Hiding a jump cut with the smooth jump cut in Video by Zaweba

A jump cut happens when you take a piece out of the middle of a single shot. The camera hasn't moved, but the person in frame has, so at the join their head twitches a few pixels to one side and the viewer feels the edit. Video by Zaweba has a transition built for exactly this moment, called the smooth jump cut.

It sits with the other transitions, but it works differently from a dissolve. Instead of fading one picture through the other, it blends the two takes of the same shot using an optical-flow morph. The app looks at how the pixels move between the last frame before the cut and the first frame after it, and draws the frames in between so the face and shoulders slide into their new place rather than snapping there.

When it earns its place

The smooth jump cut is at its best on talking-head recordings: a piece to camera, an interview with a locked-off camera, a lecture filmed from a tripod. You record one long take, cut out the stumbles, the coughs and the long pauses, and you're left with a row of joins where nothing should have changed except the words. Those are the joins this transition was made for.

It also helps when you shorten a product demonstration or a screen-and-face recording where the background stays still. Anywhere the framing is identical on both sides of the cut and only the subject has shifted slightly, the morph has a good chance of hiding the join.

It is the wrong tool when the two sides of the cut are different shots. If the camera angle changes, or you're cutting from a wide to a close-up, there's nothing sensible to morph between, and a plain cut or a dissolve will look better. Big movements are also hard: if someone stood up or turned right round between the two takes, the in-between frames can look strange.

Putting one on a join

Make your edit first. Trim out the part you don't want so the two remaining pieces of the shot sit next to each other on the same track. Then add the smooth jump cut to that edit point the same way you'd add any other transition, from the transitions on offer in the app. Play it back and watch the face closely, because that's where people look.

Keep the transition short. The idea is that nobody notices it, so a long morph defeats the purpose and starts to look like a special effect. If a join still looks wrong, try nudging the cut a few frames either way. Picking the moment when the speaker's head is closest to where it is on the other side of the cut gives the morph less work to do, and the result is cleaner.

It helps to cut on a still moment. If the speaker is mid-gesture with a hand flying across the frame, the in-between frames have more to invent. A pause at the end of a sentence, when the head is level and the hands are down, is usually the easiest place to join.

Other ways to treat a jump cut

Not every jump cut needs hiding. Plenty of online videos leave them in on purpose because they keep the pace up, and an audience used to that style won't mind. If you'd rather show the cut honestly, a straight cut is fine.

When you want to hide it but the morph isn't convincing, you have the usual editor's tricks. Cover the join with a cutaway from another track, such as a screen recording, a photograph or a shot of what the speaker is talking about. Or punch in: scale the second half up slightly with the position and scale controls so the cut reads as a change of framing rather than a glitch.

The sound matters too. Even a perfect picture join can be given away by a click or a jump in room tone, so listen to the edit as well as watching it, and use a short sound crossfade if the background noise changes.

A tidy finish

Used on the right joins, the smooth jump cut in Video by Zaweba saves you from reshooting a take just because of one fluffed line. Cut out the mistake, lay the morph on the join, and check it at full speed before you move on.