Mosaic versus blur for hiding a face
Mosaic divides the face into blocks and fills each block with its average colour; with 16 px blocks a 1080p face becomes a dozen flat tiles and no expression survives. Blur keeps a soft silhouette and looks less obtrusive, but a very light blur leaves recognisable shapes. Both are set per video here, and any manual region keeps the method it was created with, so you can pixelate most faces and black out one.
A mosaic reads unmistakably as "censored", which is often what news, documentary and complaint footage needs: viewers understand the face was hidden on purpose.
Choosing the block size
The strength slider is the block edge in pixels of the output video. 8 px is subtle, 16 px (default) is the usual broadcast look, 32–64 px is a coarse grid for faces that fill the frame. Blocks are measured on the full-resolution output, so a 4K video needs roughly twice the block size of 1080p for the same look.
Research on de-pixelation shows that tiny blocks over a known set of faces can be partly reversed; large blocks or Solid cover are the safe choice when the subject must not be identifiable.
Keeping the mosaic on a moving face
Faces are tracked frame by frame, and the mosaic follows the confirmed outline with the padding you set. Where tracking is uncertain the timeline shows an orange review section; play it and, if the mosaic lags or drops, draw a manual rectangle and add a keyframe at the start and end of the movement.
The sound track is copied unchanged, so the result is the original clip with mosaics — nothing else altered.
Formats and limits
Input is MP4 with H.264 or HEVC video (iPhone MP4s included if the browser can decode HEVC), up to 5 minutes, 500 MB, 4K and 30 fps; output is H.264 MP4 without the original's metadata. Chrome or Edge on a computer is required; Android Chrome works with lower limits.