Codec Guide, your source for quality codecs.

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Codecs & DirectShow Filters

LAV Filters (Code - Download - Development builds)
Source filter, audio decoder, and video decoder for many formats.

ffdshow
A DirectShow filter that can decode many audio and video formats.

Haali Media Splitter
Source filter for the Matroska, MP4, Ogg, MPEG and AVI containers.

XviD

madFLAC
Source and decoding filter for FLAC audio.

DC-Bass Source
DC-Bass Source Mod
Source and decoding filter for several audio formats. For example ALAC, AAC, Tracker and TrueAudio.

x264 CLI
x264 VFW

ReClock
Audio renderer with many options. WASAPI output. Audio time stretching (for PAL speedup compensation). Video frame rate correction.

Players

Media Player Classic Home Cinema (MPC-HC)

VideoLAN

ZoomPlayer

Tutorials

Doom9
Lots of encoding tutorials and a forum with multimedia experts.

VideoHelp

Encoding Tools

Handbrake
Excellent video conversion tool.

Avidemux
Excellent video conversion tool.

VirtualDub
Basic video editing and encoding tool.

MeGUI

Muxing Tools

MKVToolnix
A powerful set of tools for (re-)muxing Matroska files.

Burning Tools

ImgBurn

Ripping Tools

DVD Decrypter

Exact Audio Copy

Video Tools

AviSynth

Audio Tools

mpTrim

Miscellaneous Tools

ProgDVB

Bytepointer
Some useful command line file utilities for developers

DVD tools

FixVTS

DVD Rebuilder

DVDSubEdit

IfoEdit

VobBlanker

MenuEdit

Audio

RareWares
Information about AAC, Ogg Vorbis and MPEG4.

Hydrogen Audio
Audio experts

Formats

FourCC.org
List of common Four Character Codes that are used by codecs to identify themselves.

Comparison of container formats