x264 is a non paid code library, used to encoding H264/AVC video streams. x264 is written and created by Laurent Aimar, Loren Merritt, Eric Petit(OS X), Min Chen (vfw/asm), Justin Clay(vfw), Måns Rullgård, Christian Heine (asm), and Alex Izvorski (asm).

Features:
* CAVLC/CABAC
* Multi-references
* Intra: all macroblock types (16×16, 8×8, and 4×4 with all predictions)
* Inter P: all partitions (from 16×16 down to 4×4)
* Inter B: partitions from 16×16 down to 8×8 (including skip/direct)
* Ratecontrol: optional VBV, single or multipass ABR, constant quantizer
* Scene cut detection
* Adaptive B-frame placement
* B-frames as references / arbitrary frame order
* 8×8 and 4×4 adaptive spatial transform
* Lossless mode
* Custom quantization matrices
* Parallel encoding of multiple slices

Note: x264 is still in early development stage.