Source 1

Source 2

ffmpeg -i big_buck_bunny_720_stereo.mp4 -filter_complex "[0:v]crop=320:360:0:0[out1];[0:v]crop=320:360:320:0[out2]" -map [out1] -map 0:a out1.mp4 -map [out2] -map 0:a out2.mp4