open the audio files in Reaper. Edit together a short 2-3 minute clip.
3) In iMovie, go to File > Project Properties and confirm that the image duration is 4 seconds. Make the initial Photo Placement > Crop. Drag your images into iMovie. You can order them by selecting the arrow tool and then dragging and dropping.
4) Drag your audio file on top of your images. If it is too long you can shorten the length but you can’t edit it in iMovie so should go back to Reaper if you want to make edits other than shortening the file. You can add additional files if it is too short. However it is better to edit the two files together in Reaper first.
5) Add text screens by clicking on the T and selecting a type of text screen. Then you drag the text screen to the place where you want it.
6) Using transitions sparingly. It is the button next to the T. Just use cross dissolve and drag it in between the two images you want to transition.
7) You can create a voiceover by clicking on the microphone.
8) When you are done, go to Share > Export using Quicktime
Tutorials
Apple has a series of tutorials.