x265 is a

software codec A codec is a device or computer program that encodes or decodes a data stream or signal. ''Codec'' is a portmanteau of coder/decoder. In electronic communications, an endec is a device that acts as both an encoder and a decoder on a signal or da ...

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 coding format, 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 ...

(HEVC/H.265) video 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 computer science, a library is a collection of non-volatile resources used by computer programs, often for software development. These may include configuration data, documentation, help data, message templates, pre-written code and sub ...

, under the terms of

GNU General Public License The GNU General Public License (GNU GPL or simply GPL) is a series of widely used free software licenses that guarantee end users the four freedoms to run, study, share, and modify the software. The license was the first copyleft for general ...

(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, is any collection of code, with or without comments, written using a human-readable programming language, usually as plain text. The source code of a program is specially designed to facilitate the w ...

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. Histor ...

, 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 MulticoreWare Inc is a software development company, offering products and services related to HEVC video compression, machine learning (specifically, convolutional neural networks), compilers for heterogeneous computing, and software perform ...

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 of vid ...

and its fork

Libav Libav is an abandoned free software project, forked from FFmpeg in 2011, that contains libraries and programs for handling multimedia data. History Fork from FFmpeg The Libav project was a fork of the FFmpeg project. It was announced on M ...

. 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++ C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significan ...

and

x86 assembly x86 assembly language is the name for the family of assembly languages which provide some level of backward compatibility with CPUs back to the Intel 8008 microprocessor, which was launched in April 1972. It is used to produce object code for ...

. 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, or Y Pb/Cb Pr/Cr, also written as YCBCR or Y′CBCR, is a family of color spaces used as a part of the color image pipeline in video and digital photography systems. Y′ is the luma component and CB and CR are the blue-diff ...

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 chroma information than for luma information, taking advantage of the human visual system's lower acuity for color differences than for luminance. It is u ...

. 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 The Video Buffering Verifier (VBV) is a theoretical MPEG video buffer model, used to ensure that an encoded video stream can be correctly buffered, and played back at the decoder device. By definition, the VBV shall not overflow nor underflow whe ...

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 NAB Show is an annual trade show produced by the National Association of Broadcasters. It takes place in April, and has been held since 1991 at the Las Vegas Convention Center in Las Vegas, Nevada. The show's tagline is "Where Content Comes t ...

Las Vegas Las Vegas (; Spanish for "The Meadows"), often known simply as Vegas, is the 25th-most populous city in the United States, the most populous city in the state of Nevada, and the county seat of Clark County. The city anchors the 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.

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 VP9 is an open and royalty-free video coding format developed by Google. VP9 is the successor to VP8 and competes mainly with MPEG's High Efficiency Video Coding (HEVC/H.265). At first, VP9 was mainly used on Google's video platform YouTube. ...

format that competes with HEVC. A codec comparison from 2015 found x265 to be a leading HEVC implementation measured by

SSIM The structural similarity index measure (SSIM) is a method for predicting the perceived quality of digital television and cinematic pictures, as well as other kinds of digital images and videos. SSIM is used for measuring the similarity between tw ...

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 Video Multimethod Assessment Fusion (VMAF) is an objective full-reference video quality metric developed by Netflix in cooperation with the University of Southern California, The IPI/LS2N lab Nantes Université, and the Laboratory for Image and Vi ...

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.

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 program for Microsoft 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 St ...

* 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 CloudApp is a cross-platform screen capture and screen recording desktop client that supports online storage and sharing. CloudApp full and partial screen recordings export to .mp4 format. Full or partial screen image captures export to either ...

Sorenson Squeeze Sorenson Squeeze was a software video encoding tool used to compress and convert video and audio files on Mac OS X or Windows operating systems. It was sold as a standalone tool and has also long been bundled with Avid Media Composer. History S ...

Desktop Pro and Squeeze Server *

Telestream Telestream, Inc. is an American privately held computer software company. History The company, founded in 1998, is headquartered in Nevada City, California with personnel in France, Germany, Sweden, Poland, Canada and the UK. Telestream prov ...

Vantage Media Processing Platform *

TMPGEnc TMPGEnc or TSUNAMI MPEG Encoder is a video transcoder software application primarily for encoding video files to VCD and SVCD-compliant MPEG video formats and was developed by Hiroyuki Hori and Pegasys Inc.Pegasys IncTMPGEnc User License Agreem ...

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