computer science

X265

X265 is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand X265 rather than just read about it. In short: x265 is an encoder for creating digital video streams in the High Efficiency Video Coding (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, under the terms of GNU General Public License (GPL) version 2 or later; however, customers may request a commercial license.

Key takeaways

X265 belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect X265 to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of X265 from memory before moving on to harder problems.

Reference excerpt

x265 is an encoder for creating digital video streams in the High Efficiency Video Coding (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, under the terms of GNU General Public License (GPL) version 2 or later; however, customers may request a commercial license.

History x265 builds on source code from x264, 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 and its now defunct 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 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 (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, 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. 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.

Open-source adopters Open source software projects which utilize x265 for HEVC encoding:

Avidemux FFmpeg HandBrake Internet Friendly Media Encoder MeGUI OpenShot ShareX 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

Illustrations

Worked examples

Example 1 — a first encounter with X265

Start with the simplest possible case. Write down what X265 claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to X265 before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about X265 ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of X265

In research: X265 appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses X265 in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: X265 is common in secondary-school and first-year university syllabi. It links to neighbouring topics C++ libraries, Computer file formats, Free software programmed in C++, so understanding it makes those chapters shorter.
In everyday life: Look for X265 outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “X265” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study X265 in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what X265 means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain X265 out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is X265 in simple terms?

Why does X265 matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study X265?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on X265.