x265 is an encoder for creating digital video streams in the

High Efficiency Video Coding High Efficiency Video Coding (HEVC), also known as H.265 and MPEG-H Part 2, is a video compression standard designed as part of the MPEG-H project as a successor to the widely used Advanced Video Coding (AVC, H.264, or MPEG-4 Part 10). In compa ...

(HEVC/H.265)

video compression In information theory, data compression, source coding, or bit-rate reduction is the process of encoding information using fewer bits than the original representation. Any particular compression is either lossy or lossless. Lossless compression ...

format developed by the Joint Collaborative Team on Video Coding (JCT-VC). It is available as a command-line app or a

software library In computing, a library is a collection of resources that can be leveraged during software development to implement a computer program. Commonly, a library consists of executable code such as compiled functions and classes, or a library can ...

, under the terms of

GNU General Public License The GNU General Public Licenses (GNU GPL or simply GPL) are a series of widely used free software licenses, or ''copyleft'' licenses, that guarantee end users the freedom to run, study, share, or modify the software. The GPL was the first ...

(GPL) version 2 or later; however, customers may request a commercial license.

History

x265 builds on

source code In computing, source code, or simply code or source, is a plain text computer program written in a programming language. A programmer writes the human readable source code to control the behavior of a computer. Since a computer, at base, only ...

from

x264 x264 is a free and open-source software library and a command-line utility developed by VideoLAN for encoding video streams into the H.264/MPEG-4 AVC video coding format. It is released under the terms of the GNU General Public License. Histo ...

, an open-source video encoder for the previous MPEG video coding standard, H.264/MPEG-4 AVC. The project has licensed the rights to use the x264 source code. Development on x265 began in March 2013. MulticoreWare made the source code for x265 publicly available on July 23, 2013. 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. In February 2014, x265 was integrated into the popular multimedia transcoding tool

FFmpeg FFmpeg is a free and open-source software project consisting of a suite of libraries and programs for handling video, audio, and other multimedia files and streams. At its core is the command-line ffmpeg tool itself, designed for processing vide ...

and its fork Libav. Version 1.0 was completed in May 2014. The stable version (2.0) was released on July 14, 2016.

Technical details

x265 source code is written in C++ and x86 assembly. x265 supports the Main, Main 10, Main 12 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 YCbCr, Y′CbCr, also written as YCBCR or Y′CBCR, is a family of color spaces used as a part of the color image pipeline in digital video and digital photography, photography systems. Like YPbPr, YPBPR, it is based on RGB primaries; the two ...

with 4:2:0, 4:2:2 or 4:4:4

chroma subsampling Chroma subsampling is the practice of encoding images by implementing less resolution for Chrominance, chroma information than for luma (video), luma information, taking advantage of the human visual system's lower acuity for color differences t ...

. x265 supports most of the features of x264 including all rate control modes: Constant QP (CQP), Constant Rate Factor (CRF), Average Bit Rate (ABR), 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 Las Vegas, colloquially referred to as Vegas, is the most populous city in the U.S. state of Nevada and the county seat of Clark County. The Las Vegas Valley metropolitan area is the largest within the greater Mojave Desert, and second-l ...

, 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.

Quality and efficiency

Judged by the objective quality metric VQM in 2015, x265 delivered video quality on par with the reference encoder of the royalty-free VP9 format that competes with HEVC. A codec comparison from 2015 found x265 to be a leading HEVC implementation measured by SSIM metric.Jan Ozer, November 9, 2015
Moscow State Releases First HEVC Comparison
/ref> In August 2016, Netflix published a comparison of x264, VP9, and x265 using video clips from 500 movies and TV shows using 6 different quality metrics and found that both VP9 and x265 have 40%–50% better quality at 1080p than x264. Netflix stated that with the VMAF metric (which closely mirrors human visual experience according to the author) x265 performed substantially (19% to 22%) better than VP9.

Usage

x265 can be invoked as a command-line app or integrated into another application through the

application programming interface An application programming interface (API) is a connection between computers or between computer programs. It is a type of software Interface (computing), interface, offering a service to other pieces of software. A document or standard that des ...

Open-source adopters

Open source software projects which utilize x265 for HEVC encoding: *

Avidemux Avidemux is a free and open-source software application for non-linear video editing and transcoding multimedia files. The developers intend it as "a simple tool for simple video processing tasks" and to allow users "to do elementary things in ...

* HandBrake * Internet Friendly Media Encoder * MeGUI * OpenShot *

ShareX ShareX is a free and open-source screenshot and screencast software for Windows. It is published under the GNU General Public License. The project's source code is hosted on GitHub. It is also available on the Microsoft Store and Steam. Fea ...

* Shotcut * Staxrip * x265vfw

Commercial adopters

Commercial products that utilize x265 for HEVC encoding: * BBright SLED-4K and SLED-HD Encoder * Blackmagic DaVinci Resolve Studio * CloudApp * Sorenson Squeeze Desktop Pro and Squeeze Server * Telestream Vantage Media Processing Platform * TMPGEnc Video Mastering Works * x265 HEVC Upgrade

References

External links

Official website
for the Open Source Project {{Graphics file formats C++ libraries Computer file formats Free software programmed in C++ Free video codecs Free video software Lossy compression algorithms Open standards covered by patents Video compression