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FFMPEG COMMAND

Crop a video with FFmpeg

The crop filter keeps a window of the frame and throws the rest away. Below: an explicit window, a centered square, a percentage-based crop, a 9:16 window and cropdetect for letterboxed sources, each checked with ffprobe.

Verified with FFmpeg 9.0.1 on 26 August 2026. Search intent: ffmpeg crop video.

the command
ffmpeg -i input.mp4 -vf "crop=640:360:320:180" -c:v libx264 -crf 23 -preset medium -c:a copy cropped.mp4

Keeps a 640x360 window whose top-left corner sits at x=320, y=180, which is the exact centre of a 1280x720 frame. The video is re-encoded (cropping changes pixels, so stream copy is impossible), the audio is copied. Output: 640x360, 360 frames, 1.6 MB from a 4.9 MB source.

Flags, explained

crop=w:h:x:y
Output width and height, then the top-left corner of the window in the source. x and y default to the centre when omitted.
iw, ih
Input width and height, usable in any of the four expressions (also in_w and in_h).
cropdetect=limit=24:round=2
Treat pixels darker than 24 as black and round the suggestion to a multiple of 2 so the result stays encodable.
-f null -
Decode and filter but write nothing, which is all cropdetect needs.
-c:v libx264 -crf 23 -preset medium
Re-encode the cropped frames at x264 defaults. Cropping always re-encodes.
-c:a copy
Audio is untouched by a crop, so copy it.

Variants

Centered square (1:1) without giving x and y

shell
ffmpeg -i input.mp4 -vf "crop=720:720" -c:v libx264 -crf 23 -preset medium -c:a copy square.mp4

When x and y are omitted the window is centered. On a 1280x720 source the full height is kept and 280 px are removed on each side. Output: 720x720, 3.1 MB.

Crop by percentage with iw and ih

shell
ffmpeg -i input.mp4 -vf "crop=iw:ih*0.8:0:ih*0.1" -c:v libx264 -crf 23 -preset medium -c:a copy banner.mp4

Keeps the full width and the middle 80 % of the height, removing 10 % top and bottom. Expressions make the command reusable on any source size. Output: 1280x576.

Vertical 9:16 window from the centre

shell
ffmpeg -i input.mp4 -vf "crop=406:720" -c:v libx264 -crf 23 -preset medium -c:a copy vertical.mp4

720 x 9/16 is 405, an odd number the encoder cannot take with yuv420p, so ask for 406. Output: 406x720. For a proper 1080x1920 deliverable scale first, see the vertical page.

Find black bars with cropdetect

shell
ffmpeg -i letterboxed.mp4 -t 2 -vf "cropdetect=limit=24:round=2" -f null -

Analyses two seconds and prints the crop it recommends on every frame. On a 1280x900 test file with 90 px black bars it printed crop=1280:720:0:90 for 59 frames in a row. Paste that value into the crop filter and encode.

Pitfalls we hit

  • Odd sizes are corrected silently: crop=405:720 produced a 404x720 file with no warning at -v error. Ask for even numbers when the output is yuv420p H.264.
  • A window larger than the frame or an x/y that pushes it outside is an error, not a clamp. Read the source size with ffprobe first (or use iw and ih expressions).
  • crop then scale and scale then crop give different pictures. To fill 1080x1920 from a 16:9 source, scale up first and crop second, or you crop a tiny window and upscale it.
  • cropdetect only sees the frames you feed it. A fade-in at the start reads as "all black"; skip a few seconds with -ss or sample the middle of the file.

How we verified it

Run with FFmpeg 9.0.1 on 26 August 2026 against a 12 s, 1280x720, 30 fps H.264/AAC file (4,896,094 bytes). Primary command: 640x360, 360 frames, 12.000 s, 1,588,227 bytes. crop=720:720: 720x720, 3,058,512 bytes. crop=iw:ih*0.8:0:ih*0.1: 1280x576, 4,129,942 bytes. crop=405:720 silently gave 404x720; crop=406:720 gave 406x720, 1,288,232 bytes. cropdetect on a 1280x900 letterboxed clip reported crop=1280:720:0:90 on 59 frames.

The same edit as a typed operation

crop_video takes a target ratio (9:16, 1:1, 4:5, 16:9) and a focus point, probes the source and computes an even-sized window that never exceeds the frame. The pixel maths and the encoder settings are decided for you, and the result comes back as a signed URL.

MCP tool: crop_videoPOST /api/v1/tools/crop-video
request body
{
  "inputs": [{ "id": "main", "url": "https://example.com/video.mp4" }],
  "options": { "aspect_ratio": "4:5", "focus": "top" }
}
Run crop video in the browser Connect MCPAPI docs

FAQ

The kept pixels are re-encoded once, so a small generation loss applies, kept negligible at -crf 18 to 23. There is no way to crop with stream copy because the compressed frames describe the whole picture.

Use crop=H:H where H is the source height, for example crop=720:720 on a 1280x720 file. Without x and y the window is centered. Add scale=1080:1080 afterwards if a platform wants a fixed size.

Run cropdetect on a few seconds of the file with -f null -, read the crop=... value it prints, then run a second command with that value in the crop filter. FFmpeg does not apply the detection by itself.

The window must fit inside the frame: w + x cannot exceed the source width and h + y cannot exceed the height. Check the source dimensions with ffprobe and use iw and ih expressions to stay inside.

Related commands

All FFmpeg commands