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x265 Encoder

x265 Codec Logo

What is x265?

x265 refers to one of the latest open source video codec used for encoding videos. It is available as free software. The x265 encoder uses the latest x265 codec based on the HEVC High Efficiency Video Coding or H.265 standard. It is licensed under the dual GNU general Public License for commercial and personal use. HEVC is basically a video compression standard that is being developed by ISO/MPEG and Video Coding Experts Group under the name of Joint Collaborative Team on Video Coding or JCT-VC.

The main objective of the JCT-VC is to improve video quality by doubling the data compression ratio of the previous standard known as H.264 encoding standard. The current HEVC compression scale ranges from 320 by 240 pixels to 7680 x 4320 pixels. HEVC is usually referred to as H.265 because it is the successor of the former H.264. It is also known as MPEG-H in some circles but its standard name is HEVC. The recent history of x265 can be traced back to July 23, 2013 when MulticoreWare launched the pre-alpha code for the new x265 codec. Development of the x265 encoder had began as early as March 2013.

The main objective of the project was to make the x265 one of the best encoders in the industry. Currently, the project is funded by a group of top companies in return for exclusive rights to use the x265 converter in distribution of their products without the GPL 2 license. The source code for the x265 codec is done in C++ programming language.

x265 Encoder/Encoding

Technically, the current version of x265 encoder has a bit depth limitation of 8-bits per color. It does not use B-Frames in its default GOP structure and is recommended for use in a computer with 8 GB of RAM. Ideally, the computer should have the 64 Bit version of either Windows 7 or Windows 8. Another key requirement of the latest x265 version is a CPU that can effectively support Advanced Vector Extension. Most of the features in the previous x264 version are not supported in this new x265 encoder. Some of the unsupported features of the x264 include multi-pass encoding, rate control and lookahead features. A few other features of the previous version have remained unoptimized such as biprediction and weighted prediction functions.

x265 Encoder
(source: x265.org)


According to x265 codec developers, Multicore, the new version is expected to show a decrease in bit rate on the basis of peak signal-to-noise ratio or PSNR by up to 35% compared to the previous x264 version. Multicore states that coding efficiency in the x265 will bring about great improvements in the video encoder. For example, when recently compared with an ExtremeTech encoder, it took the x265 encoder 129 seconds to encode a clip on a preset status of very slow while the extremeTech took 247 seconds to encode the same video clip.

x265: The Future Of Video Encoding?

In terms of capabilities, the x265 converter comes with a command line interface and an API. The command line interface is mostly used by graphical user interface systems such MeGUI and Stazrip. The API is quite useful in many interfaces including FFmpeg and HandBrake. Key features in the x265 codec design include a tree-structured prediction system, wavefrongt processing structure, de-blocking filter, and many other techniques that are quite helpful in working with multi-pass encoding. Generally, the x265 codec incorporates many more helpful features than the H.264 encoders. The main idea behind the development of the x265 codec was to create an encoder that would allow the user to encode a video of a similar quality level as one encoded by the best software but at lower bit rates. The main objective was high quality at lower bit rates. The x265 encoder has improved coding efficiency in comparison with other popular video encoders which means it can reduce bit rate by half and still maintain image quality. The x265 codec provides advanced computational complexity, better compression rate, and a significant reduction in processing delay time.

x265 Cloud Video Encoding
(source: x265.org)


The x265 codec nicknamed H.265 ushers in a new standard in High performance Video Encoding. The ISO/MPEG project combines advanced computational efficiency with state-of-the-art video compression performance to provide high quality videos (such as 4K) at very low bit rates. It is however important to note that the creation of the x265 codec or the new H.265 standard has relied heavily on modifications of the previous H.264 design.


Post written by Eric Fontaine (@EricFontaine_)