Exporting Slideshow for Web

When I export a 1 minute slideshow for Youtube, Facebook etc the quality is very poor. It is particularly bad when opened full screen. I was able to get an ok quality uploading directly to Youtube but I would expect a much better quality. Can you let me know what settings etc are correct for this type of export.
I am using OS X EI Capitan with FotoMagico 5.0b43 pro version.
Many thanks