H.265/HEVC Video Codec: Complete Guide to High Efficiency Video Coding

What Is H.265/HEVC?

H.265, also known as HEVC (High Efficiency Video Coding) and MPEG-H Part 2, is the successor to H.264. Published jointly by the ITU-T and ISO/IEC in 2013, HEVC achieves approximately 50% better compression efficiency than H.264 — it can deliver the same video quality at half the bitrate, or significantly better quality at the same bitrate.

HEVC powers:

• 4K Ultra HD Blu-ray discs (the only disc format capable of 4K at acceptable quality)
• 4K and 8K streaming on Netflix, Amazon Prime, Disney+, Apple TV+
• HEIC photos (Apple's iPhone photo format uses HEVC for image compression)
• HDR video (HDR10, HDR10+, HLG — all use HEVC's Main 10 profile)
• Broadcast (DVB-T2, ATSC 3.0 / NextGenTV, DAB+)

HEVC vs H.264: Key Technical Improvements

HEVC builds on H.264's foundation while introducing significantly more powerful tools:

Larger Block Structure: CTUs

H.264 uses fixed 16×16 macroblock units. HEVC replaces these with flexible Coding Tree Units (CTUs) of up to 64×64 pixels. CTUs are recursively split into smaller Coding Units (CUs) — 64×64, 32×32, 16×16, or 8×8 — using a quadtree structure based on image complexity.

This adaptive block size is transformative for high-resolution video: a 4K frame has large areas of uniform content (sky, walls) where a 64×64 block can be coded efficiently, and fine-detail areas where smaller blocks capture texture. H.264's fixed 16×16 macroblocks waste bits in smooth areas and lack precision in detail areas.

More Intra Prediction Modes

H.264 has 9 intra prediction modes for 4×4 luma blocks. HEVC has 35 intra prediction modes including 33 directional modes, a DC mode, and a planar mode. This finer-grained prediction drastically reduces residual energy for structured content like text, graphics, and detailed textures.

Improved Inter Prediction

• Larger reference frame cache — more flexibility in temporal prediction
• Advanced Motion Vector Prediction (AMVP) — more efficient motion vector coding
• Merge mode — sharing motion vectors from neighboring blocks without signaling new vectors
• Asymmetric Motion Partitioning (AMP) — non-square partition options for better object boundary prediction

Sample Adaptive Offset (SAO) Filter

HEVC adds SAO as a second in-loop filter (complementing the deblocking filter, which also improved from H.264). SAO reduces banding artifacts in smooth gradients and ringing near edges — common artifacts at lower bitrates.

Transform Options

• 4×4, 8×8, 16×16, and 32×32 DCT transforms (H.264 maxes out at 8×8)
• 4×4 DST (Discrete Sine Transform) for intra-coded residuals — more efficient than DCT for intra prediction residuals

CABAC Improvements

HEVC's CABAC entropy coder is more efficient than H.264's and redesigned for better parallelism, enabling multi-threaded encoding and decoding through:

• Tiles — rectangular regions that can be decoded independently
• Slices — independently decodable segments
• Wavefront Parallel Processing (WPP) — pipeline-based parallelism

HEVC Profiles

Main 10 is the most important profile — it powers all 4K HDR consumer content (Netflix 4K HDR, Ultra HD Blu-ray, Apple TV 4K, YouTube HDR).

HEVC and HDR

HEVC Main 10 profile (10-bit color depth) is the technical foundation for HDR video:

HDR10

• Static HDR metadata (MaxCLL, MaxFALL) — same metadata for entire film
• SMPTE ST 2084 (PQ — Perceptual Quantizer) transfer function
• BT.2020 color space (wide color gamut)
• Open standard, royalty-free
• Supported by: all 4K HDR displays, Ultra HD Blu-ray, most streaming services

HDR10+

• Dynamic HDR metadata — scene-by-scene or frame-by-frame tone mapping
• Same PQ + BT.2020 as HDR10 but adds Samsung SMPTE ST 2094-40 dynamic metadata
• Supported by Samsung TVs, Amazon Prime Video

HLG (Hybrid Log-Gamma)

• Designed for broadcast TV (NHK, BBC developed jointly)
• Backward compatible with SDR displays (non-HDR TVs show correct SDR image from HLG signal)
• Used in terrestrial HDR broadcasts, some streaming

HEVC Encoding with x265

x265 is the primary open-source HEVC encoder.

# CRF 28 (roughly equivalent to x264 CRF 23)
ffmpeg -i input.mp4 -c:v libx265 -crf 28 -preset medium output.mp4

# High quality master (CRF 18)
ffmpeg -i input.mp4 -c:v libx265 -crf 18 -preset slow output.mp4

# 4K HDR10 encoding
ffmpeg -i input.mp4 -c:v libx265 -crf 20 -preset slow \
  -x265-params "colorprim=bt2020:transfer=smpte2084:colormatrix=bt2020nc:hdr10=1:max-cll=1000,400:master-display=G(13250,34500)B(7500,3000)R(34000,16000)WP(15635,16450)L(10000000,50)" \
  -pix_fmt yuv420p10le -c:a copy output.mp4

# HEVC with Main 10 profile (10-bit, for wide color)
ffmpeg -i input.mp4 -c:v libx265 -crf 20 -pix_fmt yuv420p10le \
  -x265-params "profile=main10" output.mp4

x265 CRF Calibration

x265 CRF values are not directly comparable to x264 CRF values. A rule of thumb:

• x265 CRF 28 ≈ x264 CRF 23 (similar visual quality, smaller file)
• x265 CRF 24 ≈ x264 CRF 19
• x265 CRF 20 = very high quality for HEVC

For a given quality level, x265 produces files approximately 50% smaller than x264.

HEVC Patent Licensing

HEVC has a complex and fragmented patent licensing landscape involving multiple patent pools:

• HEVC Advance — covers ~4,000 patents from 40+ companies
• Via LA HEVC — covers patents from Dolby, GE, Philips, etc.
• Velos Media — covers additional patents

Royalties apply to encoders, decoders, and content distribution in some interpretations. This patent complexity partly drove the development of AV1 as a royalty-free alternative. However, hardware support for HEVC is nearly universal in modern devices, and the practical impact of patent fees on end users and open-source software has been limited.

HEVC Hardware Support

Nearly all devices manufactured after 2015 have dedicated HEVC hardware decode support:

Hardware encoding is much faster than software (x265) but generally lower quality at the same bitrate.

H.264 vs. H.265 vs. AV1 Comparison

Practical recommendation:

• Archive storage: HEVC (50% smaller than H.264 at same quality)
• Web streaming: H.264 for maximum compatibility; AV1 for bandwidth savings on modern browsers
• 4K HDR content: HEVC (hardware support is universal)
• Professional production: Apple ProRes or HEVC Main 10

Related conversions

Common video conversions that pair well with this guide:

• MOV to MP4
• AVI to MP4
• MKV to MP4
• MP4 to WEBM
• MP4 to GIF
• MP4 to MP3