x264 is an open source and freely distributed command-line software that provides a capable H.264 and MPEG-4 AVC encoder tool for most GNU/Linux operating systems. The project is distributed as part of the VideoLAN project, which develops the powerful VLC Media Player software, and can be used to encode H264/AVC video streams.
Features at a glance
Key features include adaptive B-frame placement, support for custom quantization matrices, support for parallel encoding when running on computers with multiple CPUs, MBAFF (Macroblock-adaptive frame-field) interlacing, conjecture lossless mode, CAVLC and CABAC entropy coding, multi-references, Scene Cut detection, as well as 4x4 and 8x8 adaptive spatial transform.
It uses B-frames as references, supports arbitrary frame order, supports multiple reference frames, uses zone to randomly adjust bitrate distribution, supports all macroblock types, including 4x4, 8x8, 16x16 and PCM with all predictions, supports all Inter P partitions from 16x16 down to 4x4, and all Inter B partitions from 16x16 down to 8x8, including direct and skip.
Supports a wide range of video file formats
The x264 tool supports a wide range of RAW input files, including YUV4MPEG (*.y4m), Avisynth, and all the libav formats. It outputs encoded video files to .264, .mkv, .flv and .mp4 file formats.
Another interesting feature is ratecontrol, which helps to maintain constant quantizer and quality of the encoded video file, as well as single or multipass ABR (Adaptive Bitrate Streaming) and optional VBV (Video Buffering Verifier).
Offers Psy optimizations for detail retention
x264 is also capable of supporting temporal and spatial direct mode in B-frames, as well as adaptive mode selection. Psy optimizations for detail retention are also included in the tool, providing adaptive quantization, psy-trellis and psy-RD.
The program is available for download as part of the VideoLAN project, as a universal tarball archive, which can be installed on any GNU/Linux operating system. It can also be installed from the default software repositories of several distributions.