Apply blur to a region of the video
video filters
// what it does
This graph censors a fixed region. `split` duplicates the stream into `[original]` and `[copy]`; the copy is cropped to a 200x200 patch at offset (100,100) via `crop=200:200:100:100`, blurred with `boxblur=10`, then `overlay=100:100` pastes that blurred patch back exactly where it was cut. It's the standard recipe for masking a face, license plate, or on-screen ID in a stationary area.
// shell
$ ffmpeg -i input.mp4 -vf "split[original][copy];[copy]crop=200:200:100:100,boxblur=10[blurred];[original][blurred]overlay=100:100" output.mp4// gotcha
The crop offset and the overlay position must match (both 100:100 here) or the blurred patch lands in the wrong spot. Because the region is fixed, anything that moves out of that rectangle stops being covered — this doesn't track a subject.