Blur a moving object in a video

How to blur something that moves in a video

1. 1

   Load the footage

   Drop the clip into the tool above or pick it from your device. Then choose Blur, Pixelate or Black box as the effect.

2. 2

   Cover the object

   Switch to Chosen areas, pause on a frame where the object is sharp and fully in view, and drag a box over it. Pick Oval if the object is round.

3. 3

   Track it

   Select Track movement automatically. The cover is followed both ways from the playhead, and a note under the button says how far it got.

4. 4

   Fix and export

   If the note says it lost the object, jump to that time, drag the cover back on and select Track again from here. Scrub through once more, then select Export video.

What the tracker follows, and how

Track movement automatically has no idea what a car or a logo is. It takes the middle of your box as a small grayscale picture and, in each later frame, searches the nearby area for the spot that matches it best. Because only the middle is used, a box drawn a little loose around the object does no harm.

It checks about 12 moments every second and saves each position it finds, and the cover glides between them. Each step also tries the box slightly larger and slightly smaller, so a car driving toward the camera or a phone lifted closer can grow without escaping the cover.

While the match is strong, the tracker slowly refreshes its picture of the object, which helps with gradual changes in light or angle. It also expects the object to keep heading in roughly the same direction, so a steady pan or a car at constant speed is easy to follow.

When tracking loses the object

The tracker gives up when it cannot find a good match for a few samples in a row. Rather than guess, it stops and reports the time. These are the usual causes:

• The object leaves the frame or goes behind something, such as a car passing behind a bus.
• It jumps a long way between frames, as in a fast whip pan or a ball thrown across the shot.
• Its appearance changes suddenly, for example a person spinning round or a screen switching from dark to bright.
• It has little detail of its own, like the plain side of a white van, so there is nothing distinctive to match.
• A similar object sits right beside it. Matching uses brightness patterns rather than color, so two objects that differ mainly in color can look alike to it.

After the last position it saved, the cover stays where it was, so it may sit over empty background while the real object carries on. Go to the time in the message, drag the cover back onto the object and select Track again from here. The new run replaces only the stretch it covers and keeps the positions you already had either side.

If the object really does leave the shot, press Ends here at that moment so the cover disappears with it. Tracking never runs past an area's start and end times, which also stops it wandering onto something else.

Placing the cover by hand

Some movement is easier to set yourself than to track, such as a shot full of lookalikes or a stretch where the object is half hidden. Turn on Follow movement for the selected area, pause at a moment where the object has moved, and drag the cover onto it. Each drag at a new moment adds a position, and the cover slides in a straight line from one position to the next.

A few well-chosen positions are often enough: one where the movement begins, one where it changes direction and one where it ends. The number of saved positions shows under the switch, and Clear positions resets the area to a single spot.

After an automatic run, Follow movement is already switched on, so you can correct the tracked path the same way. Pause on the frame where the cover drifted and drag it back; that position is replaced, or a new one is added if none was saved there.

Tips for common moving objects

• Cars. To hide a whole car, box the car. To hide only its plate, box the plate on its own and track it as a separate area; the license plate guide has more on dashcam clips.
• Logos on clothing. Fabric folds and the print bends as the wearer moves, so check the cover around turns and arm swings. A box a little wider than the logo keeps its edges hidden when it shifts.
• Phone and laptop screens. A display whose content changes quickly is hard to match, so draw the box large enough to take in the device's edges as well. For readable text, Black box is the safer effect.
• People walking. For a face, find faces automatically rather than tracking one by hand. For a figure seen from behind, box the head and torso, since swinging arms and legs offer the tracker little that stays the same.

Each object needs its own area, tracked on its own. Add an area, place it, track it, then move on to the next; every area keeps its own positions and times, so a car crossing early and a cyclist arriving later do not interfere.