How can I crop a video with ffmpeg?
Use the crop filter:
ffmpeg -i in.mp4 -filter:v &quot;crop=out_w:out_h:x:y&quot; out.mp4

Where the options are as follows:

out_w is the width of the output rectangle
out_h is the height of the output rectangle
x and y specify the top left corner of the output rectangle

Original image

Original 320x240 image
Example 1

To crop a 80×60 section, starting from position (200, 100):
ffmpeg -i in.mp4 -filter:v &quot;crop=80:60:200:100&quot; -c:a copy out.mp4


The audio is stream copied in this example, so re-encoding is avoided.

Example 2

To crop the bottom right quarter:
ffmpeg -i in.mp4 -filter:v &quot;crop=in_w/2:in_h/2:in_w/2:in_h/2&quot; -c:a copy out.mp4

This is the same as:
ffmpeg -i in.mp4 -filter:v &quot;crop=320/2:240/2:320/2:240/2&quot; -c:a copy out.mp4

Which is the same as:
ffmpeg -i in.mp4 -filter:v &quot;crop=160:120:160:120&quot; -c:a copy out.mp4


You can refer to the input image size with in_w and in_h as shown in this first example. The output width and height can also be used with out_w and out_h.

Example 3

Crop 20 pixels from the top, and 20 from the bottom:
 ffmpeg -i in.mp4 -filter:v &quot;crop=in_w:in_h-40&quot; -c:a copy out.mp4


The filter will automatically center the crop if x and y are omitted such as in this example.

Previewing
You can take a crop (heh heh) and preview it live with ffplay:
ffplay -i input -vf &quot;crop=in_w:in_h-40&quot;

This way you can experiment and adjust your cropping without the need to encode, view, repeat.
Notes

crop filter documentation

Default encoder for MP4 is libx264 (H.264 video) or mpeg4 (MPEG-4 Part 2 video) depending on your ffmpeg build. See FFmpeg Wiki: H.264 Video Encoding Guide for more info.

Instead of cropping and re-encoding, consider cropping upon playback. This is possible with any player worth using.

Ancient ffmpeg builds used -croptop, -cropbottom, -cropleft, -cropright options instead of the crop filter. If this is the case for you then get a modern ffmpeg. Development is very active and there is no reason to use an antique.