x264 is a free library for encoding H264/AVC video streams. The code is written by Laurent Aimar, Eric Petit(OS X), Min Chen (vfw/nasm), Justin Clay(vfw), Måns Rullgård and Loren Merritt from scratch. It is released under the terms of the GPL license.

WARNING: x264 is still in early development stage

Here are some key features of "x264":

· CAVLC/CABAC
· Multi-references
· Intra: all macroblock types (16x16, 8x8, and 4x4 with all predictions)
· Inter P: all partitions (from 16x16 down to 4x4)
· Inter B: partitions from 16x16 down to 8x8 (including SKIP/DIRECT)
· Ratecontrol: constant quantizer, single or multipass ABR, optional VBV
· Scene cut detection
· Adaptive B-frame placement
· B-frames as references / arbitrary frame order
· 8x8 and 4x4 adaptive spatial transform
· lossless mode

The latest x264 source code can always be found by anonymous SVN repository:

# svn co svn://svn.videolan.org/x264/trunk x264