FFMPEG COMMAND

Resize a video with FFmpeg

The scale filter does the work. The examples below downscale 1080p to 720p, halve a video, fit it into a square with padding and fill a 9:16 frame by cropping, each checked with ffprobe.

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

the command

ffmpeg -i input.mp4 -vf "scale=1280:-2" -c:v libx264 -crf 23 -preset medium -c:a copy output.mp4

Scales the width to 1280 px and lets FFmpeg compute an even height that keeps the aspect ratio: the 1920x1080 test file became 1280x720. The video is re-encoded at CRF 23, the audio is copied. Size went from 9.9 MB to 2.5 MB.

Flags, explained

-vf "scale=1280:-2": Video filter: scale to width 1280, height computed to keep the aspect ratio and rounded to an even number.
-2: Auto-compute this dimension, keeping it divisible by 2. -1 also auto-computes but can yield an odd size, which the H.264 encoder rejects with yuv420p.
force_original_aspect_ratio=decrease: Shrink until the whole picture fits inside the target box. Use increase to cover the box (then crop).
pad=W:H:x:y: Add borders to reach W x H, placing the picture at x,y. (ow-iw)/2 centres it horizontally.
crop=W:H: Keep a W x H window from the centre of the frame.
-crf 23 -preset medium: x264 defaults: good quality at a reasonable size. Lower CRF means bigger and better.
-c:a copy: Audio is untouched by scaling, so copy it instead of re-encoding.

Variants

Set the height instead of the width

shell

ffmpeg -i input.mp4 -vf "scale=-2:720" -c:v libx264 -crf 23 -preset medium -c:a copy output.mp4

Same result on a 16:9 source (1280x720). Use this form when the target height is what you know.

Halve the dimensions

shell

ffmpeg -i input.mp4 -vf "scale=iw/2:-2" -c:v libx264 -crf 23 -preset medium -c:a copy output.mp4

iw and ih are the input width and height, so the expression works on any source. 1920x1080 became 960x540.

Fit inside a square with padding (no cropping)

shell

ffmpeg -i input.mp4 -vf "scale=1080:1080:force_original_aspect_ratio=decrease,pad=1080:1080:(ow-iw)/2:(oh-ih)/2" -c:v libx264 -crf 23 -preset medium -c:a copy square.mp4

force_original_aspect_ratio=decrease scales the video so it fits inside 1080x1080, then pad fills the rest with black and centres the picture. Output: 1080x1080 with the 16:9 picture letterboxed.

Fill a 9:16 frame by cropping the sides

shell

ffmpeg -i input.mp4 -vf "scale=1080:1920:force_original_aspect_ratio=increase,crop=1080:1920" -c:v libx264 -crf 23 -preset medium -c:a copy vertical.mp4

increase scales the video until it covers 1080x1920, then crop cuts the centre. The subject must be in the middle of the frame or it gets cut off. Output: 1080x1920.

Sharper downscale with Lanczos

shell

ffmpeg -i input.mp4 -vf "scale=1280:-2:flags=lanczos" -c:v libx264 -crf 23 -preset medium -c:a copy output.mp4

Same 1280x720 output with the Lanczos resampler instead of the default bicubic. Slightly sharper edges, slightly larger file (2.8 MB against 2.5 MB here).

Pitfalls we hit

scale=640:-1 fails on sources whose aspect ratio gives an odd height. A 1280x714 test clip produced "height not divisible by 2" and no output; scale=640:-2 always works.
-s 1280x720 forces the exact size and distorts anything that is not 16:9. The scale filter with -2 keeps the aspect ratio.
Upscaling does not add detail; it only makes the file bigger. Encode at the source size and let the player scale.
Cropping to 9:16 with crop=1080:1920 keeps the centre of the frame. For interviews and talking heads that is usually right; for wide shots consider padding or a blurred background instead.

How we verified it

Run with FFmpeg 9.0.1 on 26 August 2026 against a 12 s, 1920x1080, 30 fps H.264/AAC file of 9,862,251 bytes. scale=1280:-2 → 1280x720, 2,532,339 bytes; scale=-2:720 → 1280x720; scale=iw/2:-2 → 960x540; square pad → 1080x1080; 9:16 crop → 1080x1920; lanczos → 1280x720, 2,784,789 bytes. scale=640:-1 on a 1280x714 clip failed with an odd height (640x357).

The same edit as a typed operation

resize_video takes a target aspect ratio or size plus a fit mode (cover crops, contain pads) and builds the scale, crop and pad chain itself, with even dimensions guaranteed. Odd sizes and distortion cannot happen.

MCP tool: resize_videoPOST /api/v1/tools/resize-video

request body

{
  "inputs": [{ "id": "main", "url": "https://example.com/video.mp4" }],
  "options": { "aspect_ratio": "9:16", "fit": "cover" }
}

Run resize video in the browser Connect MCP API docs

FAQ

How do I resize a video without losing quality?

Scaling always re-encodes the video, so choose a low CRF (18 to 20) and a slower preset to keep the loss invisible. The audio can be copied as is.

How do I resize to 1080p, 720p or 480p?

Use scale=-2:1080, scale=-2:720 or scale=-2:480. The width follows the aspect ratio and stays even.

What is the difference between scale, pad and crop?

scale changes the picture size. pad adds borders around it to reach a frame size without distortion. crop removes the outside of the picture to fill a frame. The fit variants above combine them.

Can I change the aspect ratio without cropping or black bars?

Only by distorting the picture, which is rarely wanted. The usual alternatives are padding, cropping, or a blurred copy of the video as background, which is what KinoPipe does for 9:16 by default.

Related commands

All FFmpeg commands