How to Swap Several Faces in One Clip Without Losing Track

You have a clip of two friends. You want a different face on each of them. The tool shows one toggle called Swap All Faces and no way to say who is who. Turn it on and everybody becomes the same person.

One source face per job, and what that forces

Start with the rule that shapes everything else. A job accepts a single source portrait. Every face the tool replaces in that run gets that one identity.

So Swap All Faces does not mean different faces for different people. It means the same face on all of them. That is great for a joke where five people share your head. It is useless when you want your face on the left person and your friend's face on the right.

Two identities means two jobs. Three means three. There is no version of this where one upload solves it.

How the tool ranks faces, and why it forgets between frames

The tool never knows anybody's name. It runs a face detector, gets a list of boxes, and sorts that list by size. Position 0 is the largest face in the picture. Position 1 is the next largest, and so on.

Size means pixels on screen, not age or importance. Whoever stands closest to the camera usually wins position 0. Lean forward during a clip and you can take that slot from someone else.

Here is the part that surprises people. On a GIF or a video, the detector runs again on every single frame. It does not carry a list forward. Frame 41 has no idea what frame 40 decided. So the ranking is rebuilt 24 or 30 times a second, from scratch.

Face Index exists on photos only

On the photo face swap you get a Face Index box under the Swap All Faces toggle. Switch the toggle off and the box appears, accepting 0 through 5. That is how you target the third person in a group shot instead of the nearest one.

The GIF and video tools do not have that box. You get the toggle and nothing else. Leave it on and every face is replaced. Switch it off and the tool takes the top ranked face in each frame, whoever that happens to be at the time.

Why the swap lands on the wrong person

Now the earlier facts add up to the classic failure. You turn Swap All Faces off because you only want one person changed. The tool then swaps the biggest face in each frame, independently.

For the first four seconds your friend is nearest the lens, so she gets the new face. Then she steps back and the other person leans in. The size order flips. From that frame on, the swap moves to the second person and stays there. Nothing errored. The tool did exactly what it was told.

Watch for this at three moments: someone walking toward the camera, someone leaning into frame to talk, and any cut to a different shot size. All three change who is largest.

The moment someone turns away

Profiles and back of head shots are not detected as faces. That person drops out of the list entirely for those frames, and the rest shift up a slot. When she turns back, she is added again, at whatever position her size earns.

With Swap All Faces on, this looks fine. Everyone gets the same identity, so a missing frame just leaves the original face for a moment. With the toggle off, it looks broken, because the swap hops to a new person and then hops back.

Do the faces one at a time

The reliable method is boring and it works. You isolate each person, swap them alone, and rebuild the shot at the end.

1. Upload the clip with source photo A. Turn Swap All Faces on. Every face becomes A. Save it as take A.
2. Upload the same clip again with source photo B. Save that as take B.
3. Open both takes in a free editor, one on top of the other, lined up at frame one.
4. Mask the top layer so it shows only the region around the person who should be B.
5. Move the mask a few times to follow that person, then export.

CapCut, DaVinci Resolve and iMovie all do this masking step, and the first two are free. Because both takes came from the same clip, the frames line up exactly. No stretching or resyncing is needed.

A worked example: two friends, twelve seconds

Say two people sit at a table, one on the left, one on the right, and neither moves much. Run take A and take B on the video face swap tool, roughly two minutes each. Stack them, then mask the top take down to the right half of the frame. Since nobody crosses the middle, one straight edge mask holds for the whole twelve seconds.

Now change one thing. Have them swap seats at second six. That single move turns a one mask job into a job with a mask that must animate. Plan the shot and you save yourself the fiddly part.

1 face~2 min

2 faces~14 min

3 faces~26 min

Example figures, to show the shape of the trade off. Render time uses the roughly two minute typical video job listed on the tool page. The rest is a rough allowance for masking each extra person in your own editor. Your numbers will differ.

What each extra face costs you

Faces in frame	What gets harder	What to do about it
1	Almost nothing. Ranking cannot change hands.	Leave Swap All Faces on and submit.
2	Size order flips when either person moves nearer.	Run two takes, then mask one side in an editor.
3 to 4	People overlap, so a face can vanish for a stretch of frames.	Pick a wide shot where all four are separated, then mask per person.
5 or more	Back rows get small, so detection misses them at random.	Accept one shared identity for everyone, or crop to a subgroup.
Crowd behind	Strangers in the background get swapped too.	Reframe to cut them out, or blur them before uploading.

That last row catches people out at parties and concerts. The tool cannot tell your group from the people behind you. Everyone in focus is a candidate.

Crowded frames are a different problem

A face needs roughly 40 pixels of width before the detector will place the eyes and mouth. In a wide group shot at 1080p, the back row often falls under that. Those faces flicker in and out of the list across the clip.

Resolution will not save you either. Uploading 4K does not help, because faces are analysed at a fixed internal size. It only makes the file heavier and eats into the upload cap. That cap is 5 MB on a free account and 100 MB on Pro.

The fix is framing, not settings. Get closer, or crop to the two or three people who matter. A tight shot of four faces beats a wide shot of twelve every time.

Shoot it so the tool can follow

When you control the recording, a few choices remove most of the trouble later.

Keep people apart on screen. Leave a gap between heads. Overlap is what makes masking painful and what makes faces disappear from the list.

Hold the camera still. A static shot means a static mask. Every pan or zoom is extra keyframes for you.

Keep depth consistent. Ask people to stay roughly the same distance from the lens. That stops the size ranking from flipping.

Match your source photos. Use portraits with similar light and a similar head angle, shot front on. Two sources that clash in lighting will read as two different edits in one frame.

Keep it short. Six seconds is plenty for a reaction. Fewer frames means fewer moments where something can go wrong. For a short loop, the GIF face swap tool is the faster route. Its frame cap is 150 on a free account and 300 on Pro.

Review the result at the crossing points

Do not watch the whole clip once and call it done. Jump straight to the moments you noted. Play each one at quarter speed if your player allows it.

Look for three things. The face jumping to a different person between two frames. A face snapping back to the original for a beat. Edges that flicker when heads pass each other. Those three cover nearly every multi face fault. If you see the swap hop between people, the cause is almost always Swap All Faces being off in a moving shot.

Do this next on your group clip

Want everyone to share one face? Turn Swap All Faces on and run a single job. Want different faces on different people? Run one job per identity on the same clip, then mask them together.

Test the idea on a still frame first. Export one frame from the clip. Run it through the photo tool with Face Index set. See whether the detector picks the person you want. That check takes about 30 seconds and saves a wasted video job. The pricing page lists daily job limits and frame caps per plan. Upload rules sit in the FAQ.