Wii Transfer supports many movie file types, as well as MP3 and unprotected AAC music files. It even ships with Perian built-in to the application if you don't already have it installed, adding more formats to what QuickTime can support natively. Internally Wii Transfer also uses the open source standard FFMPEG tool, which also is included inside the application bundle and can be replaced with a newer version if you choose.
Some of the common types that Wii Transfer supports:
• MOV
• AVI
• MPEG4
• H.264
• DivX
Learn more: Media Sharing, Converting Movies.