Why will my presentation not load in videos of .avi, .mp4, .mov or .flv formats?

Hi,
I want to load in a number of videos to my prezi but it's not letting me load in videos in .avi, .mov, .flv or .mp4 file formats even though they are supposed to be supported. I don't know much about file formats so I was just wondering whether anyone could shed some light on anything I could be doing wrong when I'm saving these files.
Thanks in advance