Crop a video online
Crop video by dragging a box over the picture, with 9:16, 1:1 and 4:5 presets and one-click black-bar removal. No watermark and no length limit.
- Runs in your browser
- Files are never uploaded
- Free, no account
First use downloads the 10 MB video engine from this site. After that it is cached and works offline. It is WebAssembly served from onthisdevice.com — no third-party CDN — and your file is still processed entirely on your own device.
Cropping is not the same as resizing
Cropping throws away the parts of the frame outside your rectangle: the subject stays exactly the size it was, and the picture gets smaller. Resizing keeps the whole frame and scales it, so nothing is lost but everything gets smaller. Use cropping to change the shape of a video or to cut something out of the edge of the frame; use resize video when the file needs to be a lower resolution.
Social presets, and the dimensions behind them
| Preset | Where it is used | Typical export size |
|---|---|---|
| 9:16 | TikTok, Instagram Reels, YouTube Shorts, Stories | 1080×1920 |
| 1:1 | Instagram feed square, LinkedIn, older Facebook posts | 1080×1080 |
| 4:5 | Instagram portrait — the largest shape the feed allows | 1080×1350 |
| 16:9 | YouTube, Vimeo, presentations, most screens | 1920×1080 |
| 4:3 | iPad, older displays, some documentation tools | 1440×1080 |
A preset locks the rectangle’s shape and fits the largest version of it inside your frame, so you only have to drag it to where the subject is. The exported file has the real dimensions of the crop — it is a genuine vertical video, not a horizontal one with black bars added.
Removing black bars
Letterboxing gets baked into a file whenever a widescreen clip is exported into a 4:3 frame, or a vertical phone video is placed in a horizontal timeline. The bars are real pixels; the only way to be rid of them is to crop them off.
The Remove black bars button runs FFmpeg’s cropdetect filter over the
opening seconds of the clip. It measures how far the near-black area extends from each edge
and proposes a rectangle. Treat it as a suggestion: a clip that fades in from black, or one
with a dark first shot, can fool it. Check the edges in the preview before exporting.
Cropping without a mouse
The whole tool works from the keyboard. The four number fields set the crop in exact source pixels, which is also the precise way to do it. The rectangle itself is focusable: Tab to it, then arrow keys move it one pixel, Shift with an arrow moves it ten, and Alt with an arrow resizes it. The rectangle’s accessible name always reports the current position and size, so a screen reader user gets the same information the visual overlay gives.
Why the numbers are always even
H.264 stores colour information at half the resolution of brightness — 4:2:0 chroma subsampling — so a frame with an odd width or height is not encodable. Rather than fail with an FFmpeg error most people cannot read, the tool rounds the crop down by a pixel and shows you the number it will actually use.
What the export costs
Cropping changes the picture, so the video is re-encoded — there is no lossless path, unlike trimming or re-wrapping. The default CRF 23 is visually clean for sharing; choose the high quality preset if the clip will be edited further, because each additional re-encode compounds the loss. The soundtrack is re-encoded to AAC 192 kbps so that the result is a clean MP4 whatever the source container was.
No watermark is added, there is no length limit and there is no upload. Compare that with the big online editors, which watermark free exports, cap clips at a few minutes and push the whole file through their servers first.
Questions
Does cropping re-encode the video?
Yes, it has to. Cropping changes the picture itself, so every frame is decoded, trimmed and re-compressed as H.264. The quality setting controls how much detail survives; at the default CRF 23 the loss is not visible in normal viewing.
How do I crop for TikTok, Reels or Shorts?
Choose the 9:16 preset. The rectangle locks to that shape, fills as much of the frame as it can and centres itself, and you can then drag it to frame the subject. The exported MP4 is a true vertical video, not a letterboxed one.
What does “remove black bars” actually do?
It runs FFmpeg’s cropdetect filter over the first few seconds of your clip, which measures where the picture stops being black, and sets the rectangle to what it finds. It is a suggestion, not gospel — check the edges before exporting, especially on a clip that opens with a fade from black.
Can I crop without using a mouse?
Yes. The four number fields set the crop in exact source pixels, and the rectangle itself is focusable: arrow keys move it a pixel at a time, Shift plus arrow moves it ten, and Alt plus arrow resizes it.
Why are the width and height rounded to even numbers?
H.264 stores colour at half resolution (4:2:0 chroma subsampling), so an odd width or height is simply not encodable. The tool rounds down by one pixel rather than failing with a cryptic FFmpeg error.