K-Lite Codec Pack 2.85 Full
Pre-installation instructions:

It is highly recommended to first uninstall other codec related packages before installing this package. This way your system stays clean and potential problems will be avoided. This installer is able to automatically detect a lot of codec packs and it will ask you if you want to uninstall them.
Close all multimedia applications (media players, video editors, browsers, filesharing tools, etc) before installing this pack.

Installation instructions:

Below on this page you can find some information about all components included in this codec pack. Please read this information thoroughly. Leave all settings in the installer at their default values if you don't know exactly what you should install. Do NOT simply select all components because you think that more means better. In fact, less is better. Many components are not selected by default since it is very unlikely that you actually need them. Click on the 'Print' button to open this documentation in Wordpad. That way you can view it during the entire installation procedure.

Unattended installation:

Run the setup with the command-line parameter -MakeUnattended to create an unattended setup. A wizard called "Unattended Install Maker" will appear. Follow the instructions given in the wizard.

Components:

#   means that ffdshow is able to decode the same format(s) as the marked component. So you don't necessarily need to install the marked component if you install ffdshow.
#   means that Media Player Classic is able to decode the same format(s) as the marked component. So you don't necessarily need to install the marked component if you install MPC and use it as your default player.

Player:

Media Player Classic [version 6.4.9.0+ SVN build 2006-12-24]
This is a full-featured player which has internal decoding support for DVD, MPEG-1/2, MP3, MP2, AAC, AC3 and DTS. It also has internal support for opening MP4, Matroska and Ogg containers. Media Player Classic is also capable of playing QuickTime and RealMedia content if those codecs are installed.

ffdshow:

ffdshow [rev. 971]
ffdshow is a very powerful DirectShow filter can decode various audio and video formats. For example: DivX, Xvid, MPEG-4, H.263, H.264, MPEG1, MPEG2, FLV1, FLV4, MJPEG, CinePack, VP3, huffyuv, Theora, AAC, AC3, DTS, MP1, MP2, MP3 and TrueAudio. When using ffdshow you don't need to install separate DirectShow filters for all of these formats.
ffdshow VFW interface
For encoding into various formats: MPEG-4, DV, H.263, Theora, MPEG-2, MPEG-1, MJPEG and a couple more.
extra plugins
ff_kernelDeint.dll, TomsMoComp_ff.dll, FLT_ffdshow.dll, ff_samplerate.dll

DirectShow video filters:

Xvid [version 1.1.2] #
For decoding Xvid video. This is currently the most popular video format.
DivX [version 6.5.1.0] #
For decoding DivX video.
On2 VP6 [version 6.4.2.0]
For decoding VP6 video. This format is not very common.
On2 VP7 [version 7.0.10.0]
For decoding VP7 video. This format is not very common.
MPEG-1 / MPEG-2 (Cyberlink) [version 6.0.0.3402] # #
MPEG-1 / MPEG-2 (DScaler5) [version 0.0.8.0] # #
MPEG-1 / MPEG-2 (Gabest) [version 1.0.0.3] # #
MPEG-1 / MPEG-2 (MainConcept) [version 1.0.0.78] # #
MPEG-1 / MPEG-2 (Ligos) [version 4.0.0.77] # #
For playing MPEG-1 and MPEG-2 video. Cyberlink and DScaler5 also support playback of DVD video in Windows Media Player and Windows Media Center. A DVD audio decoder needs to be selected separately.

VFW video codecs:

Xvid [version 1.1.2]
For encoding video in the Xvid format.
DivX Pro [version 6.5.0.53]
For encoding video in the DivX format.
x264 [rev. 600]
For encoding video in the H.264 format. We don't recommend using the VFW system to encode H.264 video. It is better to use a CLI based solution, such as MeGUI.
Windows Media 9 VCM [version 9.0.1.1184]
For decoding Windows Media 9 audio and video.
For encoding video in the Windows Media 9 format.
On2 VP6 [version 6.4.2.0] [Encoding]
For encoding video in the VP6 format.
On2 VP7 [version 7.0.10.0] [Encoding]
For encoding video in the VP7 format.
Intel Indeo [version 5.2562.15.54]
For decoding Indeo 5 video.
For encoding video in the Indeo 5 format.
Intel Indeo [version 4.51.16.2]
For decoding Indeo 4 video.
For encoding video in the Indeo 4 format.
Intel Indeo [version 3.24.15.03]
For decoding Indeo 3 video.
For encoding video in the Indeo 3 format.
Intel I.263 [version 2.55.1.16]
For decoding I.263 video.
For encoding video in the I.263 format.
huffyuv [version 2.1.1 CCE Patch 0.2.5]
For decoding huffyuv video.
For encoding video in the huffyuv format.
huffyuv is a lossless (no quality loss) video compression format.
I420 (Helix) [version 1.2]
For decoding from and encoding in the I420 format.
YV12 (Helix) [version 1.2]
For decoding from and encoding in the YV12 format.

DirectShow audio filters:

MP3 (Fraunhofer) [version 1.9.0.311] # #
For decoding MP3 audio.
AC3/DTS/LPCM/MP1/MP2 (AC3Filter) [version 1.11] # #
For decoding AC3 and DTS audio. Also decodes DVD audio.
MP1/MP2 (MainConcept) [version 1.0.0.78] # #
For decoding MP1 and MP2 audio.
Vorbis (CoreVorbis) [version 1.1.0.79] #
For decoding Vorbis audio. This is the recommended Vorbis decoder.
AAC (CoreAAC) [version 1.2.0.575] #
For decoding AAC audio.
MusePack [version 1.0.0.3]
For decoding MusePack audio files (.mpc).
Monkey's Audio [version 1.00]
For decoding Monkey's audio files (.ape).
WavPack (CoreWavPack) [version 1.0.3]
For decoding WavPack audio files (.wv).
FLAC (illiminable) [version 0.73.1936]
For decoding FLAC audio files (.flac).
Voxware MetaSound [version 1.0.0.12]
For decoding Voxware MetaSound audio.

