Stabilisation, and the crop it costs

What it does, mechanically

Stabilisation analyses the movement between frames, works out how much of that movement is unwanted shake, and then moves each frame in the opposite direction to cancel it.

Moving a frame leaves empty space at the edges. To avoid showing that space, the stabiliser scales the image up and crops. That crop is the price, and there is no version of this that does not pay it.

Typical cost: 5 to 15% of the frame for handheld walking footage, more for anything violent. This is another reason to shoot larger than you deliver — a 4K source at 1080p can lose 15% and still be at full delivery resolution.

The two kinds

Translation-only. The frame slides horizontally and vertically. Cheap, fast, and sufficient for a locked-off shot with small wobble.

Full transform. Position, rotation, scale and perspective, often with the frame warped non-uniformly to correct rolling-shutter skew. Better results and a larger crop.

Resolve offers three modes on the colour page, and they behave differently enough to be worth knowing:

• Perspective — the full model. Best on footage with a lot of parallax and depth.
• Similarity — translation, rotation and zoom, no perspective. More stable on footage where the perspective analysis gets confused.
• Translation — position only. Use when the others produce a wobbling, swimming result.

If one mode produces swimming, try the next one down. This is the single most useful troubleshooting step and most people never discover it.

Smooth against locked

A second decision: do you want the camera to hold still, or to move smoothly?

Camera Lock removes all movement, producing a shot that looks tripod-mounted. It works on short clips and fails on long ones, because any real drift in the camera eventually exhausts the available crop.

Smooth keeps the intended movement and removes only the high-frequency shake. This is what you want for a walking shot, a pan, or anything where the camera was meant to move. Resolve exposes a Smooth parameter; higher values remove more of the low-frequency motion and cost more crop.

Rolling shutter, and the wobble that is not shake

Most sensors are read out line by line rather than all at once. During a fast pan or a hard vibration, the top of the frame is captured a few milliseconds before the bottom, so vertical lines lean and the image appears to wobble like jelly.

Stabilisation alone makes this worse in some cases: cancelling the frame's overall movement leaves the internal skew, now moving against a stationary background, which is more visible than it was.

The fix is a rolling-shutter correction pass, applied before or alongside stabilisation. Resolve has one in the stabilisation controls; the free ffmpeg route is vidstab plus deshake, which does not model rolling shutter and will leave the skew.

Extreme cases — a propeller, a guitar string, a whip pan — cannot be corrected and stay bent.

When it will not work

Motion blur is baked in. Stabilisation repositions frames; it cannot remove the blur that a shaking camera put into each one. A stabilised shot from a very shaky source is a steady sequence of blurred frames, which looks strange — steady and soft at once.

Nothing trackable in frame. A featureless wall, heavy fog, a night shot that is mostly black. The analysis has no points to follow.

Large moving objects dominating the frame. A car passing close to camera can be tracked instead of the background, and the stabiliser will hold the car still and move the world.

Cuts inside the clip. Stabilise each shot separately. A single analysis across a cut produces nonsense.

Free tools

Resolve's stabiliser is on the colour page in the free version, with all three modes and rolling-shutter correction. It is good.

FFmpeg's vidstab is a two-pass filter and genuinely useful for batch work:

ffmpeg -i shaky.mp4 -vf vidstabdetect=shakiness=6:accuracy=15 -f null -
ffmpeg -i shaky.mp4 -vf vidstabtransform=smoothing=20:zoom=2,unsharp=5:5:0.8 \
       -c:a copy stable.mp4

Kdenlive exposes vidstab through its interface, which is the easiest free graphical route outside Resolve.

The editorial alternative

Before stabilising, ask whether the shake is a problem. A handheld shot that moves with a person reads as immediacy; the same shot stabilised into unnatural steadiness can read as uncanny. Documentary footage in particular is often better left alone.

And the cheapest fix is sometimes to use the shot for less time. Two seconds of shake reads as energy; twelve seconds reads as a fault.

Today

Stabilise a handheld clip in all three modes and compare. Then look at how much the frame was cropped in each. That number is what the technique costs you.