To extract only a small segment in the middle of a movie, it can be used in combination with -t which specifies the duration, like -ss 60 -t 10 to capture from second 60 to 70. Or you can use the -to option to specify an out point, like -ss 60 -to 70 to capture from second 60 to 70. -t and -to are mutually exclusive. If you use both, -t will be used.

Note that if you specify -ss before -i only, the timestamps will be reset to zero, so -t and -to have not the same effect. If you want to keep the original timestamps, add the -copytsoption.

The first command will cut from 00:01:00 to 00:03:00 (in the original), using the faster seek.
 The second command will cut from 00:01:00 to 00:02:00, as intended, using the slower seek.
 The third command will cut from 00:01:00 to 00:02:00, as intended, using the faster seek.