H.264 vs H.265: Interactive Comparison

Codec Specifications at a Glance

H.265/HEVC (2013) was designed to halve the bitrate of H.264/AVC (2003) at equivalent visual quality.

Feature	H.264 / AVC	H.265 / HEVC
Year standardized	2003	2013
Block unit	16×16 Macroblock (fixed)	Up to 64×64 CTU (Coding Tree Unit, adaptive)
Min block size	4×4	4×4
Transform sizes	4×4, 8×8	4×4, 8×8, 16×16, 32×32
Intra prediction modes	9 modes	35 modes (33 angular + DC + Planar)
Max resolution	4096×2304	8192×4320 (8K)
Bitrate efficiency	Baseline	~40–50% more efficient
Encoding complexity	Low	5–10× higher
Hardware decode support	Near-universal	Widespread (2015+ devices)
Patent licensing	Single pool (MPEG LA)	Multiple competing pools

Adaptive Block Partitioning

H.264 slices every frame into uniform 16×16 macroblocks. H.265 starts with 64×64 CTUs and recursively splits complex regions down to 4×4 — large blocks for smooth areas save bits, small blocks preserve fine detail.

How to read this: Both canvases show the same test image with block boundaries overlaid. H.264 uses a rigid grid — every region gets the same block size regardless of complexity. H.265 uses large blocks (green) where content is smooth, and small blocks (red) where detail is high. Adjust the split threshold to see how the encoder trades quality for efficiency.

Image:

H.265 split sensitivity: 50

H.264 — Uniform 16×16 Macroblocks

H.265 — Adaptive CTU Partitioning

H.265 block sizes:

64×64 (smooth)

32×32

16×16

8×8

4×4 (complex)

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H.264 blocks (16×16)

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H.265 leaf blocks

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Block count reduction

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Avg H.265 block size

Intra Prediction Modes

Intra prediction estimates pixel values from already-decoded neighbors. The encoder picks the best mode and only stores the difference (residual). More angles = better predictions = smaller residuals = fewer bits.

H.264 has 9 intra prediction modes: DC (flat average), Planar-like, and 7 directional. H.265 expands this to 35 modes: DC, Planar, and 33 angular directions spanning 180°. Hover over arrows to identify each mode.

Compression Quality Simulator

Both codecs are simulated using DCT-based compression. H.264 uses fixed 8×8 blocks. H.265 uses adaptive block sizes — larger in smooth regions, smaller in complex ones. At the same quality setting, H.265 produces fewer non-zero DCT coefficients (fewer bits).

What to look for: At low quality (left side of slider), H.264's 8×8 block boundaries become visible as a grid pattern. H.265's larger blocks in smooth areas avoid this artifact. The PSNR and bit count show the efficiency gain quantitatively.

Image:

Quality: 6

H.264 (8×8 DCT blocks)

PSNR: — Bits: —

H.265 (Adaptive DCT blocks)

PSNR: — Bits: —

Original (uncompressed)

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H.265 PSNR gain

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Bit savings (H.265)

When to Use Each Codec

Both codecs remain widely deployed. The right choice depends on delivery target, hardware, and encoding constraints.

Use H.264 when…

Maximum compatibility is needed (legacy devices, all browsers, smart TVs)
Fast or real-time encoding (live streaming, video calls, WebRTC)
Content is 1080p or below with adequate bandwidth
Licensing simplicity matters (single MPEG LA patent pool)
Target includes older hardware decoders pre-2015
Encoding cost must be minimized

Use H.265 when…

Delivering 4K or 8K content where bandwidth is the constraint
Targeting modern devices (2015+) with HEVC hardware decode
Storage efficiency is critical (archives, VOD libraries)
HDR / wide color gamut content (HDR10, HLG, Dolby Vision)
Encoding is offline and latency is not a concern
Apple ecosystem (all Apple Silicon devices decode H.265 in hardware)

Looking further ahead: AV1 is a royalty-free codec with efficiency comparable to H.265 and growing hardware support. For new web deployments, AV1 (with VP9 fallback) avoids H.265's patent pool fragmentation. H.266/VVC (2020) offers another ~50% over H.265 but has minimal deployment today.