The clip above shows a small animal there, then gone, with the ground still tracking naturally under the camera instead of smearing into a patch. A person is the harder version of that same job in After Effects: bigger, usually walking through the frame instead of sitting still, and dragging a shadow along with them.
The After Effects route
Roto Brush is the fastest way to isolate a person without hand-drawing the outline frame by frame; one click or stroke gives you a rough mask you can refine. Once that mask exists, the Content-Aware Fill panel fills the space left behind using nearby frames. If the person is standing in front of a flat surface the mask also needs to track, like a wall or a floor, Mocha AE, which ships with After Effects, adds planar tracking for that.
Where it breaks
All three are built around a short, fairly stable range. A person walking changes shape every step, and if the camera is moving too, Content-Aware Fill has to invent more of the background from less reliable surrounding frames than a still object ever requires. That shows up as a smeared patch where the person used to be, a flicker where the fill loses track of what's behind them, or a faint outline where Roto Brush's mask ran a few pixels short. The shadow is the most common miss: if the mask only caught the body, the shadow stays on the ground after the person is gone, and that's usually the first thing a viewer notices.
The AI pass, for a person that moves
The fix is the same tracked-mask idea, scaled to a bigger, more complex subject than Roto Brush is built to hold steady on its own.
1. Mask the whole clip, not one frame
Draw or generate the mask on a frame where the person is clearest, then track it forward and backward through the shot. Scrub the result and fix the mask only where it drifts, usually where they turn, are partly blocked, or cross someone else.
2. Grow the mask to cover the shadow and reflection
A person removed cleanly but still casting a shadow on the ground, or still visible in a window or puddle, is the fix to make before anything else.
3. Remove and rebuild the background across the shot
Run the removal on the tracked region so the background behind the person is rebuilt over time instead of patched frame by frame. That's what keeps it moving naturally with the camera instead of sitting on top of the image.
4. Round-trip back to After Effects
Export the result as EDL, FCPXML or OpenTimelineIO and bring it into your After Effects project. The comp work, grade and final delivery stay exactly where you'd normally do them.
Asking an agent to do the AI pass
Remove the person walking through this shot. Track them through the whole clip, including their shadow, and keep the background moving naturally with the camera. Show me the result before replacing the original, then export it as an EDL.
With the run mode set to review, the agent masks and removes the person and waits for your approval before touching the original clip. You decide if it's clean, and the export is what lands back in your After Effects project.
When Roto Brush and Content-Aware Fill are enough
If the person barely moves, the camera is locked off, and the shot runs a couple of seconds, Roto Brush into Content-Aware Fill will get there faster than setting up a separate pass, and you never leave After Effects. Reach for the tracked-mask route once the person is walking, turning, or getting crossed by someone else, or the shot is long enough that fixing the fill by hand, frame after frame, would take longer than the removal itself.
Download the free Shoty editor for the tracked-mask route. For the DaVinci Resolve version of this job, see remove person from video DaVinci Resolve, and for the masking step on its own, AI rotoscoping.