The syntax for FFmpeg video cropping is like:

ffmpeg -i input.avi -vf crop=439:455:73:15 -c:v mjpeg -qscale 1 output.avi

-qscale 1

makes low compression (best possible MJPEG quality). qscale can go from 1 to 31.

The assumptions made above were that you wanted Motion JPEG video output of:

Obviously, change these pixel parameters to suit your particular video.