You should not ever never install any MEGA codec packs!!!
What you need is FFDShow DirectShow Filter. It handles many
video formats, like DivX, XviD, H264 and so on... It also handles many
audio formats, like MP3, AC3*, AAC & Vorbis (OGG).
*Anyway, for AC3 you should install AC3Filter.
Then you need splitters for MKV (Matroska), MP4 & OGG/OGM files. (Windows already got build-in AVI splitter.)
FFDShow:
http://www.afterdawn.com/software/vi...rs/ffdshow.cfm
AC3Filter:
http://ac3filter.net/
MP4 Splitter:
http://www.free-codecs.com/download/MP4_Splitter.htm
Matroska Splitter:
http://www.free-codecs.com/download/...a_Splitter.htm
Ogg DirectShow Filters:
http://www.free-codecs.com/download/...ow_Filters.htm
For MPEG2/DVD playback you need to install MPEG2 decoder, like this one:
http://www.free-codecs.com/download/...der_Filter.htm