Fixing jelly wobble with rolling shutter repair

Pan a phone camera quickly past a building and the walls may lean like they are melting. Shoot from a car or a drone and the picture may wobble like jelly. That is rolling shutter, and it comes from how most phone and action camera sensors work. Video by Zaweba has a rolling shutter repair effect, found in the Clip menu as a distort effect, that measures the movement and puts the rows of the picture back where they belong.

Why rolling shutter happens

Many camera sensors don't capture the whole frame in one instant. They read it out row by row, usually from top to bottom. The bottom row is read slightly later than the top. If the camera or the subject moves during that short time, each row captures the scene at a slightly different moment. Straight vertical lines lean, spinning propellers bend, and vibration turns into a wobbly, jelly look.

The faster the movement and the slower the readout, the worse it gets, which is why fast pans on phones show it most.

How the repair works

The effect measures how the picture moves on each frame. Knowing that movement, it can work out where each row would have been if the whole frame had been captured at once. Each row is moved back by the measured movement multiplied by how much later the sensor read that row. Rows near the start of the readout move very little, rows near the end move the most, and the leaning lines straighten up.

The readout setting

Two settings control the correction. Readout is how long the sensor takes to read the frame, given as a share of the frame time. It defaults to 60 percent, which suits many phones. If your correction looks too weak, with lines still leaning, try a higher value. If it overcorrects, with lines leaning the other way, try a lower one.

Direction sets which way the sensor reads, top to bottom or bottom to top. Most cameras read top to bottom, but some read the other way, and footage that was flipped or rotated may also need the other direction. If the correction makes things worse, try switching it.

Where it fits with stabilising

Rolling shutter and shake often come together, but they are different problems. Stabilising moves the whole frame to cancel out shake. Rolling shutter repair corrects the shape inside the frame. A stabiliser on its own can even make rolling shutter more obvious, because once the frame is steady, the wobble inside it stands out.

For footage with both, apply rolling shutter repair and then stabilise. Video by Zaweba offers Clip, then Stabilise for a quick steadied copy, and the stabiliser effect with smoothness, zoom, edge handling and a perspective mode for more control.

Getting the best from it

Test on the worst moment. Find the fastest pan or the most jelly-like vibration in the clip, set the readout there, then play the whole clip to make sure it holds up.

Look at straight lines. Door frames, poles and building edges show clearly whether the correction is right. When they stand upright during movement, you are close.

Accept its limits. Very fast, irregular vibration, such as a camera bolted to an engine, may be beyond full repair, since the movement changes faster than it can be measured cleanly. The effect can reduce it, but prevention is better: use a higher frame rate, avoid very fast pans, and add some damping between the camera and the vibration.

Rolling shutter repair in Video by Zaweba is one of those tools you don't think about until you need it, and then it can save a shot you thought was ruined.