Turning a 16:9 video into a 9:16 one for TikTok, Instagram Reels or YouTube Shorts means throwing away two-thirds of every frame. The quick way is a center crop: keep the middle 606 of the 1,920 pixels and drop the sides. That works as long as the person stays in the middle. In the 7.5-second, three-shot clip used below, a center crop cuts the subject in half in the first shot and loses her completely in the third, where all that is left is her reflection in a shop window.
The fix is to move the crop, shot by shot, to wherever the subject is. Editors call this reframing. The steps below use the video editor in the osFoundry desktop app, whose "Reframe following the subject" preset does it on your computer without an AI model, so it costs nothing.
Add the clip to the video editor
Open the video editor and add the clip with the "Add a shot from a file" button above the Shots list. The file is read from your disk; nothing is uploaded. The clip here is a 1920×1080, 30 fps edit of three shots: a woman walking past a building on the left of the frame, a second person walking away in the middle, and the first woman again on the right.
Find the reframe preset
Select the clip on the timeline first, so the preset works on it. Then open Presets in the left bar and search for "reframe". The card that comes up, "Reframe following the subject", is marked Ready. Most of the presets around it say "Needs a model"; this one only runs ffmpeg on your machine and needs no model and no API key.
Pick the shape and apply
The preset opens with Vertical (9:16) selected, with Square and Landscape as the alternatives. "How fast the frame may move" is set to 0.05: the frame may travel at most 5% of the picture per step, so it doesn't jump across when someone else walks into view. Leave both as they are and click Apply.
Two things happen. The app shrinks the video to a 64×36 grey grid, four frames a second, and checks which squares changed from one frame to the next. Against a still background, what changed is the person. It also finds the cuts between shots. Each shot then gets one fixed 9:16 frame, placed around where the movement was on average, and a message confirms "Reframed to 9:16 across 3 shots".
Check each shot
In this clip the cuts were found at 1.77 and 4.73 seconds, and the three crops start 369, 668 and 932 pixels from the left edge. The center crop starts at 657 in every shot:
One crop per shot, rather than a frame that keeps moving, is deliberate. A crop that follows every movement turns into a pan nobody asked for, and if the tracking gets one shot wrong, the mistake stays in that shot. It can go wrong: on a busy street the thing that moves most may be the traffic. In that case drag the circle on the picture ("Lock the subject") onto the person and apply again, and the frame stays where you put it.
Doing it without the app
Any editor can do the same thing by hand: split the clip at each cut, set the sequence to 9:16, and slide each part sideways until the person is inside the frame. Premiere Pro's Auto Reframe and DaVinci Resolve Studio's Smart Reframe automate it in paid apps. Whichever way you do it, watch every shot before posting, because a vertical frame leaves almost no room at the edges.
The editor is described on the page for osFoundry's video editor, and the app is free from the osFoundry download page for macOS, Windows and Linux.
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