All Screencasts are in ogg video fromat you need to use players like mplayer, kmplayer, kaboodle, kaffine, vlc etc..
Windows Users must have Vlc Player Installed to play these videos or use ffplay
Linux users should not experience any problems while playing these videos cause most Linux distributions natively Supports ogg vorbis
Mac users can use Vlc player too (I dont know wheather or not Mac Supports ogg vorbis natively)