ARE CODECS STANDALONES OR PART OF THE VIDEO PLAYBACK PROGRAM?
Some players use internal codecs, some players use Windows based standalone codecs, and some players will use internal and standalone codecs. See the “internal codecs” question for more info. With directshow as well as with Video For Windows, codecs are standalones. Both types of codec are simply executable Windows files and the idea for both kinds is that the codec is available to any application that calls for it.