$ ffmpeg -i me.avi |& grep Dura
  Duration: 00:01:43.27, start: 0.000000, bitrate: 16330 kb/s

# e.g. from start to 1 min.
$ ./ffmpeg -i me.avi -vcodec copy -acodec copy -t 00:01:00 output1.avi
# e.g. from 1 min. to end
$ ./ffmpeg -i me.avi -vcodec copy -acodec copy -ss 00:01:00 output2.avi

$ ls -l me.avi output*
-rw-rw-r-- 1 saml saml 210816000 Nov 27 21:36 me.avi
-rw-rw-r-- 1 saml saml 120361978 Nov 27 21:39 output1.avi
-rw-rw-r-- 1 saml saml  90571034 Nov 27 21:40 output2.avi

$ ./ffmpeg -i output1.avi |& grep Dura
  Duration: 00:01:00.00, start: 0.000000, bitrate: 16048 kb/s
$ ./ffmpeg -i output2.avi |& grep Dura
  Duration: 00:00:43.27, start: 0.000000, bitrate: 16743 kb/s