Supported File Formats

In addition to file formats that are supported by default (MP3, AVI, WAV, MPG etc) you can install DirectShow filters to add support for new file types

DirectShow Filters

Extension Description Codec/Filter/Driver
MP4 MPEG 4 audio and/or video 3ivx D4 (30 days demo)
M4A MPEG 4 audio only 3ivx D4 (30 days demo)
MOV, QT Apple QuickTime QuickTime Alternative (includes AAC decoder)
OGG, SPX, FLAC, ... Ogg Vorbis, Speex, Theora, FLAC, and WebM Xiph.Org Directshow Filters (Open Source)

Encoders

Extension Description Encoder Software
FLAC Free lossless audio codec FLAC for Windows (Open Source)
OGG Open Source media file OggEnc (Open Source)
SPX Speex: A free codec for free speech Speex Windows binaries (Open Source)

Other Useful Sources

wmplugins.com
Official resources for Microsoft Windows MediaPlayer
ffdshow
Open Source DivX and XviD encoder/decoder
RareWares
Collection of audio codecs for various platforms
vorbis.com
Home of the Open Source Ogg Vorbis format
free-codecs.com
Collecions of misc. codecs
coreaac.corecodec.org
DirectShow filter for AAC
FLAC
Free lossless audio codec
Real Alternative
Play RealMedia files without RealPlayer
BeSweet
Audio transcoding tool that supports MP3,AC3,WAV,MP2,AVI,Aiff,VOB,Ogg Vorbis
WMP Audio Lossless Guide
How to play FLAC, ACE etc. using Windows Media Player and add these files to Media Library