ACM audio codecs:

MP3 (Fraunhofer) [version 3.4.0.0]
MP3 (LAME) [version 3.97]
This can be used to encode MP3 streams/files.
AC3 (ffcHandler) [version 1.3.1]
Required for opening movies that have an AC3 audio stream in applications like VirtualDub.
Vorbis [version 0.0.3.6]
Required for AVI files that contains Vorbis audio. These files are very uncommon.
DivX ;) Audio [version 4.2.0.0]
Some old DivX 3.11 videos use this audio codec.

DirectShow source filters:

AVI splitter (Gabest) [version 1.0.0.7] #
AVI splitter (Haali Media Splitter) [version 1.7.89.0] #
For opening audio and video streams in a AVI container (.avi files).
MP4 splitter (Gabest) [version 1.0.0.3] #
MP4 splitter (Haali Media Splitter) [version 1.7.89.0] #
For opening audio and video streams in a MP4 container (.mp4 files).
Matroska splitter (Haali Media Splitter) [version 1.7.89.0] #
Matroska splitter (Gabest) [version 1.0.2.9] #
For opening audio and video streams in a Matroska container (.mkv and .mka files).
Ogg splitter (Haali Media Splitter) [version 1.7.89.0] #
Ogg splitter (Gabest) [version 1.0.0.0] #
For opening audio and video streams in an Ogg container (.ogm and .ogg files).
FLV splitter (Gabest) [version 1.0.0.1] #
For opening audio and video streams in a FLV container (.flv files).
TS splitter (Haali Media Splitter) [version 1.7.89.0] #
For opening audio and video streams in a MPEG Transport Stream container (.ts and .tp files).
MPEG demuxer (Cyberlink) [version 1.0.0.4528] #
MPEG demuxer (Gabest) [version 1.0.0.3] #
MPEG demuxer (MainConcept) [version 1.0.1.20] #
MPEG demuxer (Elecard) [version 1.0.31.51211] #
MPEG demuxer (Ligos) [version 4.0.0.77] #
For opening audio and video streams in a MPEG Program Stream container (.mpg and .mpeg files).
The Gabest demuxer works best in combination with the Gabest MPEG decoder. The Gabest demuxer also supports .ts files.
The Elecard demuxer should not be used in combination with the DScaler5 MPEG decoder.
The Ligos demuxer only works in combination with the Ligos decoder.
MP3 Source (DCoder) [version 1.3] #
For reading .mp3 files. Works better than the default source filter in Windows.
Ac3/DTS Source (AC3File) [version 0.3a] #
For opening .ac3 and .dts files.
SHOUTcast Source (Gabest) [version 1.0.0.1]
For playing SHOUTcast streams.
AAC parser (Orban) [version 1.0.27]
For playing AAC/HE-AAC/aacPlus streams and .aac files.

DirectShow subtitle filter:

DirectVobSub (a.k.a. VSFilter) [version 2.37 + fixes]
DirectVobSub (a.k.a. VSFilter) [version 2.33]
DirectVobSub is a filter for displaying subtitles (ssa/ass, srt and vobsub). Your subtitle file(s) should have the same filename as your video file (for example: MovieName.avi + MovieName.idx + MovieName.sub) and should be in the same folder as your video file. Then the subtitles will automatically be displayed in most players. Use version 2.33 if you have problems when using version 2.37.

DirectShow audio filters (general purpose):

Morgan Multimedia Stream Switcher [version 0.9.9] #
Morgan Multimedia Stream Switcher can be used to switch between audio streams in an AVI video file that has multiple audio streams. These types of video files are not very common. Both Media Player Classic and BSplayer have this functionality build-in. This means that you do NOT need this filter if you use one of those players.
This filter is known to cause various playback problems, so it is NOT recommended to install this filter.

Audio encoding tools:

LAME CLI and DLL [version 3.97]
Installs LAME CLI (command line interface) and DLL. These can be used by programs like ExactAudioCopy to encode MP3 files.
LameDropXPd [version 3.97]
This tool can be used to encode MP3 files.
OggDropXPd [version 1.8.9 aoTuVb5]
This tool can be used to encode Ogg Vorbis files.

Tools:

GSpot Codec Information Appliance [version 2.70a]
GSpot is a tool that can tell you exactly which codecs are needed to play AVI and MPEG files. It can also perform a render test (for all types video files) that shows you which filters are being used to play that file.
VobSubStrip [version 0.11]
With this tool you can strip languages from VobSub subtitle files (.idx and .sub files).
GraphEdit [build 041201]
GraphEdit is a visual tool for building and testing DirectShow filter graphs.
MMCompView [version 1.10]
This tool shows a list of all installed filters and codecs. It also allows you to enable or disable them.
AVI Fixed [version 2.0b1]
This tool can rebuild the index section of .avi files. This can make files with broken frames playable. In some cases it will also solve synchronisation problems and incorrectly displayed movie lengths.
FourCC Changer
The FourCC (Four Character Code) Changer is a program for changing the FourCC of a video file, which is used to identify which codec should be used to decode the file. This tool is for expert users only.
Bitrate Calculator
This can be used to calculate the bitrate to use when encoding a movie.