How to Use the FFmpeg Boxblur Filter

This article provides a straightforward guide on how to use the boxblur filter in FFmpeg to apply blurring effects to video files. You will learn the syntax of the filter, understand its key parameters—such as radius and power for luma, chroma, and alpha channels—and see practical command-line examples to easily apply these effects to your projects.

Understanding Boxblur Parameters

The boxblur filter in FFmpeg accepts six primary parameters. These parameters are grouped by video component: luma (brightness/grayscale), chroma (color), and alpha (transparency).

• radius (r): Defines the size of the blur area in pixels. A larger radius results in a stronger blur.
• power (p): Defines how many times the blur filter is sequentially applied. A higher power creates a smoother gradient blur but requires more processing power.

The basic syntax for the filter is: boxblur=luma_radius:luma_power:chroma_radius:chroma_power:alpha_radius:alpha_power

You can also use the abbreviated parameter names: * lr / lp (Luma radius / power) * cr / cp (Chroma radius / power) * ar / ap (Alpha radius / power)

Practical FFmpeg Boxblur Examples

Below are standard command-line examples showing how to apply the boxblur filter to a video named input.mp4.

1. Apply a Simple Blur to the Entire Video

To blur both the details (luma) and colors (chroma) of a video, you can set the radius to 10 and the power to 2 for both components:

ffmpeg -i input.mp4 -vf "boxblur=lr=10:lp=2:cr=10:cp=2" output.mp4

Alternatively, you can use the short-hand positional notation:

ffmpeg -i input.mp4 -vf "boxblur=10:2:10:2" output.mp4

2. Apply a Heavy Blur

If you want a highly obscured, dream-like effect, increase both the radius and the power settings:

ffmpeg -i input.mp4 -vf "boxblur=lr=30:lp=5:cr=30:cp=5" output.mp4

3. Blur Only the Details (Keep Color Intact)

By applying the blur only to the luma channel and keeping the chroma settings at 0, you can blur the details of the video while preserving the original color boundaries:

ffmpeg -i input.mp4 -vf "boxblur=lr=15:lp=3:cr=0:cp=0" output.mp4

4. Using Expressions for Dynamic Radius

FFmpeg allows you to use mathematical expressions for the radius. For example, you can set the blur radius based on the video width (w) or height (h). The following command sets the luma radius to 2% of the video’s width:

ffmpeg -i input.mp4 -vf "boxblur=lr=w*0.02:lp=2" output.mp4