Configure rav1e Quantizer in FFmpeg

This article provides a quick guide on how to configure the quantizer parameter in the rav1e AV1 encoder using FFmpeg. You will learn the correct command-line syntax, the range of quantizer values, and how to balance video quality against file size.

Understanding the rav1e Quantizer

The rav1e encoder uses a quantizer parameter (QP) to control the compression level and overall quality of the output video. Unlike some encoders that use a 0–51 scale, rav1e uses a scale of 0 to 255.

• 0: Lossless (maximum quality, extremely large file size).
• 255: Maximum compression (lowest quality, smallest file size).
• Default: If not specified, the encoder typically defaults to a balanced mid-range value (often around 100).

A lower quantizer value results in higher visual fidelity but a larger file size, while a higher value reduces file size at the cost of visual clarity.

How to Set the Quantizer in FFmpeg

In FFmpeg, you can configure the rav1e quantizer using either the -qp option or the -crf option. The librav1e wrapper in FFmpeg treats both of these options similarly for constant quality encoding.

Standard Command Syntax

To set the quantizer, use the following command structure:

ffmpeg -i input.mp4 -c:v librav1e -qp 100 output.mp4

Alternatively, you can use -crf:

ffmpeg -i input.mp4 -c:v librav1e -crf 100 output.mp4

Recommended Quantizer Values

Because the scale ranges up to 255, the values differ significantly from encoders like libx264 or libsvtav1. Use these ranges as a starting point:

• High Quality (Archival): 50 – 80
• Standard/Medium Quality (Recommended): 80 – 120
• Low Quality (High Compression): 150 – 200

Combining Quantizer with Speed Presets

The speed of the rav1e encoder can be adjusted using the -preset option, which ranges from 0 (slowest, best compression efficiency) to 10 (fastest). For best results, pair your quantizer setting with an appropriate preset:

ffmpeg -i input.mp4 -c:v librav1e -qp 90 -preset 5 output.mp4