HEVC / H.265 Video Codec: The Complete Technical Guide

What Is HEVC / H.265?

HEVC — High Efficiency Video Coding — is the video compression standard that succeeded H.264/AVC. Jointly developed by the ITU-T Video Coding Experts Group (VCEG) and the ISO/IEC Moving Picture Experts Group (MPEG) under the Joint Collaborative Team on Video Coding (JCT-VC), HEVC was finalized in 2013 and published as ISO/IEC 23008-2 and ITU-T H.265.

HEVC's defining achievement: equivalent visual quality to H.264 at approximately half the bit rate. This efficiency gain comes at the cost of dramatically higher computational complexity — HEVC encoding is 5–10× slower than H.264 at equivalent quality settings.

HEVC is the dominant codec for:

• 4K UHD streaming (Netflix, Disney+, Amazon Prime — all use HEVC for 4K)
• 4K Blu-ray discs (BDMV spec mandates HEVC for UHD Blu-ray)
• HEIF images (the still-image application of HEVC — default on Apple devices since iOS 11)
• Video surveillance (H.265 halves storage requirements)
• Broadcast TV (DVB-T2, ATSC 3.0, ISDB-T2 all support HEVC)

Key Improvements Over H.264

Larger Coding Unit (CTU vs. Macroblock)

H.264 uses 16×16 macroblocks. HEVC introduces the Coding Tree Unit (CTU) with a maximum size of 64×64 pixels. The CTU can be recursively split into smaller Coding Units (CU) down to 8×8, allowing the encoder to use large units for flat regions (one prediction for a 64×64 block) and small units for detail areas. This quadtree structure dramatically reduces overhead for high-resolution content.

Improved Intra Prediction

H.264 has 9 intra prediction directions. HEVC expands to 35 intra prediction directions (33 angular modes + planar + DC), allowing much better prediction of textured surfaces, diagonal edges, and complex patterns.

Advanced Motion Compensation

• Merge mode: inherit motion vectors from neighboring blocks without explicit signaling.
• Advanced TMVP: temporal motion vector predictor from previously encoded frames.
• Overlapped Block Motion Compensation (OBMC) (in some profiles).
• 1/4-pixel precision for luma, 1/8-pixel for chroma.

In-Loop Filters

HEVC adds two in-loop filters applied during encoding (which means reference frames are deblocked/denoised, improving prediction quality):

1. Deblocking filter: removes blocking artifacts at CTU boundaries.
2. Sample Adaptive Offset (SAO): reduces ringing artifacts by classifying samples and adding offsets — a novel addition not present in H.264.

HEVC Profiles

Main 10 is the dominant profile for consumer use — it is required for HDR10 content and supported by virtually all modern hardware decoders.

HEVC and HDR

HEVC is the first codec standardized alongside major HDR technologies:

• HDR10: HEVC Main 10, static metadata (MaxCLL, MaxFALL) via SEI messages.
• HDR10+: Dynamic metadata per scene (Samsung/Amazon).
• Dolby Vision: Dual-layer HEVC with BL (base layer) + EL (enhancement layer), or single-layer with RPU metadata.
• HLG (Hybrid Log-Gamma): BBC/NHK HDR system for broadcast.

HDR requires 10-bit encoding (Main 10 profile) to provide sufficient precision for the BT.2020 wide color gamut.

ffmpeg HEVC Encoding

# Software encode (libx265) — high quality, slow
ffmpeg -i input.mp4 -c:v libx265 -crf 28 -preset medium output.mp4

# Hardware encode — NVIDIA NVENC
ffmpeg -i input.mp4 -c:v hevc_nvenc -rc:v vbr -cq:v 28 output.mp4

# Hardware encode — Intel QSV
ffmpeg -i input.mp4 -c:v hevc_qsv -global_quality 25 output.mp4

# Hardware encode — Apple VideoToolbox (macOS)
ffmpeg -i input.mp4 -c:v hevc_videotoolbox -q:v 60 output.mp4

# 4K HDR10 encoding
ffmpeg -i input.mkv \
  -c:v libx265 -crf 20 -preset slow \
  -x265-params "hdr-opt=1:repeat-headers=1:colorprim=bt2020:transfer=smpte2084:colormatrix=bt2020nc:master-display=G(13250,34500)B(7500,3000)R(34000,16000)WP(15635,16450)L(10000000,50):max-cll=1000,400" \
  -c:a copy output_hdr10.mkv

# Convert H.264 to HEVC (quality-preserving transcode)
ffmpeg -i input_h264.mp4 -c:v libx265 -crf 24 -preset medium -c:a copy output_hevc.mp4

CRF Values for libx265

HEVC Licensing: The Patent Minefield

HEVC's biggest practical problem is its patent licensing situation. Three patent pools and numerous individual licensors claim essential patents:

• HEVC Advance: ~USD 0.60 per device, or 0.2% of revenue
• Velos Media: additional license required
• Via LA: another pool with different terms
• Individual licensors: Qualcomm, Sisvel, others

This fragmentation led many companies to seek HEVC-free alternatives, driving adoption of AV1.

HEVC Container Formats

HEVC is typically stored in:

• HEVC Annex B (.hevc, .265): raw bitstream, used in broadcasting
• MP4/ISOBMFF (.mp4, .m4v): standard web and consumer container
• Matroska (.mkv): preferred for archiving and PC playback
• MPEG-TS (.ts, .m2ts): broadcast and Blu-ray
• MOV (.mov): Apple's container

HEVC vs. H.264 vs. AV1

Best Practices

1. For 4K/HDR content, HEVC (Main 10) is the current standard — all streaming platforms and UHD Blu-ray use it.
2. Use CRF 24–28 with libx265 for a good quality/size balance.
3. Use hardware encoders (NVENC, QSV, VideoToolbox) for real-time or near-real-time encoding.
4. Use software encoder (libx265) for archiving — better quality at same file size.
5. Use .mkv container for HEVC archives — MKV handles HEVC streams cleanly.
6. For HDR10, set correct metadata (MaxCLL, MaxFALL, mastering display) for proper tone mapping.
7. For 1080p and below, consider AV1 or H.264 — HEVC licensing costs may not be justified.
8. Preset slow or slower gives ~10–15% better compression than medium at significant time cost.
9. Use --pools flag in x265 to control thread usage on multicore systems.
10. For broadcast, use HEVC Annex B in MPEG-TS containers with the appropriate profile level tier.

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