Question: iPhoto slideshow export huge file size
I want to export an iPhoto slideshow to a .m4v file. The photos are around 350MB combined. When I try to export as 1080p, I get an error stating that I need more storage space because the resulting file size will be around 64GB. When I export as 720p, the file size will be around 29GB. Even at 720p the movie is 80 times larger than the photos?That can't be accurate.
I found this thread, where the poster had a similar issue and resolved it by rebooting his Mac. No such luck for me.
Any idea what's going on and how I can fix it?
MacBook Pro, macOS High Sierra (10.13.4)