c# and codec audio and video

Hi, I'm new here. I'm not a great C#/.Net programmer. I'd like to program a little application that decode in a memory buffer some all of multimedia file type (like avi, mp3, aac etc...) of all supported format (all installed codec) So 1) I'm a bit confused about codec, which is right name to use? Codec or Dx Filter? 2) I'd like to display all codecs present in a pc 3) There's a place where windows write which codec must used with file extention? 4) I've read about quartz dll but which is the right/fast way to decode in a memory buffer an mp3 or avi? Thanks