About x265

x265 is the world’s most efficient HEVC encoding library, delivering the highest visual quality for any target bit rate.

x265 Visual Quality Algorithms

  • Look-Ahead (scene detection, slice type decisions)
  • Adaptive Quantization
  • Macroblock Tree (CU-tree)
  • B-Pyramid
  • B-Adapt
  • Weighted Prediction
  • Seven levels of Rate Distortion Optimization
  • Psycho-visual Rate Distortion Weighting
  • Psycho-visual Rate Distortion Optimized Quantization

Input Capabilities

  • Supports YUV or Y4M input
  • 4:4:4, 4:2:2, 4:2:0 or 4:0:0 chroma
  • 8 to 16 bits/color
  • Dither: higher quality downsampling
  • Noise Reduction
  • Interlace signaling
  • Custom scaling, lambda or QP file

Full HEVC Specification Support

  • Profiles:  Main, Main10, Main Still Picture
  • Tiers:  Main Tier or High Tier
  • Lossless Encoding, CU-Lossless
  • All HEVC resolutions
  • Level-IDC: minimum decoder level
  • VUI:  Specify Video Usability Information
  • SEI: Info, HRD, AUD, HASH

x265 Rate Control Modes

  • Constant QP
  • Constant Rate Factor
  • Average Bit Rate
  • 2 Pass encoding
  • N-pass encoding
  • Video Buffer Verification
  • Hypothetical Reference Decoder

Encoding Parameter Controls

  • Wavefront Parallel Processing
  • Max CTU Size
  • Min CU Size
  • Transform Unit Intra Depth
  • Transform Unit Inter Depth
  • Motion Search Method
  • Motion Search Range
  • Subpel Refinement Level
  • Maximum Number of Merge Candidates

Slice Decision Controls

  • RC-lookahead: # frames to look ahead
  • Open-gop: allow I-slices to be non-IDR
  • Keyint: Max intra period in frames
  • Min-keyint: Minimum GOP size
  • Scenecut: Insert I-frames at scene changes
  • B-adapt: Adaptive B frame scheduling
  • Bframes: Max # of consecutive b-frames
  • Bframe-bias: Bias towards B frames
  • B-pyramid: Use B-frames as references
  • Weighted P Frame Prediction
  • Weighted B Frame Prediction
  • Ref: Max number of L0 references

Encoding Parameter Controls

  • RD Penalty
  • B-Intra
  • Intra Transform Skip
  • Fast Intra Transform Skip
  • Strong Intra Smoothing
  • Constrained Intra Prediction
  • Rectangular Motion Partitions
  • Fast Coded Block Flag
  • Fast Intra Search
  • Sign Hiding
  • Cb chromaQP Offset
  • Cr chromaQP Offset
  • Loop Filter
  • Sample Adaptive Offset

Encoding Performance Features

  • Wavefront Parallel Processing
  • Frame Parallelism
  • Parallel Motion Estimation
  • Parallel Mode Decision
  • Highly optimized for the latest x86 SIMD instructions, including MMX2, SSE, SSE2, SSE3, SSSE3, SSE4, SSE4.1, SSE4.2, AVX, XOP, FMA4, AVX2, FMA3

x265 source code is available for developers who would like to contribute to the project, or build open-source applications under the terms of the GNU GPL v2 license.  Commercial licenses are available for companies who want to use x265 in video hardware and software products.

Download the x265 HEVC Upgrade!