librav1e Default Settings: Speed vs File Size

This article explains how the default configuration of librav1e—the library version of the rav1e AV1 encoder—balances encoding speed and output file size. We will examine the default speed presets, rate control mechanisms, and how these settings position librav1e as a balanced tool for AV1 video encoding.

librav1e relies on a set of default parameters designed to offer a middle-ground experience out of the box, preventing excessively long encoding times while still leveraging the high compression efficiency of the AV1 format. The two primary settings that govern this balance are the speed preset and the quantizer (quality) level.

The default speed preset in librav1e is set to 6 (on a scale from 0 to 10, where 0 is the slowest with the best compression, and 10 is the fastest with the worst compression). Preset 6 serves as the standard baseline because it disables some of the most computationally expensive encoding tools—such as exhaustive partition searches and complex motion estimation—while keeping essential AV1 features active. This results in an encoding process that is significantly faster than the archival-grade presets (0–4) but still delivers a file size that is noticeably smaller than legacy codecs like H.264 at equivalent quality.

In terms of file size and quality, librav1e defaults to a Constant Quality (CQ) mode with a default quantizer parameter (QP) of 100 (on a scale of 0 to 255). This default quantizer strikes a deliberate compromise. It is low enough to prevent obvious visual compression artifacts, yet high enough to keep the bitrate within a reasonable range.

By pairing Speed 6 with a Quantizer of 100, librav1e achieves a practical equilibrium. Users receive a reasonably compact file without having to wait hours for a short video clip to render. If your workflow prioritizes smaller file sizes above all else, you must manually lower the speed preset (e.g., to 4 or 3), which exponentially increases encoding time. Conversely, if fast delivery is your priority, increasing the speed preset toward 10 will reduce encoding times but will result in larger file sizes to maintain the same level of visual quality.