Above are different formats and qualities of video files.
High - WMV files for Windows playable with the Windows Media Player for broadband internet connections such as a cable modem or DSL
Low - WMV files for Windows playable with the Windows Media Player for lower speed internet connections such as dial-up
Macintosh / Other - MP4 files for Macintosh or Windows playable with the Real Player or Quicktime for broadband internet connections such as a cable modem or DSL