The only option available for Roxio PhotoShow to convert to another video format was the MP4 one. However, Roxio abandoned the application and that service is not available anymore. Basically, a user created a presentation and then used the Share > MP4 option to convert to the specified video format. After a while, he user would receive a link to download the MP4 file. This was the only possibility to export the content to MP4.
I suggest using another application that features various export options including MP4 and any other video formats.