Development on x265 began in March 2013. MulticoreWare made the source code for x265 publicly available On July 23, 2013. The latest stable version (1.4) was released on October 31, 2014.
The x265 project is funded by several companies that direct the development requirements and receive commercial licenses to use x265 in their products without having to release their products under the GPL 2 license. The x265 project has licensed the rights to use the x264 source code for those features that can be used with HEVC. x265 source code is written in C++ and assembly.
x265 supports the Main, Main 10 and Main Still Picture profiles of HEVC, utilizing a bit depth of either 8-bits or 10-bits per sample YCbCr with 4:2:0, 4:2:2 or 4:4:4 chroma subsampling. x265 supports most of the features of x264 including all rate control modes (Constant QP, Constant Rate Factor, Average Bit Rate, 2-pass or multi-pass and Video Buffering Verifier rate control). Visual quality algorithms include CU-Tree (the successor to x264's macroblock-tree), adaptive quantization, b-pyramid, weighted prediction and psycho-visual optimizations (psy-rd and psy-rdoq). A fully lossless mode is also supported.