Perian

Perian is a free, open source QuickTime component that adds native support for many popular video formats. For Mac OS X 10.4.7
Perian enables QuickTime application support for additional Media Types:

• AVI, FLV, and MKV file formats
• MS-MPEG4 v1 & v2, DivX, 3ivX, H.264, FLV1, FSV1, VP6, H263I, VP3, HuffYUV, FFVHuff, MPEG1 & MPEG2 Video, Fraps, Windows Media Audio v1 & v2, Flash ADPCM, Xiph Vorbis (in Matroska), MPEG Layer II Audio
• AVI support for: AAC, AC3 Audio, H.264, MPEG4, and VBR MP3
• Subtitle support for SSA and SRT

Homepage