libsvtav1 vs libvpx-vp9 Visual Quality Comparison

This article provides a direct comparison of the subjective visual quality of the libsvtav1 (AV1) encoder against the older libvpx-vp9 (VP9) encoder. We examine how the architectural differences between these two codecs impact real-world viewing experiences, focusing on compression artifacts, texture preservation, and bitrate efficiency.

Visual Quality at Equivalent Bitrates

When comparing both encoders at the same bitrate, libsvtav1 consistently outperforms libvpx-vp9 in subjective visual quality. On average, libsvtav1 achieves a 20% to 30% reduction in file size while maintaining a visual experience identical to or better than libvpx-vp9. At lower bitrates, where codecs are pushed to their limits, libvpx-vp9 begins to show significant degradation, whereas libsvtav1 maintains structural integrity and image clarity.

Blockiness and Color Banding

One of the most noticeable differences in subjective quality is how each encoder handles flat surfaces and dark scenes:

• libvpx-vp9: Under low-to-medium bitrate constraints, VP9 often introduces blockiness (where the macroblock boundaries become visible) and severe color banding in gradients, such as skies or shadows.
• libsvtav1: SVT-AV1 utilizes more advanced partition sizes (up to 128x128 pixels) and sophisticated deblocking filters. This allows it to smoothly render gradients and dark scenes, virtually eliminating blockiness and greatly reducing banding.

Fine Detail and Texture Retention

libsvtav1 excels at preserving high-frequency details like hair, skin texture, grass, and water ripples. libvpx-vp9 tends to apply a heavy smoothing effect to these complex areas to save bitrate, which results in a soft, muddy, or “plastic” appearance. SVT-AV1’s superior intra-prediction and chroma-from-luma tools allow it to compress complex textures without sacrificing the sharpness that human eyes naturally look for.

Film Grain Synthesis

A major subjective advantage of libsvtav1 is its support for Film Grain Synthesis. In traditional encoders like libvpx-vp9, organic film grain is treated as high-frequency noise and is either completely wiped out or consumes an enormous amount of bitrate to encode.

libsvtav1 solves this by removing the grain during the encoding process, sending the grain parameters as metadata, and reconstructing the grain on the decoder side. This results in a picture that looks naturally cinematic and sharp, without the massive bitrate penalty that VP9 would require to achieve the same effect.