SVT-AV1 vs x265: Compression Efficiency Compared

This article provides a direct comparison of the raw compression efficiency between the libsvtav1 (SVT-AV1) encoder and the x265 encoder. We analyze how these two prominent video encoders perform when balancing visual quality against file size, highlighting which codec delivers superior data savings and under what conditions.

Raw Compression Efficiency: The Bitrate Winner

In terms of pure compression efficiency—defined as the ability to maintain a target visual quality at the lowest possible bitrate—libsvtav1 consistently outperforms x265. Under standardized objective testing using metrics like VMAF (Video Multi-Method Assessment Fusion) and PSNR, libsvtav1 achieves significant data savings over x265.

On average, libsvtav1 delivers 15% to 30% bitrate savings compared to x265 for equivalent visual quality. This efficiency gap is most pronounced at lower bitrates and higher resolutions, such as 4K and 1080p, where the advanced coding tools of the AV1 standard can be fully leveraged.

Key Factors Driving SVT-AV1’s Superiority

Several architectural advantages allow libsvtav1 to surpass x265 in compression efficiency:

• Larger Block Sizes: AV1 supports Superblocks up to 128x128 pixels, whereas HEVC (x265) maxes out at 64x64. This allows libsvtav1 to compress homogeneous areas (like skies or flat backgrounds) much more efficiently.
• Advanced Intra and Inter Prediction: SVT-AV1 utilizes highly refined prediction angles and motion compensation tools, reducing the amount of residual data that needs to be encoded.
• Film Grain Synthesis: Instead of spending valuable bits trying to compress random film grain, libsvtav1 can analyze the grain, remove it during encoding, and synthesize it back on the decoder side. This tool alone drastically reduces the bitrate of noisy or cinematic content compared to x265.

The Complexity and Speed Trade-off

While libsvtav1 wins the raw compression battle, it historically required vastly more computational power to do so. However, recent optimization updates to the SVT-AV1 codebase have significantly narrowed this gap.

To achieve the maximum compression efficiency of libsvtav1 (using lower, high-quality presets like Preset 2 or 3), encoding times are still longer than equivalent high-efficiency presets in x265 (such as “Veryslow”). When libsvtav1 is tuned to match the encoding speed of x265, the efficiency gap narrows, but SVT-AV1 generally retains a slight edge in quality-per-bit.

Summary of Use Cases

• Choose libsvtav1 when bandwidth preservation, storage limits, and delivery costs are the primary concerns. It is the superior choice for high-volume streaming, archiving, and distribution.
• Choose x265 when encoding hardware is older, decoding compatibility across legacy devices is mandatory, or when you require extremely fast encoding speeds with mature, predictable software support.