Choose a shape and the video is redrawn into it, frame by frame, then encoded again. The live preview shows a real frame from your file in the new shape before anything is encoded, because the only way to know whether a crop works is to look at it. Nothing is uploaded — the work happens on your own device.
The size you pick is the short edge, because that is what people mean by a resolution: vertical 1080p is 1080 wide and 1920 tall. How the picture fills the new shape is the important choice, and there are three ways to do it. Blurred fill scales the whole frame to fit and puts an enlarged, blurred copy of the same frame behind it, so nothing is cropped and nothing is black. Fill and crop fills the frame completely and cuts away whatever does not fit. Fit with bars shows the whole picture on a flat colour.
Choosing how to fit
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Blurred fill is the default for good reason:
it loses nothing from the picture and does not leave black bars, which is why it is what Instagram and the popular editing apps do. On a busy scene it looks deliberate rather than like a compromise.
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Fill and crop is cleaner and costs you the edges:
going from widescreen to vertical throws away most of the width, so a subject standing to one side disappears. The estimate says how much is being cut, and the crop position can be moved off centre.
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Fit with bars keeps everything and looks dated:
it is the right answer when the whole frame genuinely matters — a screen recording, a diagram, anything where cropping loses information rather than scenery.
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Reshaping always re-encodes:
the picture is redrawn into a new frame, so there is a small quality cost. Work from the best source you have rather than from something already reshaped once.
The size you enter is the short edge
Entering 1080 for a 9:16 shape produces 1080 wide by 1920 tall, not the other way round, because the short edge is what people actually mean by a resolution figure — vertical 1080p is 1080 wide. The [msm_tool slug="video-cropper"] reads the number that way for every shape on offer, which is the fix for an earlier version that read it as the long edge and quietly produced narrower output than anyone asked for.
Blurred fill is the default, and why
The whole frame is scaled to fit within the new shape, and the empty space left around it is filled with an enlarged, blurred copy of that same frame. Nothing is cropped out and no black bars appear, which is why it has become the convention on Instagram and most editing apps rather than an unusual choice here. On busy footage it reads as deliberate rather than as a compromise the video is making.
Fill and crop is cleaner, and it costs the edges
Filling the frame completely and cutting away whatever does not fit gives a cleaner, edge-to-edge result, at the cost of whatever was standing near the sides. Turning a widescreen recording into a vertical one this way discards most of the original width, so a subject who was not centred can disappear from the frame entirely. The crop position can be moved off centre to compensate once the estimate shows how much is being lost.
Fit with bars keeps everything and looks dated
Nothing is cropped and nothing is scaled to fill — the whole picture sits inside the new shape with flat colour making up the difference. It looks like an older broadcast format, which is exactly why it is the right choice on the occasions when the whole frame genuinely carries information: a screen recording, a diagram, anything where cropping would remove content rather than background.
Reshaping always re-encodes
Every frame is redrawn into the new shape and the video is encoded again afterwards, which is a small but real quality cost regardless of which fitting mode is chosen. It is worth reshaping from the best copy of a recording available rather than from something that has already been through this once.
A bigger output does not mean a sharper one
Choosing a larger resolution than the source spreads the existing picture over more pixels rather than inventing new detail to fill them, so the result looks softer rather than sharper. Starting from the largest version of a recording available is the only way to actually gain resolution.