Crop Video in FFmpeg with Custom Dimensions

This guide explains how to use the FFmpeg crop video filter to trim the width and height of a video to your exact specifications. You will learn the basic command syntax, how the coordinate system works, and see practical examples for cropping videos from specific positions or centering the crop area.

To crop a video in FFmpeg, you use the video filter flag (-vf) followed by the crop filter. The basic syntax is:

ffmpeg -i input.mp4 -vf "crop=w:h:x:y" output.mp4

Understanding the Parameters

The crop filter accepts four primary arguments separated by colons:

• w (width): The width of the output (cropped) video.
• h (height): The height of the output (cropped) video.
• x (X-coordinate): The horizontal position of the left edge of the crop area, relative to the top-left corner of the input video. The default is the center of the input frame.
• y (Y-coordinate): The vertical position of the top edge of the crop area, relative to the top-left corner of the input video. The default is the center of the input frame.

Practical Examples

1. Crop to Specific Dimensions from a Custom Position

To crop a video to a width of 800 pixels and a height of 600 pixels, starting 100 pixels from the left edge (x=100) and 150 pixels from the top edge (y=150):

ffmpeg -i input.mp4 -vf "crop=800:600:100:150" -c:a copy output.mp4

(Note: -c:a copy is added to copy the audio stream without re-encoding, which saves processing time.)

2. Crop to the Center of the Video

If you want to crop a video to a specific size (e.g., 640x480) but want it perfectly centered, you can omit the x and y parameters. FFmpeg automatically centers the crop area by default:

ffmpeg -i input.mp4 -vf "crop=640:480" -c:a copy output.mp4

Alternatively, you can write this out explicitly using FFmpeg’s built-in variables in_w (input width) and in_h (input height):

ffmpeg -i input.mp4 -vf "crop=640:480:(in_w-640)/2:(in_h-480)/2" -c:a copy output.mp4

3. Crop a Video in Half (Left Side Only)

To keep only the left half of a video, you can use the input dimension variables directly in your values:

ffmpeg -i input.mp4 -vf "crop=in_w/2:in_h:0:0" -c:a copy output.mp4

This sets the output width to half of the input width (in_w/2), keeps the full height (in_h), and starts the crop from the top-left corner (0:0).