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Crop video

Crop to a ratio preset (1:1, 16:9, 9:16, 4:3, 3:4) or an exact rectangle. Everything runs in your browser; your file never leaves your device.

How Crop video works

Crop a video to a specific rectangle or aspect ratio inside your browser, with ffmpeg WebAssembly handling every pixel on your own device. Pick one of the centred ratio presets (1:1 square, 16:9 landscape, 9:16 vertical, 4:3, 3:4) to frame social-media formats in one click, or enter a custom width, height, and offset to cut an exact region. The ffmpeg crop filter (crop=W:H:X:Y) re-encodes the frame area you keep using libx264 while copying the audio track untouched.

Because the frame dimensions change, a full pixel re-encode of the video stream is unavoidable, unlike rotation which can use metadata tricks. Expect processing time proportional to the clip length and your CPU speed. The output is MP4 H.264, which plays on every modern device.

Written by Bastien Sulyan

How to use Crop video, step by step

  1. Drop or select the video you want to crop.
  2. Choose a ratio preset (1:1, 16:9, 9:16, 4:3, 3:4) for a centred crop, or switch to manual mode to enter exact pixel dimensions and position.
  3. Preview the crop region if the tool offers a preview frame.
  4. Click Crop and let ffmpeg apply the crop=W:H:X:Y filter on your device.
  5. Download the cropped MP4 when processing finishes.

Common use cases

  • Converting a 16:9 YouTube recording into a 9:16 vertical clip for TikTok or Instagram Reels without a separate editing app.
  • Cutting out a 1:1 square from a landscape conference recording to share as a social post.
  • Removing unwanted letterbox bars or watermarks at the edges of a video by cropping to a manual pixel rectangle.
  • Extracting a specific area of a screen-recording tutorial to zoom in on the relevant UI element.

Frequently asked questions

Does cropping re-encode the whole video, or just cut around the edges?

Cropping always requires a full pixel re-encode of the video stream because the frame dimensions change. ffmpeg applies the crop filter with libx264 at high quality, so any quality reduction is minor. The audio track is copied without re-encoding, which keeps it lossless.

Is my video processed on a server when I crop it?

No. The ffmpeg crop filter runs inside your browser tab via WebAssembly. Your file stays in your device's local memory from start to finish, and the cropped MP4 is downloaded directly to your device. There is no upload step.

How do I crop to a 9:16 aspect ratio for TikTok?

Select the 9:16 preset from the ratio list. The tool calculates the largest centred 9:16 rectangle that fits within your source frame, then crops to that rectangle. If you need the crop to focus on a specific part of the frame rather than the centre, use manual mode to set the top-left offset.

Can I crop a WebM or MOV file?

Yes. ffmpeg.wasm reads most common formats as input. The output is always MP4 with H.264 video and copied audio, regardless of the source format.

What happens to the audio during the crop?

The audio stream is copied exactly as-is with -c:a copy, so it is not re-encoded and there is no quality change. The duration is trimmed to match the video if necessary.

Why is cropping slower than muting or rotating?

Muting removes a stream entirely and rotation can often rewrite only the container metadata, both of which avoid re-encoding video frames. Cropping must decode every frame, cut the pixel area, and re-encode it with libx264, which is CPU-intensive and scales with clip length and resolution.

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