Mosaic / Blur Region Tool

Apply mosaic (pixelize) or blur to a rectangular region of a video. Drag the box to position, resize at corners.

Local processing — no upload

🟦

Drop a video, or tap to select

MP4 / MOV / WebM

Preview (drag to move; corner handles to resize)

Tip: position the rectangle over a face, name tag, license plate, etc.

Effect

Strength

Limit to a time range (otherwise applied to whole clip)

Start (sec)

End (sec)

The rectangle is fixed throughout the clip (no face tracking). For moving subjects, run the tool multiple times on different time ranges.

Processing… 0%

Download masked video

Popular uses

Hide faces or platesProtect screen-share detailsBlur selected areas

Next tools

Crop Video Tool Video Compressor Video Watermark Tool

What this tool does

Drag a rectangle on the preview to choose the region
Mosaic (pixelate) / Gaussian blur / black-bar effects
Adjustable strength (mosaic block size, blur sigma)
Optional time range so the effect only applies to a portion
Local processing — sensitive footage stays on your device

How to use

1
Drop the video
MP4 / MOV / WebM containing the region you want to hide.
2
Drag to select a region
On the preview, drag a rectangle over the area you want to mask.
3
Pick effect and strength
Mosaic (pixelated) for emphatic privacy, blur for natural-looking masking, black-bar for full redaction.
4
Set a time range (optional)
When the info only appears briefly, target just those seconds.
5
Burn it in
Download once processing completes.

What each setting means

Region

Rectangle drawn on the preview, defining which pixels are masked.

Effect

Mosaic (block-style pixelation), Gaussian blur, or solid black bar.

Strength

Mosaic: how aggressively the region is downscaled. Blur: sigma value.

Time range

Off = whole video, on = effect only inside the chosen range.

Recommended settings

Hide faces before posting to YouTube

Mosaic · strong · whole video

Mosaic visibly signals “redacted” to viewers.

Blur a license plate

Gaussian blur · medium · whole video

Blur preserves the look of the scene while making text unreadable.

Redact confidential info

Black bar · whole video

Total occlusion when redaction is non-negotiable.

Hide info that flashes briefly

Time range on for 1–3 seconds · mosaic

Avoid masking longer than necessary.

Common pitfalls

Symptom: Subject moves outside the masked area

Cause: The mask is a static rectangle on every frame.

Fix: Split the masked region by time range, or use desktop FFmpeg with vidstab + facedetect for tracking.

Symptom: Mosaic looks too coarse

Cause: Strength is at maximum.

Fix: Drop strength to medium or low.

Symptom: Mask is offset from the target

Cause: Preview/source resolution mismatch.

Fix: Reload the video and re-drag the region after the preview renders correctly.

Equivalent FFmpeg commands

Reference commands you can run on the desktop FFmpeg CLI.

Mosaic a rectangular region

ffmpeg -i input.mp4 -filter_complex "[0:v]crop=200:120:100:50,scale=20:12,scale=200:120:flags=neighbor[m];[0:v][m]overlay=100:50" out.mp4

Pixelates a 200×120 region at (100,50) to 1/10 resolution and scales back.

Gaussian blur on a region

ffmpeg -i input.mp4 -filter_complex "[0:v]crop=200:120:100:50,boxblur=10:1[m];[0:v][m]overlay=100:50" out.mp4

Time-gated effect (5–10 sec only)

ffmpeg -i input.mp4 -filter_complex "[0:v]crop=200:120:100:50,boxblur=10:1[m];[0:v][m]overlay=100:50:enable='between(t,5,10)'" out.mp4

Browser support & limits

Recommended max: 500 MB
One region per pass — re-run for additional regions
No automatic subject tracking

Privacy

This tool runs ffmpeg.wasm directly in your browser. Files never leave your device — everything runs locally. Read the privacy policy →

Frequently asked questions

Does it auto-track moving subjects?

No — the mask is a static rectangle. Use desktop FFmpeg + facedetect or vidstab if you need tracking.

Can I mask multiple regions at once?

One region per pass. Send the output back through the tool for additional regions.

Mosaic vs. blur — which protects privacy?

Mosaic communicates redaction more visibly. Blur looks more natural but can occasionally be reversible at low sigma values. Use mosaic for privacy and blur for stylized scenes.

Is full black-bar redaction reversible?

No — the original pixels in that region are completely overwritten.

How strong should the blur be?

For unreadable text, sigma ≥ 15. For stylistic blur, 5–10 is typical.

Will weak mosaic still hide faces?

Weak mosaic preserves enough structure for re-identification. Use medium or strong settings for true privacy.