90.9 Video Image Crop
This section deals with cropping the video image over the extent of the video. If you are wanting to extract time extents of the video (i.e., trim or cut the video) see Section 90.17.
Using ffmpeg we can remove, for example, the right most 230 pixel wide margin of a video with the following command.
$ ffmpeg -i input.mp4 -vf "crop=iw-230:ih:0:0" cropped.mp4
The input video is identified using
-i. Video filtering is
-vf as a shorthand for
-filter:v. A filtergraph
is provided as the argument to the video filtering. The final
parameter names to output video file.
A crop filter is utilised through the filtergraph. The filter’s first parameter is the width of the output video. Here, iw refers to the original input video’s width from which we subtract the amount that we wish to crop. The second parameter is the height of the output video which using ih as the input video height retains the original height. The next two parameters are the x (horizontal) and y (vertical) positions of the input video that will become the left and top edge of the output video. Thus 0:0 indicates no cropping on the left or the top.
crop=iw-230:ih:0:0 will crop 230 pixels from the
right edge of the video, for every frame.
To determine what to crop, extract a single frame from the video:
$ ffmpeg -ss 0.5 -i input.mkv -vframes 1 frame.jpg
frame.jpg into gimp and measure the
pixels on the left and top, and the right and bottom, to crop. Then
modify the crop options. For example, to crop 40 pixels from the left,
and 64 from the top, with the resulting video being 772 pixels wide
and 431 high:
$ ffmpeg -i input.mkv -vf "crop=772:431:40:64" cropped.mkv
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