Development on x265 began in March 2013.MulticoreWare made the source code for x265 publicly available On July 23, 2013. The latest stable version (1.7) was released on May 18, 2015.
The x265 project was initially funded by a small group of charter licensee 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, Main12 and Main Still Picture profiles of HEVC (including intra-only profiles), 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. Temporal scalability is supported, allowing for a video to be encoded into a base layer HEVC bitstream that is half the frame rate of the input video frame rate, and an enhancement layer that can be decoded along with the base layer to enable playback at the full frame rate.
In April 2015, at the NAB Show in Las Vegas, MulticoreWare demonstrated high quality real-time 4K 10-bit HEVC encoding at frame rates in excess of 60 FPS on a dual Intel Xeon E5 v3 server, occupying only one standard rack unit.