Extract Sub-Image from Video to BMP with FFmpeg

This article provides a quick and practical guide on how to extract a specific portion of a video frame (a sub-image) at a precise timestamp and save it as a BMP image using the powerful command-line tool FFmpeg. You will learn the exact command syntax and how to configure the cropping coordinates to get the perfect image extract.

To extract a cropped sub-image from a video and save it as a BMP, you need to combine FFmpeg’s seeking capability with its cropping video filter.

The FFmpeg Command

Run the following command in your terminal:

ffmpeg -ss 00:01:30 -i input.mp4 -vf "crop=w=400:h=300:x=100:y=150" -vframes 1 output.bmp

Parameter Breakdown

• -ss 00:01:30: Seeks to the exact timestamp in the video where you want to extract the frame (formatted as HH:MM:SS or in seconds, e.g., 90). Placing this before -i ensures fast seeking.
• -i input.mp4: Specifies the path to your source video file.
• -vf "crop=w=400:h=300:x=100:y=150": Applies the video crop filter.
  • w: The width of the sub-image you want to extract (e.g., 400 pixels).
  • h: The height of the sub-image you want to extract (e.g., 300 pixels).
  • x: The horizontal coordinate of the top-left corner of the crop area (e.g., 100 pixels from the left edge).
  • y: The vertical coordinate of the top-left corner of the crop area (e.g., 150 pixels from the top edge).
• -vframes 1: Instructs FFmpeg to stop processing after exporting exactly one frame.
• output.bmp: The name of the output file. FFmpeg automatically recognizes the .bmp extension and encodes the image in the uncompressed BMP format.