librav1e vs x265: Perceptual Quality Comparison

This article compares the librav1e AV1 encoder and the x265 HEVC encoder when targeting equivalent perceptual quality. We analyze their compression efficiency, encoding speed, computational demands, and practical use cases to help you determine the best encoder for your video delivery needs.

Compression Efficiency and Bitrate Savings

When targeting equivalent perceptual quality—typically measured by metrics like VMAF (Video Multi-Method Assessment Fusion) or SSIM (Structural Similarity)—librav1e generally outperforms x265.

Because librav1e utilizes the AV1 coding standard, it can achieve the same visual quality as x265 (HEVC) at a significantly lower bitrate. On average, AV1 provides a 15% to 30% reduction in file size compared to HEVC for equivalent perceptual quality. This advantage is most pronounced at lower bitrates, where librav1e maintains image block integrity and avoids the blocking artifacts that can become visible in x265 encodes.

Encoding Speed and Performance

While librav1e wins on compression efficiency, x265 is the clear winner regarding encoding speed and computational efficiency.

• x265 is a highly mature encoder written in C++ with extensive assembly-level optimizations (such as AVX2 and AVX-512). It processes video quickly, making it suitable for real-time encoding and high-throughput workflows.
• librav1e is written in Rust and is designed to be a safe, fast, and lightweight AV1 encoder. However, because the AV1 standard is fundamentally more complex than HEVC, encoding with librav1e requires significantly more CPU cycles. Even at its fastest speed presets, librav1e is considerably slower than x265 at comparable quality-preserving presets.

Resource Utilization

To achieve equivalent perceptual quality, librav1e requires a much higher investment in hardware resources. Encoding a video with librav1e will result in longer rendering times and higher CPU utilization. For organizations with limited computing budgets or tight delivery deadlines, x265 offers a much more economically viable path to high perceptual quality. Conversely, if storage costs and distribution bandwidth are your primary expenses, the CPU investment required by librav1e is justified by the resulting bandwidth savings.

Licensing and Ecosystem Support

The choice between these two encoders also depends on your target audience and distribution platforms:

• Licensing: AV1 (librav1e) is fully open-source and royalty-free. HEVC (x265) is subject to complex licensing terms and patent pools, which can carry royalty fees for commercial distributors.
• Compatibility: x265 (HEVC) enjoys widespread hardware decoding support across almost all modern smartphones, smart TVs, and PCs. While AV1 hardware decoding is standard in newer devices, older hardware must rely on software decoding, which can drain the battery on mobile devices.