X Codec Pack is virus/spyware/adware/toolbars/search engines free.
All the codecs, filters, tools inside X Codec Pack are freeware.
Inside the package:
XviD : Xvid is an open-source research project focusing on video compression and is a collaborative development effort. All code is released under the terms of the GNU GPL license.
FFDShow: ffdshow tryouts is a DirectShow and Video for Windows codec with support for a wide range of audio and video formats.
AC3 filter: AC3Filter is a high quality free audio decoder and processor filter.
VSFilter: Media Player Classic Home Cinema is a free audio and video player for Windows.
MediaInfo: MediaInfo supplies technical and tag information about a video or audio file.