Satsuki Decoder Pack contains video and audio decoders, automatically installable/uninstallable for Windows.The goal of this pack is to decode all types of videos from your PC. This pack doesn't contain codecs, only decoders and filters, that take less place and avoid the conflicts.
The pack in now splitted in 3 files, the main pack, a wm module and a quicktime module. As explained on the decoder pack page, you need the wm module only if you don't have Windows Media Player or more installed.
You also need the QuickTime module only if you don't have quicktime or itunes installed.It make the main decoder pack smaller and will avoid to download the files you don't need (and i can update easyly the pack or any module independently).